[GRASS5] problems with [rsv].proj

[Frank Warmerdam]

Eric G. Miller wrote:
> On Thu, May 30, 2002 at 05:39:58AM +0100, Glynn Clements wrote:
> 
> 
>>In the longer term, we should re-think the architecture of the PROJ
>>library. There are many practical applications where it would be
>>useful to have more information about the overall "nature" of a
>>projection than just a pair of functions which project individual
>>points.
> 
> 
> While not supporting all the nifty cartographic projections like proj4,
> the Geotrans projection routines from NIMA will signal an error if the
> coordinate is outside the reasonable limits of the projection.  The code
> for this library is pretty well thought out, but it is limited to about
> 15 of the most common projections (though that covers most needs) and
> some things like the projection used in F-16 fighter jets could be done
> without ;-).  To support grid shift type datum transformations would
> require hacking into the datum code.  One nice thing, is it includes
> geoid (EGM96) vertical corrections for wgs84 ellipsoid vs. mean sea
> level.  Another thing some might find nice is the various projection
> error values and significant digit rounding it provides (based on some
> scale factor).

Eric / Glynn,

I would be happy to incorporate some sort of support for error estimation
support in PROJ.4 if practical.  However, in general returning regions in
which a projection is valid is very difficult.

I would also note that PROJ.4 *does* contain datum shifting based on grids,
(like US nadcon grids, and Canadian NTv1 grids) as well as 3 and 7 parameter
datum shift approximations.  The 3/7 parameter support was derived from
Geotrans.  Hopefully this can be properly incorporated into GRASS in 5.1. I
was a bit weirded out that datum shifting was grafted into GRASS late in the
pre-release countdown sequence.

I would be interested in including some sort of geoid conversion support in
PROJ.4 but I have very little experience with it, and am I am not clear on
the need for it.  Hopefully others with the need can help drive such work.

Best regards,

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