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 [matplotlib-devel] Problem with Agg Ellipses From: James Evans - 2007-12-08 00:03:12 Attachments: Message as HTML ```=0A= # This example can be boiled down to a more simplistic example=0A= # to show the problem, but bu including the upper and lower=0A= # bound ellipses, it demonstrates how significant this error=0A= # is to our plots.=0A= =0A= import math=0A= from pylab import *=0A= from matplotlib.patches import Ellipse=0A= =0A= # given a point x, y=0A= x =3D 2692.440=0A= y =3D 6720.850=0A= =0A= # get is the radius of a circle through this point=0A= r =3D math.sqrt( x*x+y*y )=0A= =0A= # show some comparative circles=0A= delta =3D 6=0A= =0A= =0A= ##################################################=0A= def custom_ellipse( ax, x, y, major, minor, theta, numpoints =3D 750, = **kwargs ):=0A= xs =3D []=0A= ys =3D []=0A= incr =3D 2.0*math.pi / numpoints=0A= incrTheta =3D 0.0=0A= while incrTheta <=3D (2.0*math.pi):=0A= a =3D major * math.cos( incrTheta )=0A= b =3D minor * math.sin( incrTheta )=0A= l =3D math.sqrt( ( a**2 ) + ( b**2 ) )=0A= phi =3D math.atan2( b, a )=0A= incrTheta +=3D incr=0A= =0A= xs.append( x + ( l * math.cos( theta + phi ) ) )=0A= ys.append( y + ( l * math.sin( theta + phi ) ) )=0A= # end while=0A= =0A= incrTheta =3D 2.0*math.pi=0A= a =3D major * math.cos( incrTheta )=0A= b =3D minor * math.sin( incrTheta )=0A= l =3D sqrt( ( a**2 ) + ( b**2 ) )=0A= phi =3D math.atan2( b, a )=0A= xs.append( x + ( l * math.cos( theta + phi ) ) )=0A= ys.append( y + ( l * math.sin( theta + phi ) ) )=0A= =0A= ellipseLine =3D ax.plot( xs, ys, **kwargs )=0A= =0A= =0A= ##################################################=0A= # make the axes=0A= ax =3D subplot( 211, aspect=3D'equal' )=0A= ax.set_aspect( 'equal', 'datalim' )=0A= =0A= # make the lower-bound ellipse=0A= diam =3D (r - delta) * 2.0=0A= lower_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, = edgecolor=3D"darkgreen" )=0A= ax.add_patch( lower_ellipse )=0A= =0A= # make the target ellipse=0A= diam =3D r * 2.0=0A= target_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, = edgecolor=3D"darkred" )=0A= ax.add_patch( target_ellipse )=0A= =0A= # make the upper-bound ellipse=0A= diam =3D (r + delta) * 2.0=0A= upper_ellipse =3D Ellipse( (0.0, 0.0), diam, diam, 0.0, fill=3DFalse, = edgecolor=3D"darkblue" )=0A= ax.add_patch( upper_ellipse )=0A= =0A= # make the target=0A= diam =3D delta * 2.0=0A= target =3D Ellipse( (x, y), diam, diam, 0.0, fill=3DFalse, = edgecolor=3D"#DD1208" )=0A= ax.add_patch( target )=0A= =0A= # give it a big marker=0A= ax.plot( [x], [y], marker=3D'x', linestyle=3D'None', mfc=3D'red', = mec=3D'red', markersize=3D10 )=0A= =0A= ##################################################=0A= # now lets do the same thing again using a custom ellipse function=0A= =0A= # make the axes=0A= ax =3D subplot( 212, aspect=3D'equal', sharex=3Dax, sharey=3Dax )=0A= ax.set_aspect( 'equal', 'datalim' )=0A= =0A= # make the lower-bound ellipse=0A= custom_ellipse( ax, 0.0, 0.0, r-delta, r-delta, 0.0, color=3D"darkgreen" = )=0A= =0A= # make the target ellipse=0A= custom_ellipse( ax, 0.0, 0.0, r, r, 0.0, color=3D"darkred" )=0A= =0A= # make the upper-bound ellipse=0A= custom_ellipse( ax, 0.0, 0.0, r+delta, r+delta, 0.0, color=3D"darkblue" )=0A= =0A= # make the target=0A= custom_ellipse( ax, x, y, delta, delta, 0.0, color=3D"#BB1208" )=0A= =0A= # give it a big marker=0A= ax.plot( [x], [y], marker=3D'x', linestyle=3D'None', mfc=3D'red', = mec=3D'red', markersize=3D10 )=0A= =0A= ##################################################=0A= # lets zoom in to see the area of interest=0A= =0A= ax.set_xlim(2650, 2735)=0A= ax.set_ylim(6705, 6735)=0A= show()=0A= =0A= ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: John Hunter - 2007-12-08 14:10:05 ```On Dec 7, 2007 6:02 PM, James Evans wrote: > There appears to be an issue with the agg backend with how it is drawing > ellipses (or maybe it is how matplotlib uses agg), but the attached script > shows how a point, which should be coincident with the center circle, but it > is not. The second plot shows the same data, but using a custom (and much > slower) algorithm for drawing the ellipses, where the point is properly > coincident. Thanks for the test case James -- I will try and sort this out ASAP. Michael, do you see the same on the transforms branch? The branch is on a newer version of agg so if not, perhaps it is a simple matter of upgrading agg on the trunk. I'm travelling currently bt will be back omorrow and ill look at this ASAP. JDH ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Charlie Moad - 2007-12-09 15:11:17 ```I found a great doc I am linking. The 4 spline method we are using has an error tolerance of 2.7*10^-4, which I am pretty sure is coming into play here. If we move to an 8 spline approach, it would reduce the error a few orders of magnitude. http://www.tinaja.com/glib/ellipse4.pdf - Charlie On Dec 8, 2007 9:09 AM, John Hunter wrote: > On Dec 7, 2007 6:02 PM, James Evans wrote: > > > There appears to be an issue with the agg backend with how it is drawing > > ellipses (or maybe it is how matplotlib uses agg), but the attached script > > shows how a point, which should be coincident with the center circle, but it > > is not. The second plot shows the same data, but using a custom (and much > > slower) algorithm for drawing the ellipses, where the point is properly > > coincident. > > Thanks for the test case James -- I will try and sort this out ASAP. > Michael, do you see the same on the transforms branch? The branch is > on a newer version of agg so if not, perhaps it is a simple matter of > upgrading agg on the trunk. I'm travelling currently bt will be back > omorrow and ill look at this ASAP. > > JDH > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://sourceforge.net/services/buy/index.php > _______________________________________________ > Matplotlib-devel mailing list > Matplotlib-devel@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Charlie Moad - 2007-12-09 16:49:45 ```I did some more digging and it looks like this changed with the transforms. curve4 is now being called instead of arc_to, which uses beziers. On Dec 9, 2007 10:11 AM, Charlie Moad wrote: > I found a great doc I am linking. The 4 spline method we are using > has an error tolerance of 2.7*10^-4, which I am pretty sure is coming > into play here. If we move to an 8 spline approach, it would reduce > the error a few orders of magnitude. > > http://www.tinaja.com/glib/ellipse4.pdf > > - Charlie > > > > On Dec 8, 2007 9:09 AM, John Hunter wrote: > > On Dec 7, 2007 6:02 PM, James Evans wrote: > > > > > There appears to be an issue with the agg backend with how it is drawing > > > ellipses (or maybe it is how matplotlib uses agg), but the attached script > > > shows how a point, which should be coincident with the center circle, but it > > > is not. The second plot shows the same data, but using a custom (and much > > > slower) algorithm for drawing the ellipses, where the point is properly > > > coincident. > > > > Thanks for the test case James -- I will try and sort this out ASAP. > > Michael, do you see the same on the transforms branch? The branch is > > on a newer version of agg so if not, perhaps it is a simple matter of > > upgrading agg on the trunk. I'm travelling currently bt will be back > > omorrow and ill look at this ASAP. > > > > JDH > > > > ------------------------------------------------------------------------- > > SF.Net email is sponsored by: > > Check out the new SourceForge.net Marketplace. > > It's the best place to buy or sell services for > > just about anything Open Source. > > http://sourceforge.net/services/buy/index.php > > _______________________________________________ > > Matplotlib-devel mailing list > > Matplotlib-devel@... > > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > > > ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-10 14:02:45 ```Charlie Moad wrote: > I did some more digging and it looks like this changed with the > transforms. curve4 is now being called instead of arc_to, which uses > beziers. curve4 is the way to specify a cubic bezier curve, so it is functionally equivalent to the old arc_to approach (but easier to be consistent across backends, which is why the change was made). I'm attempting to implement the 8-spline approximation and I'll let you know how that goes. In any case, I think we should add James' example to our unit tests, since it illustrates a case where my assumptions about how ellipses would be used breaks down. Cheers, Mike > On Dec 9, 2007 10:11 AM, Charlie Moad wrote: >> I found a great doc I am linking. The 4 spline method we are using >> has an error tolerance of 2.7*10^-4, which I am pretty sure is coming >> into play here. If we move to an 8 spline approach, it would reduce >> the error a few orders of magnitude. >> >> http://www.tinaja.com/glib/ellipse4.pdf >> >> - Charlie >> >> >> >> On Dec 8, 2007 9:09 AM, John Hunter wrote: >>> On Dec 7, 2007 6:02 PM, James Evans wrote: >>> >>>> There appears to be an issue with the agg backend with how it is drawing >>>> ellipses (or maybe it is how matplotlib uses agg), but the attached script >>>> shows how a point, which should be coincident with the center circle, but it >>>> is not. The second plot shows the same data, but using a custom (and much >>>> slower) algorithm for drawing the ellipses, where the point is properly >>>> coincident. >>> Thanks for the test case James -- I will try and sort this out ASAP. >>> Michael, do you see the same on the transforms branch? The branch is >>> on a newer version of agg so if not, perhaps it is a simple matter of >>> upgrading agg on the trunk. I'm travelling currently bt will be back >>> omorrow and ill look at this ASAP. >>> >>> JDH >>> >>> ------------------------------------------------------------------------- >>> SF.Net email is sponsored by: >>> Check out the new SourceForge.net Marketplace. >>> It's the best place to buy or sell services for >>> just about anything Open Source. >>> http://sourceforge.net/services/buy/index.php >>> _______________________________________________ >>> Matplotlib-devel mailing list >>> Matplotlib-devel@... >>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >>> > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://sourceforge.net/services/buy/index.php > _______________________________________________ > Matplotlib-devel mailing list > Matplotlib-devel@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-10 14:51:45 ```Michael Droettboom wrote: > Charlie Moad wrote: >> I did some more digging and it looks like this changed with the >> transforms. curve4 is now being called instead of arc_to, which uses >> beziers. > > curve4 is the way to specify a cubic bezier curve, so it is functionally > equivalent to the old arc_to approach (but easier to be consistent > across backends, which is why the change was made). Sorry, I was confused... John recently fixed the ellipse drawing on the trunk (which was broken wrt rotated ellipses), to use bezier curves instead of agg's arc_to. Agg's arc_to itself isn't broken wrt to James' problem -- in fact it does provide sufficient accuracy -- it was the way mpl used arc_to in previous incarnations that was broken wrt rotated ellipses. Unfortunately, the fix for that reduced accuracy to noticable levels on these really large ellipses. So, in order to have the best of both worlds, I agree the 8-spline approximation seems like the way to go. (But the changes on the transforms branch are irrelevant here -- they do essentially the same thing the trunk currently does: that is 4 spline approximation of the circle). > I'm attempting to implement the 8-spline approximation and I'll let you > know how that goes. I have 8-spline approximation working on the trunk and on the transforms branch. (r4679) In the process, I uncovered another bug (which I suppose should have been obvious when ellipses were updated last time, but went right by me) -- ellipses don't work at all in the pdf, svg or cairo backends, since they don't implement draw_path. I'll file a placeholder bug for this, and hopefully get to it, time permitting. > In any case, I think we should add James' example > to our unit tests, since it illustrates a case where my assumptions > about how ellipses would be used breaks down. Also done. Cheers, Mike >> On Dec 9, 2007 10:11 AM, Charlie Moad wrote: >>> I found a great doc I am linking. The 4 spline method we are using >>> has an error tolerance of 2.7*10^-4, which I am pretty sure is coming >>> into play here. If we move to an 8 spline approach, it would reduce >>> the error a few orders of magnitude. >>> >>> http://www.tinaja.com/glib/ellipse4.pdf >>> >>> - Charlie >>> >>> >>> >>> On Dec 8, 2007 9:09 AM, John Hunter wrote: >>>> On Dec 7, 2007 6:02 PM, James Evans wrote: >>>> >>>>> There appears to be an issue with the agg backend with how it is drawing >>>>> ellipses (or maybe it is how matplotlib uses agg), but the attached script >>>>> shows how a point, which should be coincident with the center circle, but it >>>>> is not. The second plot shows the same data, but using a custom (and much >>>>> slower) algorithm for drawing the ellipses, where the point is properly >>>>> coincident. >>>> Thanks for the test case James -- I will try and sort this out ASAP. >>>> Michael, do you see the same on the transforms branch? The branch is >>>> on a newer version of agg so if not, perhaps it is a simple matter of >>>> upgrading agg on the trunk. I'm travelling currently bt will be back >>>> omorrow and ill look at this ASAP. >>>> >>>> JDH >>>> >>>> ------------------------------------------------------------------------- >>>> SF.Net email is sponsored by: >>>> Check out the new SourceForge.net Marketplace. >>>> It's the best place to buy or sell services for >>>> just about anything Open Source. >>>> http://sourceforge.net/services/buy/index.php >>>> _______________________________________________ >>>> Matplotlib-devel mailing list >>>> Matplotlib-devel@... >>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >>>> >> ------------------------------------------------------------------------- >> SF.Net email is sponsored by: >> Check out the new SourceForge.net Marketplace. >> It's the best place to buy or sell services for >> just about anything Open Source. >> http://sourceforge.net/services/buy/index.php >> _______________________________________________ >> Matplotlib-devel mailing list >> Matplotlib-devel@... >> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: John Hunter - 2007-12-10 15:12:31 ```On Dec 10, 2007 8:51 AM, Michael Droettboom wrote: > I have 8-spline approximation working on the trunk and on the transforms > branch. (r4679) Thanks Michael, I was working