las2dem

[Sara Shirowzhan]

Hi Martin,

I have a lidar data with over 51 million points and when I use las2dem to make a raster of elevation, I receive the errors in the attached file.

Could you please advise what should I do?

Kind Regards,

Sara

[Martin Isenburg]

Hello Sara,

from the WARNING that says:

WARNING: only 18 bytes until point block when trying to read 72 bytes into header.vlrs[0].data

I get the feeling your LAS / LAZ file has a corrupt header. Can you provide a complete lasinfo report? 

http://rapidlasso.com/lasinfo

Your file simply has too many points for las2dem. You have 3 options.

(1) use a tile-based workflow with each tile having fewer than 20 million points

http://rapidlasso.com/2015/08/07/use-buffers-when-processing-lidar-in-tiles/

(2) use the BLAST extension of LAStools (simply run blast2dem instead of las2dem)

http://rapidlasso.com/blast2dem

(3) use the new 64 bit executable of las2dem simply by adding '-cpu64' to the command line. However, only BIL, ASC, DTM, XYZ, and LAZ are currently supported. But you need to download the latest version (180911) of LAStools for this

http://rapidlasso.com/LAStools

Regards,

Martin @rapidlasso

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[Mikael Sejersen]

Hi Martin, 

If option 1 (tile-based workflow) is used, is there a way to merge the tilled tiff dsm's back together to one dem.tif reflecting the source las? 

/Mikael 

[Martin Isenburg]

Hello,

Yes. If you produce BIL, LAZ, ASC, XYZ, or DTM elevation raster with las2dem with the '-use_tile_bb' option (assuming they were tiled with buffers using lastile) then you can use lasgrid to merge them into a single output raster. It's important to set the '-step 0.5' to whatever the tiled rasters were created with because by default lasgrid will produce rasters of step size 1. Note that TIF does not scale beyong a certain size. Use IMG instead. For BIL, ASC, XYZ, or DTM you also need to respecify the CRS with '-epsg 12345' or so.

http://rapidlasso.com/lasgrid
http://lastools.org/download/lasgrid_README.txt

lasgrid -i tiles_dtm\*.bil ^

            -merged ^

            -step 0.5 ^
            -epsg 12345 ^

            -o single_dem.tif

lasgrid -i tiles_dtm\*.asc ^

            -merged ^

            -step 0.5 ^

            -epsg 12345 ^

            -o single_dem.img

lasgrid -i tiles_dtm\*.laz ^

            -merged ^

            -step 0.5 ^

            -o single_dem.bil

But for raster operations most folks would usually use GDAL which is a raster processing package. Here is GDAL merge.

https://www.gdal.org/gdal_merge.html

Regards,

Martin @rapidlasso