Maris, Many thanks for your detailed reply. My LIDAR files are not in LAS format - they are a mixture of ASC and TIF.
I spent a long time learning how to use QGIS and don't want to have to repeat the process with GRASS unless I have to. If there isn't a simple way to get r.contour to work from within the later versions of QGIS, then I'll keep on using the old version as the solution requiring the least effort. >From your comments, it would seem that it is how QGIS imports the LIDAR data which has changed and this is why I see the problem I reported. I also realise that QGIS is a global application whereas my work is restricted to the UK using the Ordnance Survey grid so I can't expect a huge resource to look at a narrow application. Cheers, Dave On Mon, 15 Feb 2021 at 10:08, Maris Nartiss <[email protected]> wrote: > 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 >
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