Generating DEM only within a provided polygon

[André Kunert]

Hello, 

I have to calculate the DEM of countless small buildings. I have the footprints of the buildings as a polygon shape file. Is it possible to specify these footprints as boundaries for the "house-DOM"? Or do I first have to calculate a DOM for the whole area and then clip out the house areas again? Unfortunately I couldn't find anything in the readme file about this. For me, the areas outside the houses are not interesting, so that I don't want to calculate a DOM outside these house areas. I already tried it with -keep_class 6 -nodata -9999, but unfortunately it calculates the spaces in between anyway. Is there an hidden command?

Thanks a lot for your support.

[Martin Isenburg]

Hello André,

if you clip the LiDAR points with a shape file such that only the building footprints remain you can create a DSM of only the buildings if you set the '-concavity 1.0' value of las2dem to something that is lower than the spacing between the buildings (but higher than the pulse spacing). However, this DSM will not have very nice edges along the buildings as the typical boundary artifacts will occur. It might lead to better results to create a spike-free DSM

https://rapidlasso.com/2016/02/03/generating-spike-free-digital-surface-models-from-lidar/

that nicely preserves the building points and then clip the raster afterwards against your building footprint polygons.

Regards,

Martin

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