[Qgis-user] No transform available between XXX and EPSG:4326 when using non-Earth projections

[Even Rouault]

Sebastian,

I can reproduce the 2 error messages you got. There's indeed something 
in QGIS that tries a terrestrial reprojection and should be fixed, but I 
don't think this is really critical apart of the annoyance of being 
spammed about that. Please file a QGIS issue to track this. That said, I 
managed to do a non-Earth reprojection by adding a custom CRS with the 
following WKT definition:

GEOGCRS["MARS Geographic",

DATUM["D_MARS",

ELLIPSOID["MARS",3396000,0,

LENGTHUNIT["metre",1,

ID["EPSG",9001]]]],

PRIMEM["Reference meridian",0,

ANGLEUNIT["degree",0.0174532925199433,

ID["EPSG",9122]]],

CS[ellipsoidal,2],

AXIS["longitude",east,

ORDER[1],

ANGLEUNIT["degree",0.0174532925199433,

ID["EPSG",9122]]],

AXIS["latitude",north,

ORDER[2],

ANGLEUNIT["degree",0.0174532925199433,

ID["EPSG",9122]]]]

and selecting it as the project CRS. Using ESRI:104905 (GCS_Mars_2000) 
seems to also work (I haven't deeply checked but I do get a reprojected 
raster and geographic coordinates), but you'll get each time the 
warnings about the 2 terrestrial coordinate operations. Hopefully in 
coming months, I'll be able to ingest the IAU catalog into the PROJ 
database as well.

Even

Le 18/03/2021 à 21:07, Sebastian Walter a écrit :
>
> Hi,
>
> Since Version 3.X I'm not able to perform transformations on planetary 
> (non-Earth) data (from e.g. Mars or Mercury, example dataset: 
> https://maps.planet.fu-berlin.de/mex4/h1104_0000.ihs.53.tif). The 
> error message is:
>
> No transform is available between SINUSOIDAL MARS and Custom CRS: 
> GEOGCRS["unknown",DATUM["unknown",ELLIPSOID["WGS 8….
> proj_create_operations: Source and target ellipsoid do not belong to 
> the same celestial body
> No transform available between SINUSOIDAL MARS and EPSG:4326
>
> The consequence is that transformations to lat/lon are not possible 
> any more. With the older QGis there was no problem like this. My 
> suspect is the "new" Proj6 database layout, but the above error 
> messages also point to the fact there there is some EPSG:4326 
> projection hard-coded into Qgis.
>
> Is anybody successfully using Qgis with non-Earth data and proper 
> transformations?
>
> Thanks for any advise...
>
> Sebastian
>
>
>
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