[Qgis-developer] QGIS CRS handling question

[Bo Victor Thomsen]

Otto -

The first question -

I you look at the information from "ogrinfo" in the first case it contains:

... DATUM["unknown", SPHEROID["unretrievable - using 
WGS84",6378137,298.257223563], ...

This is plainly wrong for EPSG:25833. It should be something with GRS80. 
You might have a bad installation of the GDAL utilities. And this error 
is probably triggering QGIS to ask for the projection.

For the next question: I haven't actually looked at the QGIS code for 
CRS lookups, but I'll make a guess:
QGIS do a search in the build-in projection database and find the 
epgs:3006 as the first candidate and doesn't look any further. You might 
have a look on this thread: 
http://lists.osgeo.org/pipermail/qgis-user/2013-February/021233.html , 
which describes a somewhat similar situation

Regards
Bo Victor Thomsen
AestasGIS
Denmark

On 22-05-2015 09:42, Otto Dassau wrote:
> Hi,
>
> I would like to understand QGIS behavior a little better for CRS handling.
>
> I have a tif/tfw file (input.tif) and would like to create compressed geotiff
> tiles from it (output.tif).
>
> 1) When I use
>
> gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES \
>   -a_srs EPSG:25833 input.tif output.tif
>
> gdalinfo shows:
>
> Driver: GTiff/GeoTIFF
> Files: output.tif
> Size is 16100, 15300
> Coordinate System is:
> LOCAL_CS["ETRS89 / UTM zone 33N",
>      GEOGCS["ETRS89",
>          DATUM["unknown",
>              SPHEROID["unretrievable - using WGS84",6378137,298.257223563],
>              TOWGS84[0,0,0,0,0,0,0]],
>          PRIMEM["Greenwich",0],
>          UNIT["degree",0.0174532925199433]],
>      AUTHORITY["EPSG","25833"],
>      UNIT["metre",1]]
> [...]
>
> loading this file in QGIS I am asked to provide the CRS for the layer,
> although it should be written in the GeoTiff header.
>
> 2) When I use
>
> gdal_translate -co COMPRESS=JPEG -co PHOTOMETRIC=YCBCR -co TILED=YES \
>   -a_srs "+proj=utm +zone=33 +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +units=m \
>   +no_defs" input.tif output.tif
>
> gdalinfo shows:
>
> Driver: GTiff/GeoTIFF
> Files: output.tif
> Size is 16100, 15300
> Coordinate System is:
> PROJCS["UTM Zone 33, Northern Hemisphere",
>      GEOGCS["GRS 1980(IUGG, 1980)",
>          DATUM["unknown",
>              SPHEROID["GRS80",6378137,298.257222101],
>              TOWGS84[0,0,0,0,0,0,0]],
>          PRIMEM["Greenwich",0],
>          UNIT["degree",0.0174532925199433]],
>      PROJECTION["Transverse_Mercator"],
>      PARAMETER["latitude_of_origin",0],
>      PARAMETER["central_meridian",15],
>      PARAMETER["scale_factor",0.9996],
>      PARAMETER["false_easting",500000],
>      PARAMETER["false_northing",0],
>      UNIT["metre",1,
>          AUTHORITY["EPSG","9001"]]]
>
>
> loading this file in QGIS, I am *not* asked to provide the CRS for the
> layer, but QGIS assigns the wrong CRS. In my case I want EPSG 25833 but get
> EPSG 3006 (which has the same parameters as 25833, but is not what I want).
>
> How can I make QGIS read the CRS correctly? Does anybody has a solution for
> this?
>
> Thanks a lot
> Otto
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