[GRASS-user] Re: Problem with Lidar Tools

[benmarillier]

Hi All, 

I am having similar problems to Kaipi in regards to the v.lidar.growing
stage of LiDAR processing. I'm running GRASS 6.4.0 on Windows. My dataset is
a 1km by 1km tile of LiDAR with a point spacing of about 1.5 points/m2, so a
total of about 1.5 million in the area of interest. 

Thus far I've imported the points with v.in.ascii, split into the first
returns and last returns. I interpreted these two classes as follows (please
correct me if I'm wrong)... 

First returns: all first returns, including single returns where only one
return has been received. 
Last returns: all single returns, and the last return where multiple returns
have been received. 

Then I removed outliers as per the micro-tutorial on the GRASS wiki. 

Next I ran v.lidar.edgedetection on the last returns with the default
parameters. 

This resulted in a reasonable looking classification of edge (2), not-edge
(1) and uncertain (3). The edges of the buildings and trees are quite well
defined, as shown in the image below, so far so good... 

...however, when I run v.lidar.growing (default parameters), the output I
get is exactly the same as the edgedetection output. The points are
classified identically into 1, 2 and 3, and there appears to have been no
change in the classification. I've tried varying the growing parameters, and
changing the region resolution, but the output is always the same.   

I've trawled through the forums to no avail, so any advice would be greatly
appreciated. 

Thanks, 
Ben 

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