[Proj] "Double Ellipsoid" error, reproduction

[Frank Warmerdam]

Gerald I. Evenden wrote:
> I think more desirable approach is to create a d2d program with optional i/o 
> filtering through projection procedures.  One might have options like:
> 
> d2d --in=EPSG1234 --out=NAD83_1105
> 
> where --in and --out may refer to library systems but one can also have
> 
> d2d --in=proj=latlon --datum_in=xyx --datum_out=mm \
>           --out="proj=merc ellps=WGS84 R_A"

Gerald,

Modulo syntax differences, cs2cs can already be used just to do the datum
transformation step if desired.  So I don't see your point.

> To me, that kills all mice with flexibility and ease of use.  *AND* you can 
> easily use libproj4 updates.  ;-)

I would note that this still does nothing for the folks who use PROJ.4
within another program like MapServer or GDAL.  There typically the
application knows very little about the coordinate systems or what steps might
be used.  They just call pj_init() for the source and destination coordinate
system and then call pj_transform().

This is *by far* the most common use of PROJ.4 and then there is no
option to setup program pipelines.

Best regards,
-- 
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I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
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and watch the world go round - Rush    | Geospatial Programmer for Rent