[GRASS5] Even More on Projections

[Andreas Lange]

Hi Frank, hi Grassprogrammers,

Frank Warmerdam wrote:
> Andreas,
> 
> It hasn't been my experience that G_get_projinfo() returns defaults if
> PROJ_INFO is missing.  Are you sure that it does?  I had proposed changing
> G_get_projinfo() to generate defaults from the proj/zone settig in the
> WIND file if there was no PROJ_INFO file, but I didn't get any feedback
> (positive or negative) on this suggestion.

you are of cause right here. It was just wishful thinking on my side.
The call to G_get_projinfo() echoes that the file PROJ_INFO was not
found. But contrary the call to G_get_ellipsoid_parameters gives default
values (and the new functions for the datum support too).
G_database_projection_name() gets a name for the projection even if the
PROJ_INFO file is missing (from the WIND/DEFAULT_WIND file?). 
I think that this all needs some work to be consistent. This should be
discussed again when grass 5.0 is released.

> 
> As part of r.in.gdal I have implemented a projection comparison function
> (though it isn't really complete) which currently just lives in with r.in.gdal,
> but if folks think it is worthwhile, I would be happy to move it into libgis.a.
> 
> static int
> G_compare_projections( struct Key_Value *proj_info1,
>                        struct Key_Value *proj_units1,
>                        struct Key_Value *proj_info2,
>                        struct Key_Value *proj_units2 )
> 
> It returns TRUE if they appear to be the same, otherwise FALSE.
> 

Yes, i would vote for including in the gis library. 
I think that we should discuss how we can manage projection and datum
conversion in one step (different from my approach with the coordinate
conversion library), so that the {v|s|r}.proj commands can use a single
function call for conversion (with proj4). 
But all this requires some user input if datum conversion is really
needed. 

Thanks for your patience,

cu,

Andreas

-- 
Andreas Lange, 65187 Wiesbaden, Germany, Tel. +49 611 807850
Andreas.Lange at Rhein-Main.de - A.C.Lange at GMX.net



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