Drape tool leaving gaps on terrain


The drape tool seems to be leaving gaps in the terrain whenever the drape line intersects with corners of triangles in the triangulated mesh. Turning on the hidden geometry after performing drape on the attached terrain using the lines as added in the model, you clearly see the pattern. It’s like : “all good - oh no, an intersection - better skip the next triangle - all good again!”

If you offset the lines a tad bit then everything works fine.

Hope you can find a fix to this. For landscape architects, the drape tool is an invaluable tool for adding texture and manipulating terrain, and a buggy drape function results in many accumulated hours over time manually fixing these gaps.

Here is the file :

Drape_test.skp (2.8 MB)


Until then, if you have, you can try to use Fredo Tools on Surface

I did some tests, and it seems this problem has always happened. Also found that the gaps when doing a drape exactly match gaps you get when doing an intersect. Which I think makes it be an intersect issue and not a drape one. I suspect intersect issues would end up higher on the list than drape issues.

I made this simpler model to use in a new bug report.

IntersectIssue2017.skp (400.4 KB)

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Hi Colin!

I checked out your smaller test model. Assuming the terrain on the right was a drape, i intersected your vertical plane with the terrain on the left and a found a couple of areas where the (assuming it was?) drape performed slightly better than the intersect :

Both were intersect. I wasn’t trying to prove that drape and intersect are identical, I had decided that when testing the original terrain and taking screenshots of the two techniques.

I did do some patching to make the example geometry have parallel edges instead of being jaggy. When they were jaggy looking that was a distraction, I didn’t want developers to think of the geometry as having problems because of how jaggy it looked. It is quite possible the two bits of geometry were not identical.

My plan was not to mention drape in the bug report at all. If this intersect variation gets fixed, and that doesn’t completely fix drape as well, then I’ll make a new bug report.

Got it, I see what you’re going for. Good luck sorting it all out!

I added this simpler model and testing steps:

  • Open SimpleIntersectExample2017.skp
  • Right-click on the rectangle group, and choose Intersect Faces/With Model.
  • Note that the new edges are created for the first four faces, but not the last one.