Hello Dave, your case is even easier – TIFF and ASC both are raster formats and thus it is a simple task: import -> contour -> export (skipping all point cloud related tweaking).
Create a new location. Either select coordinate system directly or use one from TIFF file. Import data with r.in.gdal – don't forget to specify "-e" parameter – it will align the computational region with the imported raster. Then proceed to use r.contour followed by v.out.ogr. In future – do not ask for help with LiDAR but ask for help with raster data. Otherwise you'll get advices like you got from me – how to work with point clouds although you are looking for how to work with ordinary rasters. Māris. 2021-02-15 22:58 GMT+02:00, Dave Marshall <[email protected]>: > 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 >> > _______________________________________________ grass-user mailing list [email protected] https://lists.osgeo.org/mailman/listinfo/grass-user
