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Some points meant to be treetops are plotted beneath terrain surface, creating depressions in DTM

I realise that point cloud classification of “high vegetation” works best with GSD’s of less than about 8cm/pixel. I do appreciate its efficacy.

Yet, I think I’m not the only user who is plagued by “pits” or depressions in the DTM where trees have been removed. I believe the cause of these pits is that in some cases, some parts of tree canopies are plotted below ground level and are automatically assigned to “ground”.

This is a big ask: Can the point cloud classifier be trained to reject tree canopy points that end up lower than the immediate surrounding terrain? In woodland projects it is tedious to do this manually.

Images to illustrate my problem:
1 mosaic

5 dtm and contours

Hi @Wynand_Uys,

You might try using Pix4Dsurvey to help clean up here, though it won’t solve all your problems. One thing that is different in Pix4Dsurvey is that we don’t try to classify all classes, only terrain/non-terrain. In your case, the below ground trees would still be considered ground at first, but you could run the filter once, remove problems spots like those (should be quite visible), then run the filter again. From there you can make a terrain and export to LandXML, but I see you are using contours - Pix4Dsurvey can’t make those yet.

If you do try it, I’ll be curious to hear how it goes.

Pix4Dsurvey Product Manager