Contour level at arbitrary (x,y)

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Chad Greene 2013-6-11

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With a contour plot I can use the Data Cursor to click on an (x,y) point and get the Level at that point.

Can I get these Levels from the command line, given an arbitrary (x,y)? I know I can regrid or interpolate the zdata set, but I'd like to extract the values that are plotted, not interpolated values.

Thanks!

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Answer 1

Walter Roberson 2013-6-11

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Set distinct colors for each level. Display. Frame capture. Determine mapping between x/y coordinates and pixels. Now, for each (x,y) pair to be query, map into the captured frame, extract the color, and do a reverse lookup based on the color to determine which contour level corresponds to that color.

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Chad Greene 2013-6-12

Interesting idea, Walter. I'll have to think of an efficient way to implement your suggestion. My only concern is that the (x,y) points of pixels corresponding to any lines between patches, or any text, or any tick marks or legends would return an incorrect or undefined Level value.

The only other solution I could think of was to use inpolygon with the patch vertices. This seems to work for some patches, but not others. I haven't determined exactly why some patches are problem causers.

Walter Roberson 2013-6-12

The polygons generated by contouring are not clean polygons surrounding each contour level. Instead, each edge is drawn just once as part of some polygon. Mostly the uppermost (smallest) contour gets done as a single polygon, but mostly anything else ends out not being explicitly constructed.

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