[GRASS-dev] Projection-problem

[Paul Kelly]

Hello Stephan

On Wed, 10 May 2006, Stephan Holl wrote:

> Hello Paul,
>
> thanks for replying! I really appreaciate your comments (and
> sollutions).

Apologies for not really keeping up with the list at all recently; this 
message just happened to catch my eye!

>> Hello Stephan
>> What is GK Zone 4 (DHDN)?
>
> This is similar to EPSG:31468, from Oracle Spatial Datasets.

OK sorry I was confused asking that---that field isn't used for 
determining the projection; it is just meant to be human readable AFAIK 
and it wasn't the problem.

>> It seems that the GDAL function
>> OSRExportToProj4() is returning a PROJ.4 string with a missing
>> "proj=" parameter, because it can't convert "GK Zone 4 (DHDN)" into a
>> projection.
>
> OK, thanks for clarifying this. But apparently ogrinfo returns at least
> correct projections parameters like
> PRIMEM["Greenwich",0.000000], UNIT["Decimal
> Degree",0.01745329251994330]], PROJECTION["Transverse Mercator"],
>    PARAMETER["Scale_Factor",1.000000],
>    PARAMETER["Central_Meridian",12.000000],
>    PARAMETER["False_Easting",4500000.000000],
>    UNIT["Meter",1.000000000000],
>
> Could that be a problem with the different strings from Oracle here?

Yes. I think the problem is the missing underscore _ between Transverse 
and Mercator. Seems simple but confuses the OGR function and I'm really 
not sure how best to handle it.

>> GRASS is crashing because it assumes that there will
>> always be a proj= value, not unreasonable I don't think! I could
>> change it so it won't segfault but I think it would be better if the
>> OSRExportToProj4() function returned an error code when it can't
>> determine the projection.
>
> Yes, the latter would be the better choice afaik. Non-segfaults are
> always appreciated :-) Would this be a big task and is it worth to
> have such a short-term solution?

OK I've changed it now to print a warning if the projection name is 
missing rather than giving a segfault (however the resulting projection 
parameters will not be much use!).

Best regards

Paul