#169 [changed] Clip plot elements to arbitrary convex shape

[Michael Hecht]

I have a problem with contours which might be
corrected in coming releases.

Since pm3d can interpolate non grid data it might
be possible to learn this to contour. The result would
be a figure like the attached one (which I produced by
hand)

[Michael Hecht]

[Petr Mikulik]

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No, pm3d does not interpolate data.

You probably want something else -- that's already in current gnuplot.
I guess it maybe this FAQ:
3.14 How to overlay contour plot over pm3d map/surface
(contours can be or coloured by "with palette").

[Michael Hecht]

[Michael Hecht]

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Sorry, but this doesn't work (i.e. I tried to do so).
I always get:

Notice: cannot contour non grid data!

So I need to get contours on non grid data which is currently not possible.
I attached the data to plot which is comparable to the former attached jpeg.
Maybe it helps to understand the problem.

I plotted it using mainly:

set pm3d map interpolate 10,10 ftriangles flush center
set view map
splot "nongrid.dat"

P.S.: pm3d does interpolate data, since the command is: "set pm3d interpolate 10,10"
P.P.S.: The FAQ might help at my request ID 1655289, even if it is no comfortable solution.
The only problem I have there is the (unnecessary) connection between contour,
surface and data
style

File Added: nongrid.dat

[Petr Mikulik]

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You must use "set dgrid3d ..." to grid your data for contouring.

[Michael Hecht]

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I tried this, but the result was not what I wanted to get (see the jpeg file I attached at the beginning).
I don't want a rectangular figure (which I get with "dgrid3d").
If it is this easy you can surely reproduce (basically) the "contour.jpg" with
a few lines of gnuplot commands?!
(If you can I definitely have to send you a little donation)

[Petr Mikulik]

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As I understand it now, you want to see your data only inside the shape of your experimental data? Huh, that's exactly the reason I wrote pm3d long long time ago :-))

I don't know how to do such a masking. Preprocess your input data, from limiting scans get a curve and from it make a shape "towards infinity" and then fill it in white colour... Ugly indeed.

Or code a function for the contour alg "set the z-value of points outside of the input data shape to NaN".

Someone else has a better idea?

[Michael Hecht]

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This is the resason, why I wroter a program what transforms the data like this.

1. Get data with a grid like structure, but not in a rectangular shape,
i.e. missing values, but if values available then in a grid
(this is what you usually get when you make SELECT X,Y,avg(Z) ... GROUP BY X,Y ...
from a database, you will never get all combinations of all classes)
2. enhance the data by extrapolation towards x- and y-range
3. Calculate the convex hull of the original data
4. restrict extrapolated data to the convex hull
5. plot it with gnuplot :-)

I attached an image where you can see the difference between the plot of the original data (not the ones I attached before) and the convex hull inter-/extrapolation.

still missing

6. add contours to the non rectangular shape

All this could really be a powerful enhancement of pm3d!!
Like:
set pm3d enhance # to inter and extrapolate to a grid, but dufferent than dgrid3d
set pm3d convex # display all within convex hull (see wikipedia: graham hull)

File Added: convexhull.jpg

[Michael Hecht]

[Nobody/Anonymous]

[Petr Mikulik]

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In summary: This feature request asks for "Draw contours inside a (an explicitly) given area.".

[Ethan Merritt]

Now supported in version 5.5
See the mask_pm3d demo
and documentation on the new support for calculation of convex hulls.