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From: Kevin Karplus <karplus@so...>  20120417 20:51:47

Try http://www.cse.cuhk.edu.hk/~ttwong/papers/udpoint/udpoints.html http://local.wasp.uwa.edu.au/~pbourke/geometry/spherepoints/ http://mathforum.org/kb/thread.jspa?forumID=13&threadID=1248382&messageID=3985254 http://www.mathworks.com/matlabcentral/newsreader/view_thread/21747 Many of these use random points with a uniform distribution on the surface of the sphere, but at least one of them was deterministic. Most of the surface integral calculations I've seen have used sample points, rather than patches. 
From: kirby urner <kirby.urner@gm...>  20120417 18:04:37

> OK, I know, I forgot the octahedron... > Then, the subdivision of the faces you obtain into smaller ones should not > be too difficult. > > Jerzy Karczmarczuk > The triangles of a geodesic sphere e.g. subdivided icosahedron, are not equal area though, not exactly. Maybe exactness is not critical. There are lots of reflections so don't have to compute a full sphere. 1/120th is a common patch to reflect around, based on rhombic triacontahedron breaking into 4 triangles. There's a book coming out any day now, 'Divided Spheres' by Edward Popko that should have a lot of good info. Kirby http://www.amazon.com/DividedSpheresGeodesicsOrderlySubdivision/dp/1466504293 > PS. People who want always have one nice mathematical formula for some > spherical problems too often forget that it is not necessary to have two > singularities at the poles, just one is possible with the stereographic > projection. But the distortions are awful... > > >  > Better than sec? Nothing is better than sec when it comes to > monitoring Big Data applications. Try Boundary onesecond > resolution app monitoring today. Free. > http://p.sf.net/sfu/Boundarydev2dev > _______________________________________________ > Visualpythonusers mailing list > Visualpythonusers@... > https://lists.sourceforge.net/lists/listinfo/visualpythonusers > 
From: Jerzy Karczmarczuk <jerzy.karczmarczuk@un...>  20120417 17:49:46

Joe Heafner: > Can someone direct me to an algorithm for covering a sphere with patches of equal area for the purposes of illustrating the surface integral in Gauss's law? I've tried three so far and can't get good results. The problem is mostly with the poles and in the foreshortening of the patches near the poles. Is there a standard algorithm for this somewhere? Rectangular surfaces are easy. > > Joe Heafner I don't think there is any "standard" algorithm. Perhaps you should have written what DID you try... And, what are your restrictions concerning patches? There are of course some trivial ways. Map into your sphere through the central projection one of the following: 1. A tetrahedron 2. A cube (this is known as the Cobe Sky Cube...) 3. A dodecahedron. Voilà. May I suggest one more? Thanks... 4. An icosahedron... (http://space.mit.edu/home/tegmark/icosahedron.gif) OK, I know, I forgot the octahedron... Then, the subdivision of the faces you obtain into smaller ones should not be too difficult. Jerzy Karczmarczuk PS. People who want always have one nice mathematical formula for some spherical problems too often forget that it is not necessary to have two singularities at the poles, just one is possible with the stereographic projection. But the distortions are awful... ** 
From: Kadir Haldenbilen <khaldenbilen@ya...>  20120417 17:45:56

You may try something like a Geodesic Dome. http://en.wikipedia.org/wiki/Geodesic_dome Kadir ________________________________ From: Joe Heafner <heafnerj@...> To: Visualpythonusers Visualpythonusers <visualpythonusers@...> Sent: Tuesday, April 17, 2012 8:12 PM Subject: [Visualpythonusers] covering a sphere with patches Can someone direct me to an algorithm for covering a sphere with patches of equal area for the purposes of illustrating the surface integral in Gauss's law? I've tried three so far and can't get good results. The problem is mostly with the poles and in the foreshortening of the patches near the poles. Is there a standard algorithm for this somewhere? Rectangular surfaces are easy. Joe Heafner Sent from one of my Macs  Better than sec? Nothing is better than sec when it comes to monitoring Big Data applications. Try Boundary onesecond resolution app monitoring today. Free. http://p.sf.net/sfu/Boundarydev2dev _______________________________________________ Visualpythonusers mailing list Visualpythonusers@... https://lists.sourceforge.net/lists/listinfo/visualpythonusers 
From: Joe Heafner <heafnerj@gm...>  20120417 17:12:40

Can someone direct me to an algorithm for covering a sphere with patches of equal area for the purposes of illustrating the surface integral in Gauss's law? I've tried three so far and can't get good results. The problem is mostly with the poles and in the foreshortening of the patches near the poles. Is there a standard algorithm for this somewhere? Rectangular surfaces are easy. Joe Heafner Sent from one of my Macs 
From: Bruce Sherwood <Bruce_S<herwood@nc...>  20120417 15:11:51

Ralph Martin kindly pointed out that I made a mistake in posting the new Mac installer for Python 3.2 (it required that Python 3.1 was installed instead of Python 3.2). Now fixed. I would appreciate a report from someone using the latest Mac operating system (Lion), as I built this on Snow Leopard. I don't expect any problem, because this was also the situation for VPython 5.72, which worked on Lion, but it would be good to know. Thanks. Bruce Sherwood 
From: Bruce Sherwood <Bruce_S<herwood@nc...>  20120417 14:32:42