on this myself but it is hard for me to keep up with you :-) In reading the paper Charlie sent and links therein (http://www.tinaja.com/glib/ellipse4.pdf and http://itc.ktu.lt/itc354/Riskus354.pdf), one comment was that the usual magic number offset = 4.0 * (npy.sqrt(2) - 1) / 3.0 is not ideal. When I tested the JPLs test script with one of the suggested magic numbers which minimize the SS errors with 4 points on the ellipse, the error was smaller than what we were getting with the one above (I used k=0.55191496 from the Rivus paper). I see you are using a different formula for the magic number in the trunk. Do you think we could see additional accuracy with a different magic number as discussed in these papers? JDH ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-10 15:26:46 ```John Hunter wrote: > On Dec 10, 2007 8:51 AM, Michael Droettboom wrote: > >> I have 8-spline approximation working on the trunk and on the transforms >> branch. (r4679) > > Thanks Michael, I was working on this myself but it is hard for me to > keep up with you :-) No problem. I wasn't sure if you were still on vacation... Feel free to replace mine with whatever you came up with if you see further benefit. > In reading the paper Charlie sent and links therein > (http://www.tinaja.com/glib/ellipse4.pdf and > http://itc.ktu.lt/itc354/Riskus354.pdf), one comment was that the > usual magic number > > offset = 4.0 * (npy.sqrt(2) - 1) / 3.0 > > is not ideal. When I tested the JPLs test script with one of the > suggested magic numbers which minimize the SS errors with 4 points on > the ellipse, the error was smaller than what we were getting with the > one above (I used k=0.55191496 from the Rivus paper). The first thing I tried when I saw Lancaster's paper (from Charlie's e-mail) was to leave it as four splines and use his suggested number of 0.551784. That improved things for James' example, but not nearly enough. There were still around 10 pixels between where the ellipses should be and where they were. It's possible that an even better magic number exists (I gather Lancaster's was arrived at by experimentation), but I was doubtful that one could be found that would be as good as just going to 8 splines. > I see you are > using a different formula for the magic number in the trunk. Do you > think we could see additional accuracy with a different magic number > as discussed in these papers? For the 8 spline approximation I put in the trunk this morning, I used Lancaster's suggested magic number of 0.2652031. (MAGIC45 is just the rectilinear distance of the MAGIC number at a 45 degree angle). Again, feel free to tinker, but that number seemed "good enough" on James' example. Cheers, Mike -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Ted Drain - 2007-12-10 16:25:31 ```Everyone, Before someone spends a lot of time re-working the ellipse code to add more splines, I think we should talk about the problem and maybe consider another approach. The real problem w/ this for us is that we plot a lot of things at interplanetary scales (millions of kilometers). Even 1e-6 accuracy is still a miss of a kilometer (assuming that error tolerance is related to r). What we really need is something that is viewport (i.e. the data range being currently viewed) dependent. The errors for the 4 spline case are fine as long as it's a spline through 4 points that are in the viewport window. So if I have an ellipse that's 3 million by 5 million and I'm viewing the whole thing on a plot, 1e-4 of 3e6 is fine. However, if I've zoomed in to a portion of the ellipse and my current axes bounds are 10 km x 10 km, then 1e-4 isn't fine AND 1e-6 isn't fine either. If we could recompute the curve based on the current zoom level, then 1e-4 is fine again. One way to think about this is as error in pixels (since that's what the user is actually looking at). It would be nice if the pixel error could be held constant. Let's say that one pixel is the error we're going for. Any system that gives a one pixel error at arbitrary zoom levels is the way to go. A system with an error expressed in data coordinates will always have problems at some arbitrary zoom level. I don't know if the current MPL architecture can support this but it would be nice if it worked that way. We have people making decisions based on what these plots show that affect spacecraft worth hundreds of millions of dollars so it's important that we're plotting things accurately. Ted At 07:26 AM 12/10/2007, Michael Droettboom wrote: >John Hunter wrote: > > On Dec 10, 2007 8:51 AM, Michael Droettboom wrote: > > > >> I have 8-spline approximation working on the trunk and on the transforms > >> branch. (r4679) > > > > Thanks Michael, I was working on this myself but it is hard for me to > > keep up with you :-) > >No problem. I wasn't sure if you were still on vacation... Feel free >to replace mine with whatever you came up with if you see further benefit. > > > In reading the paper Charlie sent and links therein > > ( and>http://www.tinaja.com/glib/ellipse4.pdf and > > http://itc.ktu.lt/itc354/Riskus354.pdf), one comment was that the > > usual magic number > > > > offset = 4.0 * (npy.sqrt(2) - 1) / 3.0 > > > > is not ideal. When I tested the JPLs test script with one of the > > suggested magic numbers which minimize the SS errors with 4 points on > > the ellipse, the error was smaller than what we were getting with the > > one above (I used k=0.55191496 from the Rivus paper). > >The first thing I tried when I saw Lancaster's paper (from Charlie's >e-mail) was to leave it as four splines and use his suggested number of >0.551784. That improved things for James' example, but not nearly >enough. There were still around 10 pixels between where the ellipses >should be and where they were. It's possible that an even better magic >number exists (I gather Lancaster's was arrived at by experimentation), >but I was doubtful that one could be found that would be as good as just >going to 8 splines. > > > I see you are > > using a different formula for the magic number in the trunk. Do you > > think we could see additional accuracy with a different magic number > > as discussed in these papers? > >For the 8 spline approximation I put in the trunk this morning, I used >Lancaster's suggested magic number of 0.2652031. (MAGIC45 is just the >rectilinear distance of the MAGIC number at a 45 degree angle). Again, >feel free to tinker, but that number seemed "good enough" on James' example. > >Cheers, >Mike > >-- >Michael Droettboom >Science Software Branch >Operations and Engineering Division >Space Telescope Science Institute >Operated by AURA for NASA > >------------------------------------------------------------------------- >SF.Net email is sponsored by: >Check out the new SourceForge.net Marketplace. >It's the best place to buy or sell services for >just about anything Open Source. >http://sourceforge.net/services/buy/index.php >_______________________________________________ >Matplotlib-devel mailing list >Matplotlib-devel@... >https://lists.sourceforge.net/lists/listinfo/matplotlib-devel Ted Drain Jet Propulsion Laboratory ted.drain@... ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: John Hunter - 2007-12-10 16:36:02 ```On Dec 10, 2007 10:25 AM, Ted Drain wrote: > I don't know if the current MPL architecture can support this but it > would be nice if it worked that way. We have people making decisions > based on what these plots show that affect spacecraft worth hundreds > of millions of dollars so it's important that we're plotting things accurately. We can support this, but I think we would do this with an arc class rather than an ellipse class, and write a special case class that is viewlim aware. A simple example of a line that has analogous behavior is examples/clippedline.py, which clips the points outside the viewport and draws in a different style according to the resolution of the viewlim. The reason I think it would be preferable to use an arc here is because we won't have to worry about filling the thing when we only approximate a section of it. You could feed in a 360 degree elliptical arc and then zoom into a portion of it. With the 8 point ellipse as is, and the addition of an arc class that does 4 or 8 point approximation within the zoom limits, should that serve your requirements? JDH ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-10 16:53:58 ```John Hunter wrote: > On Dec 10, 2007 10:25 AM, Ted Drain wrote: > >> I don't know if the current MPL architecture can support this but it >> would be nice if it worked that way. We have people making decisions >> based on what these plots show that affect spacecraft worth hundreds >> of millions of dollars so it's important that we're plotting things accurately. > > We can support this, but I think we would do this with an arc class > rather than an ellipse class, and write a special case class that is > viewlim aware. I agree -- I think there are two uses cases for ellipse that are in conflict here. One is these large ellipses, the other is for things like scatter plots, where speed and file size is more important than accuracy. My mind was probably stuck on the latter as I've worked along the transforms branch. > A simple example of a line that has analogous > behavior is examples/clippedline.py, which clips the points outside > the viewport and draws in a different style according to the > resolution of the viewlim. The reason I think it would be preferable > to use an arc here is because we won't have to worry about filling the > thing when we only approximate a section of it. You could feed in a > 360 degree elliptical arc and then zoom into a portion of it. > > With the 8 point ellipse as is, and the addition of an arc class that > does 4 or 8 point approximation within the zoom limits, should that > serve your requirements? As a possible starting point, the transforms branch already has arc-approximation-by-cubic-bezier-spline code. It determines the number of splines to use based on the radians included in the arc, which is clearly not what we want here. But it should be reasonably straightforward to make that some fixed number and draw the arc between the edges of the axes. Or, alternatively, (and maybe this is what John is suggesting), the arc could be approximated by line segments (with the number of segments something like the number of pixels across the axes). To my naive mind, that seems more verifiable -- or at least it puts the responsibility of getting this right all in one place. IMHO, these spline approximation tricks are all just with the aim of pushing curve rendering deeper into the backends for speed and file size improvements. But obviously there needs to be a way around it when it matters. Cheers, Mike -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Ted Drain - 2007-12-10 17:35:00 ```All of these sound like good ideas to me. Just for some history: the original reason we worked w/ John to get an Ellipse primitive in (vs a normal line plot of sampled points) were to: - improve ellipse plotting speeds (we plot a LOT of them at once) - improve post script output Ted At 08:53 AM 12/10/2007, Michael Droettboom wrote: >John Hunter wrote: > > On Dec 10, 2007 10:25 AM, Ted Drain wrote: > > > >> I don't know if the current MPL architecture can support this but it > >> would be nice if it worked that way. We have people making decisions > >> based on what these plots show that affect spacecraft worth hundreds > >> of millions of dollars so it's important that we're plotting > things accurately. > > > > We can support this, but I think we would do this with an arc class > > rather than an ellipse class, and write a special case class that is > > viewlim aware. > >I agree -- I think there are two uses cases for ellipse that are in >conflict here. One is these large ellipses, the other is for things >like scatter plots, where speed and file size is more important than >accuracy. My mind was probably stuck on the latter as I've worked along >the transforms branch. > > > A simple example of a line that has analogous > > behavior is examples/clippedline.py, which clips the points outside > > the viewport and draws in a different style according to the > > resolution of the viewlim. The reason I think it would be preferable > > to use an arc here is because we won't have to worry about filling the > > thing when we only approximate a section of it. You could feed in a > > 360 degree elliptical arc and then zoom into a portion of it. > > > > With the 8 point ellipse as is, and the addition of an arc class that > > does 4 or 8 point approximation within the zoom limits, should that > > serve your requirements? > >As a possible starting point, the transforms branch already has >arc-approximation-by-cubic-bezier-spline code. It determines the number >of splines to use based on the radians included in the arc, which is >clearly not what we want here. But it should be reasonably >straightforward to make that some fixed number and draw the arc between >the edges of the axes. Or, alternatively, (and maybe this is what John >is suggesting), the arc could be approximated by line segments (with the >number of segments something like the number of pixels across the axes). > To my naive mind, that seems more verifiable -- or at least it puts >the responsibility of getting this right all in one place. > >IMHO, these spline approximation tricks are all just with the aim of >pushing curve rendering deeper into the backends for speed and file size >improvements. But obviously there needs to be a way around it when it >matters. > >Cheers, >Mike > >-- >Michael Droettboom >Science Software Branch >Operations and Engineering Division >Space Telescope Science Institute >Operated by AURA for NASA > >------------------------------------------------------------------------- >SF.Net email is sponsored by: >Check out the new SourceForge.net Marketplace. >It's the best place to buy or sell services for >just about anything Open Source. >http://sourceforge.net/services/buy/index.php >_______________________________________________ >Matplotlib-devel mailing list >Matplotlib-devel@... >https://lists.sourceforge.net/lists/listinfo/matplotlib-devel Ted Drain Jet Propulsion Laboratory ted.drain@... ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-11 20:43:44 Attachments: ellipse.png ```I have a working draft of something that may work for this problem on the transforms branch. I am happy to backport this to the trunk, but that will require some effort, as the implementation relies on many of the new geometric utilities on the branch that would also have to be brought over. It may be some time until the branch is ready for production use, but if you are able to use it to experiment with this approach to this specific problem, that would certainly make my life easier, so I don't have to do the backporting work more than once. Attached is a plot comparing the new approach (above) vs. a 750-edge polygonal approximation for the ellipses (based directly on James Evans' example). Here's a description of what it does: Ellipses are normally drawn using an approximation that uses eight cubic bezier splines. The error of this approximation is 1.89818e-6, according to this unverified source: Lancaster, Don. Approximating a Circle or an Ellipse Using Four Bezier Cubic Splines. http://www.tinaja.com/glib/ellipse4.pdf There is a use case where very large ellipses must be drawn with very high accuracy, and it is too expensive to render the entire ellipse with enough segments (either splines or line segments). Therefore, in the case where either radius of the ellipse is large enough that the error of the spline approximation will be visible (greater than one pixel offset from the ideal), a different technique is used. In that case, only the visible parts of the ellipse are drawn, with each visible arc using a fixed number of spline segments (8). The algorithm proceeds as follows: 1. The points where the ellipse intersects the axes bounding box are located. (This is done be performing an inverse transformation on the axes bbox such that it is relative to the unit circle -- this makes the intersection calculation much easier than doing rotated ellipse intersection directly). This uses the "line intersecting a circle" algorithm from: Vince, John. Geometry for Computer Graphics: Formulae, Examples & Proofs. London: Springer-Verlag, 2005. 2. The angles of each of the intersection points are calculated. 3. Proceeding counterclockwise starting in the positive x-direction, each of the visible arc-segments between the pairs of vertices are drawn using the bezier arc approximation technique implemented in Path.arc(). Cheers, Mike Ted Drain wrote: > All of these sound like good ideas to me. Just for some history: the > original reason we worked w/ John to get an Ellipse primitive in (vs > a normal line plot of sampled points) were to: > - improve ellipse plotting speeds (we plot a LOT of them at once) > - improve post script output > > Ted > > At 08:53 AM 12/10/2007, Michael Droettboom wrote: >> John Hunter wrote: >>> On Dec 10, 2007 10:25 AM, Ted Drain wrote: >>> >>>> I don't know if the current MPL architecture can support this but it >>>> would be nice if it worked that way. We have people making decisions >>>> based on what these plots show that affect spacecraft worth hundreds >>>> of millions of dollars so it's important that we're plotting >> things accurately. >>> We can support this, but I think we would do this with an arc class >>> rather than an ellipse class, and write a special case class that is >>> viewlim aware. >> I agree -- I think there are two uses cases for ellipse that are in >> conflict here. One is these large ellipses, the other is for things >> like scatter plots, where speed and file size is more important than >> accuracy. My mind was probably stuck on the latter as I've worked along >> the transforms branch. >> >>> A simple example of a line that has analogous >>> behavior is examples/clippedline.py, which clips the points outside >>> the viewport and draws in a different style according to the >>> resolution of the viewlim. The reason I think it would be preferable >>> to use an arc here is because we won't have to worry about filling the >>> thing when we only approximate a section of it. You could feed in a >>> 360 degree elliptical arc and then zoom into a portion of it. >>> >>> With the 8 point ellipse as is, and the addition of an arc class that >>> does 4 or 8 point approximation within the zoom limits, should that >>> serve your requirements? >> As a possible starting point, the transforms branch already has >> arc-approximation-by-cubic-bezier-spline code. It determines the number >> of splines to use based on the radians included in the arc, which is >> clearly not what we want here. But it should be reasonably >> straightforward to make that some fixed number and draw the arc between >> the edges of the axes. Or, alternatively, (and maybe this is what John >> is suggesting), the arc could be approximated by line segments (with the >> number of segments something like the number of pixels across the axes). >> To my naive mind, that seems more verifiable -- or at least it puts >> the responsibility of getting this right all in one place. >> >> IMHO, these spline approximation tricks are all just with the aim of >> pushing curve rendering deeper into the backends for speed and file size >> improvements. But obviously there needs to be a way around it when it >> matters. >> >> Cheers, >> Mike >> >> -- >> Michael Droettboom >> Science Software Branch >> Operations and Engineering Division >> Space Telescope Science Institute >> Operated by AURA for NASA >> >> ------------------------------------------------------------------------- >> SF.Net email is sponsored by: >> Check out the new SourceForge.net Marketplace. >> It's the best place to buy or sell services for >> just about anything Open Source. >> http://sourceforge.net/services/buy/index.php >> _______________________________________________ >> Matplotlib-devel mailing list >> Matplotlib-devel@... >> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > > Ted Drain Jet Propulsion Laboratory ted.drain@... > > > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://sourceforge.net/services/buy/index.php > _______________________________________________ > Matplotlib-devel mailing list > Matplotlib-devel@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-11 20:46:29 Attachments: ellipse.png ```Sorry -- correct attachment this time. Michael Droettboom wrote: > I have a working draft of something that may work for this problem on > the transforms branch. I am happy to backport this to the trunk, but > that will require some effort, as the implementation relies on many of > the new geometric utilities on the branch that would also have to be > brought over. It may be some time until the branch is ready for > production use, but if you are able to use it to experiment with this > approach to this specific problem, that would certainly make my life > easier, so I don't have to do the backporting work more than once. > > Attached is a plot comparing the new approach (above) vs. a 750-edge > polygonal approximation for the ellipses (based directly on James Evans' > example). Here's a description of what it does: > > > Ellipses are normally drawn using an approximation that uses > eight cubic bezier splines. The error of this approximation > is 1.89818e-6, according to this unverified source: > > Lancaster, Don. Approximating a Circle or an Ellipse Using > Four Bezier Cubic Splines. > > http://www.tinaja.com/glib/ellipse4.pdf > > There is a use case where very large ellipses must be drawn > with very high accuracy, and it is too expensive to render the > entire ellipse with enough segments (either splines or line > segments). Therefore, in the case where either radius of the > ellipse is large enough that the error of the spline > approximation will be visible (greater than one pixel offset > from the ideal), a different technique is used. > > In that case, only the visible parts of the ellipse are