[GRASS-user] Warning regarding Datum unknown not recognised by GRASS

[Markus Neteler]

On Tue, Jun 29, 2010 at 11:20 AM, Kim Besson <kimbesson1981 at gmail.com> wrote:
> Greetings
> A couple of days ago I have exchanged a few messages with Paul Kelly and
> Micha Silver regarding this issue. But now I have a new example and I want
> to know if I'm doing anything wrong and better understand what is  GRASS
> behaviour.
> I'm trying to have an aumatic procedure to reproject images using gdalwarp.
> First it checks image CRS (g.proj input=IMAGE -jf) and compares with
> Location's CRS (g.proj -jf).
> As target_CRS I'm using the output from g.proj -j -f .
> In this case, g.proj -jf give me the Location«s CRS:
> +proj=utm +south +no_defs +zone=24 +a=6378137 +rf=298.257223563
> +towgs84=0.000,0.000,0.000 +to_meter=1
> (Sidenote. This Location was created based on an EPSG)
> I use this expression to warp the image:
> gdalwarp -t_srs "+proj=utm +south +no_defs +zone=24 +a=6378137
> +rf=298.257223563 +towgs84=0.000,0.000,0.000 +to_meter=1" input.tif
> proj4.tif
> But if I check proj4.tif CRS I get this:
> +proj=utm +south +no_defs +zone=24 +a=6378137 +rf=298.257223563 +to_meter=1
> Trying to open with OGR...
> Trying to open with GDAL...
> ...succeeded.
> Datum <unknown> not recognised by GRASS and no parameters found
> Why towgs84 is not kept in the image?

To my knowledge the GeoTIFF format is not able to keep the towgs84 string.
Did you try with different formats?

But in general, it may be better to assign proj metadata via EPSG code.

Markus