[GRASS-user] r.contour

[Dave Marshall]

Maris,

Thanks for the advice. Note that I am running QGIS in Windows, not Linux. I
managed to open GRASS 7.8.5 directly, load a LIDAR file and run r.contour
but I'm not at all familiar with running the programme this way. The LIDAR
didn't load with the correct CRS and although r.contour seemed to run
properly according to the command output, no lines appeared on the image as
they do in QGIS. I suspect that I need some of the functionality in QGIS
than I can't get from GRASS alone so this may not be a way forward for me.

Dave

On Fri, 12 Feb 2021 at 05:25, Maris Nartiss <maris.gis at gmail.com> wrote:

> 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
> >
>
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