drawn, > with each visible arc using a fixed number of spline segments > (8). The algorithm proceeds as follows: > > 1. The points where the ellipse intersects the axes bounding > box are located. (This is done be performing an inverse > transformation on the axes bbox such that it is relative to > the unit circle -- this makes the intersection calculation > much easier than doing rotated ellipse intersection > directly). > > This uses the "line intersecting a circle" algorithm from: > > Vince, John. Geometry for Computer Graphics: Formulae, > Examples & Proofs. London: Springer-Verlag, 2005. > > 2. The angles of each of the intersection points are > calculated. > > 3. Proceeding counterclockwise starting in the positive > x-direction, each of the visible arc-segments between the > pairs of vertices are drawn using the bezier arc > approximation technique implemented in Path.arc(). > > > Cheers, > Mike > > > Ted Drain wrote: >> All of these sound like good ideas to me. Just for some history: the >> original reason we worked w/ John to get an Ellipse primitive in (vs a >> normal line plot of sampled points) were to: >> - improve ellipse plotting speeds (we plot a LOT of them at once) >> - improve post script output >> >> Ted >> >> At 08:53 AM 12/10/2007, Michael Droettboom wrote: >>> John Hunter wrote: >>>> On Dec 10, 2007 10:25 AM, Ted Drain wrote: >>>> >>>>> I don't know if the current MPL architecture can support this but it >>>>> would be nice if it worked that way. We have people making decisions >>>>> based on what these plots show that affect spacecraft worth hundreds >>>>> of millions of dollars so it's important that we're plotting >>> things accurately. >>>> We can support this, but I think we would do this with an arc class >>>> rather than an ellipse class, and write a special case class that is >>>> viewlim aware. >>> I agree -- I think there are two uses cases for ellipse that are in >>> conflict here. One is these large ellipses, the other is for things >>> like scatter plots, where speed and file size is more important than >>> accuracy. My mind was probably stuck on the latter as I've worked along >>> the transforms branch. >>> >>>> A simple example of a line that has analogous >>>> behavior is examples/clippedline.py, which clips the points outside >>>> the viewport and draws in a different style according to the >>>> resolution of the viewlim. The reason I think it would be preferable >>>> to use an arc here is because we won't have to worry about filling the >>>> thing when we only approximate a section of it. You could feed in a >>>> 360 degree elliptical arc and then zoom into a portion of it. >>>> >>>> With the 8 point ellipse as is, and the addition of an arc class that >>>> does 4 or 8 point approximation within the zoom limits, should that >>>> serve your requirements? >>> As a possible starting point, the transforms branch already has >>> arc-approximation-by-cubic-bezier-spline code. It determines the number >>> of splines to use based on the radians included in the arc, which is >>> clearly not what we want here. But it should be reasonably >>> straightforward to make that some fixed number and draw the arc between >>> the edges of the axes. Or, alternatively, (and maybe this is what John >>> is suggesting), the arc could be approximated by line segments (with the >>> number of segments something like the number of pixels across the axes). >>> To my naive mind, that seems more verifiable -- or at least it puts >>> the responsibility of getting this right all in one place. >>> >>> IMHO, these spline approximation tricks are all just with the aim of >>> pushing curve rendering deeper into the backends for speed and file size >>> improvements. But obviously there needs to be a way around it when it >>> matters. >>> >>> Cheers, >>> Mike >>> >>> -- >>> Michael Droettboom >>> Science Software Branch >>> Operations and Engineering Division >>> Space Telescope Science Institute >>> Operated by AURA for NASA >>> >>> ------------------------------------------------------------------------- >>> >>> SF.Net email is sponsored by: >>> Check out the new SourceForge.net Marketplace. >>> It's the best place to buy or sell services for >>> just about anything Open Source. >>> http://sourceforge.net/services/buy/index.php >>> _______________________________________________ >>> Matplotlib-devel mailing list >>> Matplotlib-devel@... >>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >> >> Ted Drain Jet Propulsion Laboratory ted.drain@... >> >> >> ------------------------------------------------------------------------- >> SF.Net email is sponsored by: Check out the new SourceForge.net >> Marketplace. >> It's the best place to buy or sell services for >> just about anything Open Source. >> http://sourceforge.net/services/buy/index.php >> _______________________________________________ >> Matplotlib-devel mailing list >> Matplotlib-devel@... >> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > > > ------------------------------------------------------------------------ > > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://sourceforge.net/services/buy/index.php > > > ------------------------------------------------------------------------ > > _______________________________________________ > Matplotlib-devel mailing list > Matplotlib-devel@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Michael Droettboom - 2007-12-11 20:48:01 Attachments: ellipse.png ```And an actually interesting part of the plot... ;) Michael Droettboom wrote: > Sorry -- correct attachment this time. > > Michael Droettboom wrote: >> I have a working draft of something that may work for this problem on >> the transforms branch. I am happy to backport this to the trunk, but >> that will require some effort, as the implementation relies on many of >> the new geometric utilities on the branch that would also have to be >> brought over. It may be some time until the branch is ready for >> production use, but if you are able to use it to experiment with this >> approach to this specific problem, that would certainly make my life >> easier, so I don't have to do the backporting work more than once. >> >> Attached is a plot comparing the new approach (above) vs. a 750-edge >> polygonal approximation for the ellipses (based directly on James >> Evans' example). Here's a description of what it does: >> >> >> Ellipses are normally drawn using an approximation that uses >> eight cubic bezier splines. The error of this approximation >> is 1.89818e-6, according to this unverified source: >> >> Lancaster, Don. Approximating a Circle or an Ellipse Using >> Four Bezier Cubic Splines. >> >> http://www.tinaja.com/glib/ellipse4.pdf >> >> There is a use case where very large ellipses must be drawn >> with very high accuracy, and it is too expensive to render the >> entire ellipse with enough segments (either splines or line >> segments). Therefore, in the case where either radius of the >> ellipse is large enough that the error of the spline >> approximation will be visible (greater than one pixel offset >> from the ideal), a different technique is used. >> >> In that case, only the visible parts of the ellipse are drawn, >> with each visible arc using a fixed number of spline segments >> (8). The algorithm proceeds as follows: >> >> 1. The points where the ellipse intersects the axes bounding >> box are located. (This is done be performing an inverse >> transformation on the axes bbox such that it is relative to >> the unit circle -- this makes the intersection calculation >> much easier than doing rotated ellipse intersection >> directly). >> >> This uses the "line intersecting a circle" algorithm from: >> >> Vince, John. Geometry for Computer Graphics: Formulae, >> Examples & Proofs. London: Springer-Verlag, 2005. >> >> 2. The angles of each of the intersection points are >> calculated. >> >> 3. Proceeding counterclockwise starting in the positive >> x-direction, each of the visible arc-segments between the >> pairs of vertices are drawn using the bezier arc >> approximation technique implemented in Path.arc(). >> >> >> Cheers, >> Mike >> >> >> Ted Drain wrote: >>> All of these sound like good ideas to me. Just for some history: the >>> original reason we worked w/ John to get an Ellipse primitive in (vs >>> a normal line plot of sampled points) were to: >>> - improve ellipse plotting speeds (we plot a LOT of them at once) >>> - improve post script output >>> >>> Ted >>> >>> At 08:53 AM 12/10/2007, Michael Droettboom wrote: >>>> John Hunter wrote: >>>>> On Dec 10, 2007 10:25 AM, Ted Drain wrote: >>>>> >>>>>> I don't know if the current MPL architecture can support this but it >>>>>> would be nice if it worked that way. We have people making decisions >>>>>> based on what these plots show that affect spacecraft worth hundreds >>>>>> of millions of dollars so it's important that we're plotting >>>> things accurately. >>>>> We can support this, but I think we would do this with an arc class >>>>> rather than an ellipse class, and write a special case class that is >>>>> viewlim aware. >>>> I agree -- I think there are two uses cases for ellipse that are in >>>> conflict here. One is these large ellipses, the other is for things >>>> like scatter plots, where speed and file size is more important than >>>> accuracy. My mind was probably stuck on the latter as I've worked >>>> along >>>> the transforms branch. >>>> >>>>> A simple example of a line that has analogous >>>>> behavior is examples/clippedline.py, which clips the points outside >>>>> the viewport and draws in a different style according to the >>>>> resolution of the viewlim. The reason I think it would be preferable >>>>> to use an arc here is because we won't have to worry about filling the >>>>> thing when we only approximate a section of it. You could feed in a >>>>> 360 degree elliptical arc and then zoom into a portion of it. >>>>> >>>>> With the 8 point ellipse as is, and the addition of an arc class that >>>>> does 4 or 8 point approximation within the zoom limits, should that >>>>> serve your requirements? >>>> As a possible starting point, the transforms branch already has >>>> arc-approximation-by-cubic-bezier-spline code. It determines the >>>> number >>>> of splines to use based on the radians included in the arc, which is >>>> clearly not what we want here. But it should be reasonably >>>> straightforward to make that some fixed number and draw the arc between >>>> the edges of the axes. Or, alternatively, (and maybe this is what John >>>> is suggesting), the arc could be approximated by line segments (with >>>> the >>>> number of segments something like the number of pixels across the >>>> axes). >>>> To my naive mind, that seems more verifiable -- or at least it puts >>>> the responsibility of getting this right all in one place. >>>> >>>> IMHO, these spline approximation tricks are all just with the aim of >>>> pushing curve rendering deeper into the backends for speed and file >>>> size >>>> improvements. But obviously there needs to be a way around it when it >>>> matters. >>>> >>>> Cheers, >>>> Mike >>>> >>>> -- >>>> Michael Droettboom >>>> Science Software Branch >>>> Operations and Engineering Division >>>> Space Telescope Science Institute >>>> Operated by AURA for NASA >>>> >>>> ------------------------------------------------------------------------- >>>> >>>> SF.Net email is sponsored by: >>>> Check out the new SourceForge.net Marketplace. >>>> It's the best place to buy or sell services for >>>> just about anything Open Source. >>>> http://sourceforge.net/services/buy/index.php >>>> _______________________________________________ >>>> Matplotlib-devel mailing list >>>> Matplotlib-devel@... >>>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >>> >>> Ted Drain Jet Propulsion Laboratory ted.drain@... >>> >>> ------------------------------------------------------------------------- >>> >>> SF.Net email is sponsored by: Check out the new SourceForge.net >>> Marketplace. >>> It's the best place to buy or sell services for >>> just about anything Open Source. >>> http://sourceforge.net/services/buy/index.php >>> _______________________________________________ >>> Matplotlib-devel mailing list >>> Matplotlib-devel@... >>> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >> >> >> ------------------------------------------------------------------------ >> >> >> ------------------------------------------------------------------------ >> >> ------------------------------------------------------------------------- >> SF.Net email is sponsored by: Check out the new SourceForge.net >> Marketplace. >> It's the best place to buy or sell services for >> just about anything Open Source. >> http://sourceforge.net/services/buy/index.php >> >> >> ------------------------------------------------------------------------ >> >> _______________________________________________ >> Matplotlib-devel mailing list >> Matplotlib-devel@... >> https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > > > ------------------------------------------------------------------------ > > > ------------------------------------------------------------------------ > > ------------------------------------------------------------------------- > SF.Net email is sponsored by: > Check out the new SourceForge.net Marketplace. > It's the best place to buy or sell services for > just about anything Open Source. > http://sourceforge.net/services/buy/index.php > > > ------------------------------------------------------------------------ > > _______________________________________________ > Matplotlib-devel mailing list > Matplotlib-devel@... > https://lists.sourceforge.net/lists/listinfo/matplotlib-devel -- Michael Droettboom Science Software Branch Operations and Engineering Division Space Telescope Science Institute Operated by AURA for NASA ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: Ted Drain - 2007-12-11 21:25:00 Attachments: Message as HTML ```Michael, Thanks! That looks like a great solution. We'll take a look at it this week and try to beat on it w/ some more test cases. Ted At 12:46 PM 12/11/2007, Michael Droettboom wrote: >Sorry -- correct attachment this time. > >Michael Droettboom wrote: >>I have a working draft of something that may work for this problem >>on the transforms branch. I am happy to backport this to the >>trunk, but that will require some effort, as the implementation >>relies on many of the new geometric utilities on the branch that >>would also have to be brought over. It may be some time until the >>branch is ready for production use, but if you are able to use it >>to experiment with this approach to this specific problem, that >>would certainly make my life easier, so I don't have