>From what you describe, perhaps a curve object would suit your purposes better than an extrusion object. Bruce Sherwood 
From: Kadir Haldenbilen <khaldenbilen@ya...>  20120417 07:19:48

From: Bruce Sherwood <Bruce_S<herwood@nc...>  20120417 02:24:01

I'm afraid this is a feature, not a bug. There just isn't any way that I can think of for such a sharp turn to work in something called an "extrusion". Think about creating such an object by extruding metal and you may see that this is a fundamental problem. In the example program "extrusion_overview.py", step through the first page to get an index, then choose page 12 to see an illustration of the problem. On the other hand, perhaps you or someone else can come up with some scheme that would work better. Bruce Sherwood On Mon, Apr 16, 2012 at 8:12 PM, sufyan fehe <sisaala_20@...> wrote: > I am using the extrusion object library, path library of Vpyhon for my > project. my program simply extracts or parses Gcodes with X,Y, Z > coordinates, the program then uses this extracted points as my path, a 2D > square shape is then extruded through these points or path in that sequence. > the problem is, these points are line segments, where a line segment is > define by two points i.e X1,Y1,Z1 and X2,Y2,Z2. Now if the third point > X3,Y3Z3 is sharp turn, i.e the angle between the line segment becomes > 270, > the extrusion generates very long spikes or glitches which makes my work > messy. my Gcodes are all accurate, because it is tested. this is a special > case where the preceding point makes that sharp turn. i showed it to some > programmers and they say it might be a bug with vpython extrusion library. i > can share my program with you, or pictures of what i mean. hope i get a > response from you. thanks > 1 Attached file 6KB 
From: Eric Zárate <zarzzchile@gm...>  20120417 02:21:50

Can you share the part of the code in which is made the extrusion? and if is possible, upload an image and post the link. I had a similar problem before, but for don´t talk on the air, is better to see the example and try to find the specific solution. Eric. El 16/04/2012 22:12, sufyan fehe escribió: > > > >  > ** > > I am using the extrusion object library, path library of Vpyhon for my > project. my program simply extracts or parses Gcodes with X,Y, Z > coordinates, the program then uses this extracted points as my path, a > 2D square shape is then extruded through these points or path in that > sequence. > the problem is, these points are line segments, where a line segment > is define by two points i.e X1,Y1,Z1 and X2,Y2,Z2. Now if the third > point X3,Y3Z3 is sharp turn, i.e the angle between the line segment > becomes > 270, the extrusion generates very long spikes or glitches > which makes my work messy. my Gcodes are all accurate, because it is > tested. this is a special case where the preceding point makes that > sharp turn. i showed it to some programmers and they say it might be a > bug with vpython extrusion library. i can share my program with you, > or pictures of what i mean. hope i get a response from you. thanks > *1*Attached file *6*KB > > > > >  > Better than sec? Nothing is better than sec when it comes to > monitoring Big Data applications. Try Boundary onesecond > resolution app monitoring today. Free. > http://p.sf.net/sfu/Boundarydev2dev > > > _______________________________________________ > Visualpythonusers mailing list > Visualpythonusers@... > https://lists.sourceforge.net/lists/listinfo/visualpythonusers 
From: sufyan fehe <sisaala_20@ya...>  20120417 02:12:48

________________________________ I am using the extrusion object library, path library of Vpyhon for my project. my program simply extracts or parses Gcodes with X,Y, Z coordinates, the program then uses this extracted points as my path, a 2D square shape is then extruded through these points or path in that sequence. the problem is, these points are line segments, where a line segment is define by two points i.e X1,Y1,Z1 and X2,Y2,Z2. Now if the third point X3,Y3Z3 is sharp turn, i.e the angle between the line segment becomes > 270, the extrusion generates very long spikes or glitches which makes my work messy. my Gcodes are all accurate, because it is tested. this is a special case where the preceding point makes that sharp turn. i showed it to some programmers and they say it might be a bug with vpython extrusion library. i can share my program with you, or pictures of what i mean. hope i get a response from you. thanks 1Attached file 6KB 
From: sufyan fehe <sisaala_20@ya...>  20120417 02:11:04

I am using the extrusion object library, path library of Vpyhon for my project. my program simply extracts or parses Gcodes with X,Y, Z coordinates, the program then uses this extracted points as my path, a 2D square shape is then extruded through these points or path in that sequence. the problem is, these points are line segments, where a line segment is define by two points i.e X1,Y1,Z1 and X2,Y2,Z2. Now if the third point X3,Y3Z3 is sharp turn, i.e the angle between the line segment becomes > 270, the extrusion generates very long spikes or glitches which makes my work messy. my Gcodes are all accurate, because it is tested. this is a special case where the preceding point makes that sharp turn. i showed it to some programmers and they say it might be a bug with vpython extrusion library. i can share my program with you, or pictures of what i mean. hope i get a response from you. thanks 1Attached file 6KB 