Canopy height model

[Ivan Kljun]

Hello,

 

I am trying to rasterize the canopy following this steps: https://rapidlasso.com/2014/11/04/rasterizing-perfect-canopy-height-models-from-lidar/ . First I use lasheight and then lasgrid, but the raster cell values I get are from 0-250. What am I doing wrong because I suppose I should get values of vegetation height from 0 to some 30 m?

 

Ivan

[JP]

Ivan,
It helps to copy the commands that you used into your post, so people can pick through what you did to find possible solutions. I am definitely no guru with this stuff, but I've been messing with it for a couple of months now. Are your LiDAR (.las?) files already categorized into ground, building, vegetation returns? Did you already create the canopy model? Based on your message, you started with lasheight. The link you gave said to start with lasground. Did you use lasground first? Did you use -replace_z in lasheight? These questions would be answered if you had copied and pasted your steps here. Without knowing what you did specifically, no one can answer your question.

[Ivan Kljun]

Yes, my LIDAR data (Slovenia) are already categorized into ground, vegetation(low, medium, hight),…

 

I also tried to use like this:

 

lasground -i drawno.laz ^

          -wilderness ^

          -o ground.laz

lasheight -i ground.laz ^

          -drop_above 30 ^

          -replace_z ^

          -o normalized.laz

lasgrid -i normalized.laz ^

        -step 0.33333 ^

        -highest ^

        -false -set_min_max 0 25 ^

        -ll 278200 602200 -ncols 300 -nrows 300 ^

        -o chm_grd.png

But the raster values are from 0-255, and the trees are maybe 30-40 m maximum?

Sorry for not pasting the steps from the beginning I realize I is much more clear this way.

Ivan

--
Download LAStools at
http://lastools.org
http://rapidlasso.com
Be social with LAStools at
http://facebook.com/LAStools
http://twitter.com/LAStools
http://linkedin.com/groups/LAStools-4408378
Manage your settings at
http://groups.google.com/group/lastools/subscribe

[Martin Isenburg]

Hello Ivan,

You are not creating a raster with actual values as output but one that maps the height to an RGB color ramp that goes from blue via yellow to red that is then stored to the PNG image format that is not suitable for storing height values. you are doing this via these options here:

   -false -set_min_max 0 25 ^

        -o chm_grd.png

See the documentation of lasgrid how to output the actual values (not a '-false' color) to some other raster format that can store height or elevation values such as ASC, BIL, TIF, IMG, ...

http://rapidlasso.com/lasgrid

http://lastools.org/download/lasgrid_README.txt

This one here should do the trick:

lasgrid -i normalized.laz ^

        -step 0.33333 ^

        -highest ^

        -o chm_grd.bil