to do the >>backporting work more than once. >>Attached is a plot comparing the new approach (above) vs. a >>750-edge polygonal approximation for the ellipses (based directly >>on James Evans' example). Here's a description of what it does: >> >> Ellipses are normally drawn using an approximation that uses >> eight cubic bezier splines. The error of this approximation >> is 1.89818e-6, according to this unverified source: >> Lancaster, Don. Approximating a Circle or an Ellipse Using >> Four Bezier Cubic Splines. >> http://www.tinaja.com/glib/ellipse4.pdf >> There is a use case where very large ellipses must be drawn >> with very high accuracy, and it is too expensive to render the >> entire ellipse with enough segments (either splines or line >> segments). Therefore, in the case where either radius of the >> ellipse is large enough that the error of the spline >> approximation will be visible (greater than one pixel offset >> from the ideal), a different technique is used. >> In that case, only the visible parts of the ellipse are drawn, >> with each visible arc using a fixed number of spline segments >> (8). The algorithm proceeds as follows: >> 1. The points where the ellipse intersects the axes bounding >> box are located. (This is done be performing an inverse >> transformation on the axes bbox such that it is relative to >> the unit circle -- this makes the intersection calculation >> much easier than doing rotated ellipse intersection >> directly). >> This uses the "line intersecting a circle" algorithm from: >> Vince, John. Geometry for Computer Graphics: Formulae, >> Examples & Proofs. London: Springer-Verlag, 2005. >> 2. The angles of each of the intersection points are >> calculated. >> 3. Proceeding counterclockwise starting in the positive >> x-direction, each of the visible arc-segments between the >> pairs of vertices are drawn using the bezier arc >> approximation technique implemented in Path.arc(). >> >>Cheers, >>Mike >> >>Ted Drain wrote: >>>All of these sound like good ideas to me. Just for some history: >>>the original reason we worked w/ John to get an Ellipse primitive >>>in (vs a normal line plot of sampled points) were to: >>>- improve ellipse plotting speeds (we plot a LOT of them at once) >>>- improve post script output >>> >>>Ted >>> >>>At 08:53 AM 12/10/2007, Michael Droettboom wrote: >>>>John Hunter wrote: >>>>>On Dec 10, 2007 10:25 AM, Ted Drain wrote: >>>>> >>>>>>I don't know if the current MPL architecture can support this but it >>>>>>would be nice if it worked that way. We have people making decisions >>>>>>based on what these plots show that affect spacecraft worth hundreds >>>>>>of millions of dollars so it's important that we're plotting >>>>things accurately. >>>>>We can support this, but I think we would do this with an arc class >>>>>rather than an ellipse class, and write a special case class that is >>>>>viewlim aware. >>>>I agree -- I think there are two uses cases for ellipse that are in >>>>conflict here. One is these large ellipses, the other is for things >>>>like scatter plots, where speed and file size is more important than >>>>accuracy. My mind was probably stuck on the latter as I've worked along >>>>the transforms branch. >>>> >>>>>A simple example of a line that has analogous >>>>>behavior is examples/clippedline.py, which clips the points outside >>>>>the viewport and draws in a different style according to the >>>>>resolution of the viewlim. The reason I think it would be preferable >>>>>to use an arc here is because we won't have to worry about filling the >>>>>thing when we only approximate a section of it. You could feed in a >>>>>360 degree elliptical arc and then zoom into a portion of it. >>>>> >>>>>With the 8 point ellipse as is, and the addition of an arc class that >>>>>does 4 or 8 point approximation within the zoom limits, should that >>>>>serve your requirements? >>>>As a possible starting point, the transforms branch already has >>>>arc-approximation-by-cubic-bezier-spline code. It determines the number >>>>of splines to use based on the radians included in the arc, which is >>>>clearly not what we want here. But it should be reasonably >>>>straightforward to make that some fixed number and draw the arc between >>>>the edges of the axes. Or, alternatively, (and maybe this is what John >>>>is suggesting), the arc could be approximated by line segments (with the >>>>number of segments something like the number of pixels across the axes). >>>> To my naive mind, that seems more verifiable -- or at least it puts >>>>the responsibility of getting this right all in one place. >>>> >>>>IMHO, these spline approximation tricks are all just with the aim of >>>>pushing curve rendering deeper into the backends for speed and file size >>>>improvements. But obviously there needs to be a way around it when it >>>>matters. >>>> >>>>Cheers, >>>>Mike >>>> >>>>-- >>>>Michael Droettboom >>>>Science Software Branch >>>>Operations and Engineering Division >>>>Space Telescope Science Institute >>>>Operated by AURA for NASA >>>> >>>>------------------------------------------------------------------------- >>>>SF.Net email is sponsored by: >>>>Check out the new SourceForge.net Marketplace. >>>>It's the best place to buy or sell services for >>>>just about anything Open Source. >>>>http://sourceforge.net/services/buy/index.php >>>>_______________________________________________ >>>>Matplotlib-devel mailing list >>>>Matplotlib-devel@... >>>>https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >>> >>>Ted Drain Jet Propulsion Laboratory ted.drain@... >>> >>> >>>------------------------------------------------------------------------- >>>SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. >>>It's the best place to buy or sell services for >>>just about anything Open Source. >>>http://sourceforge.net/services/buy/index.php >>>_______________________________________________ >>>Matplotlib-devel mailing list >>>Matplotlib-devel@... >>>https://lists.sourceforge.net/lists/listinfo/matplotlib-devel >> >>------------------------------------------------------------------------ >> >>------------------------------------------------------------------------ >>------------------------------------------------------------------------- >>SF.Net email is sponsored by: Check out the new SourceForge.net Marketplace. >>It's the best place to buy or sell services for >>just about anything Open Source. >>http://sourceforge.net/services/buy/index.php >> >>------------------------------------------------------------------------ >>_______________________________________________ >>Matplotlib-devel mailing list >>Matplotlib-devel@... >>https://lists.sourceforge.net/lists/listinfo/matplotlib-devel > >-- >Michael Droettboom >Science Software Branch >Operations and Engineering Division >Space Telescope Science Institute >Operated by AURA for NASA > > ```
 Re: [matplotlib-devel] Problem with Agg Ellipses From: John Hunter - 2007-12-11 21:38:58 ```On Dec 11, 2007 3:24 PM, Ted Drain wrote: > Thanks! That looks like a great solution. We'll take a look at it this > week and try to beat on it w/ some more test cases. Very nice work Michael -- I tried updating from your branch but it looks like maybe you haven't committed yet, as the last log entry I am seeing is: r4694 | mdboom | 2007-12-10 13:53:12 -0600 (Mon, 10 Dec 2007) | 2 lines Simplify even more JDH ```