[GRASS-user] r.contour

[Maris Nartiss]

Hello Dave,
QGIS hides a bit of GRASS complexity by making a guess for various
parameters. As with any guess – sometimes it works, sometimes it is a
miss (and user has no idea which is the case).

To get contours out of LAS files:
1) create a location with coordinate system matching one used by LAS
files (be ware – you might need to know it in advance from metadata as
LAS files quite often lack this information);
2) create a mapset for the area of interest (could be whole region or
a single file in case of parallel processing);
3) start GRASS in newly created mapset;
4) set up your computational region (this is most important part!)
with g.region. Don't forget to choose appropriate resolution.
a) if you know the extent in advance (e.g. from a map sheet grid) use that;
b) if you don't know the extent in advance, use actual extent from the
LAS file. I would advocate to use r.in.lidar -s and set the extent
manually with g.region – you can “snap“ your raster to coordinates.
5) import data with r.in.lidar;
6) run r.contour on the map;
7) export with v.out.ogr to Shapefile (#teamshapefile).

Good luck,
Māris.

P.S. When you wander into area of 66000 LAS files occupying nice 14T
on your disk, only a few adjustments need to be done + a bit of Python
coding + a bit of cluster management :D