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ContourBuilderForTin doesn't like coordinates of zero

See original GitHub issue

When a ContourBuilderForTin is initialised with a vertices list where some vertices have 0 in either the x or y coordinate, the following error is returned. Fudging the coordinates by 0.0001 fixes the problem.

java.lang.NullPointerException: Cannot invoke "org.tinfour.contour.PerimeterLink.addContourTip(org.tinfour.contour.Contour, boolean)" because "pStart" is null
	at org.tinfour.contour.ContourBuilderForTin.buildRegionsUsingPerimeter(ContourBuilderForTin.java:701)
	at org.tinfour.contour.ContourBuilderForTin.buildRegions(ContourBuilderForTin.java:638)
	at org.tinfour.contour.ContourBuilderForTin.<init>(ContourBuilderForTin.java:253)

Issue Analytics

State:
Created 3 years ago
Comments:10 (10 by maintainers)

Top GitHub Comments

1reaction

gwlucastrigcommented, Apr 21, 2021

I basically have this fix completed and have posted an updated version of the code in the repository. I am still doing some final clean up, adding some more comments and Javadoc, etc. I will be submitting the final version soon.

The issue was related to the many special cases that can occur when contours are allowed to pass through vertices… That is, when there exist vertices with the exact z values as a contour. I did quite a bit of rework on the code to address these situations. I’ve also added an inspection utility that performs several tests to verify that a result is correct.

The attached an image was created by contouring elevation data from a Lidar sample taken over Bear Mountain in Salisbury Connecticut. The image represents a 1 kilometer square area. Contours are drawn at 5 meter intervals ranging from 540 meters to 705 meters above mean sea level. ContourLas05

1reaction

gwlucastrigcommented, Mar 24, 2021

I just posted improvements to contouring to address this issue. However, I’ve discovered some new special-cases that cause the contouring to fail. So I am leaving this issue open and continuing work.