[GRASS-user] r.contour

[Dave Marshall]

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
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