Canopy Height Model - Remove Buildings

[Mark Tukman]

Hi All:

I'm trying to create a simple canopy height model using the code below.  The problem is, for some reason at least some buildings are still showing up as tall objects.  I am wondering the best way to zero out buildings in the chm.  For example, ts there a way to have lasheight automatically assign 0s to points classified as buildings (with replace_z).

Here is my code:

lastile -i *.laz ^

-tile_size 250 -buffer 20 ^

-extra_pass ^

-o tiled\b75.laz ^

-v

lasheight -i tiled\b75*.laz ^

-class 2 -replace_z -drop_below 0.0 ^

-odir height -olaz ^

-v -cores 6

lasthin -i %BLOCK%\classified\*.laz ^

        -subcircle 0.1 ^

        -step %SUBGRIDSTEP% -highest ^

        -odir %BLOCK%\tmp_dir -olaz ^

        -cores %CORES%

las2dem -i %BLOCK%\tmp_dir\*.laz ^

        -step %STEP% ^

-elevation ^

-set_min_max %MIN_MAX% ^

        -use_tile_bb ^

        -odir %BLOCK%\tiles_chm  -obil ^

        -cores %CORES%

[Terje Mathisen]

I also need to remove all buildings, this is in order to use the remaining non-ground points to develop a good vertical model of vegetation densities in order to determine runnability, which is sorted in multiple ranges on an orienteering map.

The approach I'm currently using starts with lasheight, ignoring classes 7,9,10&11, storing the new data as a layer:
lasheight -cores %CORES% -i adaptive\*.laz -ilay -ignore_class 7 9 10 11 -olay

Next I use lasclassify to determine the buildings, adding one more layer:
lasclassify -cores %CORES% -i adaptive\*.laz -ilay -ignore_class 7 9 10 11 -planar 0.1 -olay

Finally I run lasheight once more, this time ignoring any buildings and writing the output to "tiles_classified":
lasheight -cores %CORES% -i adaptive\*.laz -ilay -ignore_class 6 9 10 11 -drop_class 7\
 -drop_below -5 -drop_above 100 -classify_between 0.3 1.3 3 -classify_between 1.3 3.5 4\
 -classify_between 3.5 100 5 -odir tiles_classified -olaz

If the source laz files don't have usable ground classifications then I'll precede the steps above with a call to lasground_new:
lasground_new -cores %CORES% -i adaptive\*.laz -ignore_class 6 7 9 10 11 -fine -town -non_ground_unchanged -spike 3.0 -olay

In this stage I use -town instead of -wilderness in order for the lasground algorithm to not identify all larger buildings as vegetation!

Terje

Mark Tukman wrote:

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-- 
- <Terje.M...@tmsw.no>
"almost all programming can be viewed as an exercise in caching"

[George S. Mercier]

I'd probably just drop the building points all together rather than redefining there elevation data.

-George

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