[GRASS-user] Error using g.region and visualizing LAS files

Hamish hamish_b at yahoo.com
Sun Feb 5 20:47:10 EST 2012

Patrick wrote:
> I am a first time GRASS user working on a project through the
> Department of Transportation.  We're trying to visualize LiDAR
> data we have collected from a particular segment of roadway so
> that we can better analyze and present our finding to the DoT,
> and I have been encountering some issues following the tutorial
> found here.
> When using the Serpent Mound data available from this site as
> well as my own data, I start encountering problems while
> attempting to use the g.region command.  It says that n= *max x*
> etc is an invalid input.  I think this is because the g.region
> is stuck on LAT/LON units for this, however trying to use the
> LAT/LON from my own data has not worked either, and I do not
> know how to access the LAT/LON data for the Serpent Mound set.
> How do I make the program accept my g.region inputs?
> I tried to move on with the other commands despite g.region not
> working, and encountered more issues.  When I inputted the
> r.in.xyz (....) command it said "Reading data...." but when I
> tried r.colors it said "ERROR: Bad y-coordinate line 1 column 2"
> My ultimate goal for right now is to replicate these results
> with my own data.  After that we would like to experiment 
> further with the advanced capabilities of the program, but a
> colored visualization of the data would be great for right now.

ok, so the first thing you need to know is the coordinate system
and format of your LIDAR data. For the Serpent Mound dataset
the projection info is: UTM zone 17, using the WGS84 datum.
So you'd need to run the Location Wizard at grass startup and
create a Location using those parameters. GRASS makes you work
in one primary coordinate system at a time.

Is your data natively in lat/lon or some local projection system?
If it is in lat/lon and your purpose is 3D visualization, it is
highly recommended to reproject it into a meter-based coord
system like UTM. then x, y, and z coordinate data are all in
the same space system and the 3D stuff is much smoother.
It's pretty simple to do that by chaining a 'm.proj -i' command
into the r.in.xyz step.

The file format for the Serpent data is LAS. Is yours in LAS
or is it a plain text file (.csv or similar)?

what do the first 10 lines of your data file look like?

what do your g.region and r.in.xyz command line options look like?
(exact cut and paste is best, including error messages)

it's all very smooth and straight forward once you figure out
the recipe, so keep trying, you'll get there..


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