[GRASS-user] r.contour

[Maris Nartiss]

Hello Dave,
r.contour should be working just fine. Your posted Warning is
harmless. Please try to run it in a pure GRASS session and not through
QGIS – in case of failure, it will be possible to get a reasonable
error message.

As for upgrading of GRASS – be ware – LiDAR tools depend on libLAS
that has been deprecated and is not shipped in most of recent Linux
distributions. Thus working with LAS files might be impossible at all.
There are planned new LiDAR tools based on PDAL in GRASS 8.

Māris.


2021-02-11 23:38 GMT+02:00, Dave Marshall <43carnaby at gmail.com>:
> Hello,
>
> I do a lot of work with UK LIDAR data and one of the most frequently used,
> and useful, GRASS routines for my work is r.contour. I am currently using
> GRASS through QGIS 3.4.12 and the associated version of GRASS is 7.6.1. I
> have made a couple of attempts to upgrade my QGIS version to a more recent
> one but this always results in a different version of GRASS which does not
> allow r.contour to work with the LIDAR files.
>
> QGIS 3.4 opens LIDAR tif files directly using EPSG:27700 as the CRS. Later
> versions of QGIS seem to require, or at least suggest, a transformation to
> an alternative CRS. Whether I use one of these transformations or not, the
> initial error I receive when running r.contour is "WARNING: Datum
> <Unknown_based_on_Airy_1830_ellipsoid> not recognised by GRASS and no
> parameters found". Other errors follow and finally there is a message to
> say that the routine has failed. I think that all the versions of GRASS
> which have generated this error are 7.8.
>
> I would like to upgrade my version of QGIS to a later version but am stuck
> with 3.4 because of my need for a functioning r.contour. QGIS contains a
> similar contour-drawing option but it does not allow the specification of
> upper and lower height limits and so can take a very long time to run on
> large files.
>
> Any help or advice will be much appreciated,
>
> Dave Marshall
>