[GRASS-user] Problem with Lidar Tools

[kaipi]

Thanks for your help ! Unfortunately I still don't get satisfying results
with the Lidar tools. Here is what I have done so far: 

- Updated to 6.4 on Windows: v.outlier doesn't work (see my post in Win
Grass forum)
- Installed Grass 6.4 RC 5 on Ubuntu (Ubuntu package): same results like on
Windows Grass 6.3
- Decreased spline steps to 0.04: v.outlier and v.lidar.edgedetection give
errors. My results are better the higher the spline steps are (> 20).
Brovelli recommends spline step 3 up to 4 times of the planimetric
resolution. AFAIK planimetric resolution means points per m². If I have 50
pts/m² this would mean a spline step of 200 ?? With spline steps about 20 I
get nice edges and with spline step of 400 complete buildings are detected
as edges. 
- Tried the Lidar demo data (nc_spm_08_2008_may18) and followed the
instructions on the Micro-tutorial_for_LIDAR_data_analysis:
v.lidar.edgedetection took so long, that I canceled process after 1 h (input
file has only 2000-3000 points - so something must be wrong)

I have also a problem to understand the definitions of first and last return
data. Here is a part of my Lidar data (ASCII format converted from raw LIdar
binary):

0 lon lat height intensity last first
1 3360422.27 5825275.62   37.16 255 1 1
2 3360421.94 5825275.60   38.21  56 0 1
3 3360422.48 5825275.60   37.18 255 1 0
4 3360422.17 5825275.58   38.18 141 0 1
5 3360422.65 5825275.58   37.26 255 1 0
6 3360422.84 5825275.56   37.31 255 1 1
7 3360423.05 5825275.54   37.32 255 1 1
8 3360423.36 5825275.52   37.13 255 1 1
9 3360423.06 5825275.50   38.11  12 0 1
10 3360423.60 5825275.50   37.09 255 1 0
11 3360423.70 5825275.49   37.32 255 1 1

First and last returns can be true (1) or false (0) or both. My
understanding is, that all points that have first return=true are first
returns and all returns that have last=true are last returns. When first and
last are true we have a single pulse otherwise we have double pulses.
If I understand the microtutorial correctly I need for v.lidar.growing as
input the last return single pulses (last=true and first=false) and as first
all pulses with first=true. 
But I get better results when I use as input all last return pulses (only
last=true) and as input only the first single pulses (first=true and
last=false).

I still have the problem that v.lidar.growing does not change categories.
Output has only 2 categories - same as output of v.lidar.edgedetection. 

I have attached two screenshots of my results so far (using the parameters
in my first post). I have not yet run v.surf.bspline.

http://n2.nabble.com/file/n3928180/lidar_before_after.jpg 

Classification after v.lidar.edgedetection:
http://n2.nabble.com/file/n3928180/edgedetected.jpg 

Any ideas regarding v.lidar.growing ? 

Thanks - Kaipi

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