point density

[Karin...@ldbv.bayern.de]

Hello,

 

we use lasgrid to process density plots of our flight lines.

Was there a major change in coloring the density in LAStools version 20170818?

 

I send you a screenshot, showing a density plot with version 20170818 and a density plot from the version before.

 

the process is as follows:

 

lasgrid -i %OUTPUT_FILES%\flugstreifen_oduplicates\*.%RAW_FORMAT% -merged ^

       -density_32bit -step 5 -false -set_min_max 0 100 ^

       -cores %NUM_CORES% ^

       -mem 2000 ^

       -o %OUTPUT_FILES%\quality\density_4_pts.png

 

 

Regards,

Karin

 

[Martin Isenburg]

Hello,

For several years the '-density' option was printing out a WARNING that it's meaning would change to actual mean "density" rather than being the simple (and poorly named) point per grid cell counter that it was in its initial release. This point per grid cell counter is now called '-counter' and exists in differently more or less memory efficient versions.

-counter_32bit

-counter_16bit

-counter_8bit (or just -counter)

-counter_4bit

-counter_2bit

So if you want to continue to do the area normalization of the counter by the grid cell area yourself use:

lasgrid -i flugstreifen\*.laz -merged ^

     -counter_32bit -step 5 ^

     -false -set_min_max 0 100 ^

     -cores 4 ^

     -mem 2000 ^

     -o quality\density_4_pts.png

But look ... you clamp any counter bigger than 100 to red. So there is no point in using counters that can count up to 2^32-1 or 4,294,967,295. You can use the default 8 bit counter and your process will use 4 times less memory:

lasgrid -i flugstreifen\*.laz -merged ^

     -counter -step 5 ^

     -false -set_min_max 0 100 ^

     -cores 4 ^

     -mem 2000 ^

     -o quality\density_4_pts.png

Or you can use the new density option and directly set the min max to range from 0 to 4 points per square meter.

lasgrid -i flugstreifen\*.laz -merged ^

     -density -step 5 ^

     -false -set_min_max 0 4 ^

     -cores 4 ^

     -mem 2000 ^

     -o quality\density_4_pts.png

Note that for LAS or LAZ files that contain multiple returns per shot you will usually want to add '-keep_last' to get the (usually more meaningful) pulse density rather than the vegetation and other multi-return affected all point density.

Regards,

Martin @rapidlasso

PS: Warning ... version 20170818 had a bug in the LAS 1.4 compression.

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