[OSRS-PROJ] gauss-krueger/transverse mercator

Andreas Lange Andreas.Lange at Rhein-Main.de
Wed Jun 14 18:25:37 EDT 2000

Dear Mr. Evenden,

just some comments on GRASS and PROJ.4:

Gerald I. Evenden wrote:
> A second comment is the ellipsoid naming.  PROJ has an easily maintainable
> table for ellipsoids.  Since there was freedom for the other mods, why
> wasn't updating the table done?  However, for some applications, I agree
> with the basic a=, e2=, etc. method.  Also, units conversion can also be
> achieved by merely controlling the units of a= (and b= and any other
> parameter like x_0, y_0).

GRASS has (for historical reasons?) its own ellipsoid table. This table
is a plain ascii file, so that it can be changed without the need for
recompiling. The values for a and e2 are read from the GRASS database
file, as the information for the ellipsoid is associated with the GRASS
location. I think the ellipsoid table inside GRASS was updated by Morten
Hulden when he updated the projection support in GRASS. So there was no
need to update the ellipsoids in PROJ.4. 
> As a final note, rather than changing PROJ.4 it seems easier to change the
> application software that uses the PROJ.4 library and leave the program
> unchanged and irrelevant to the project.  Program *proj* is more of an
> example of how to use the system and a useful filter but not a totally
> universal tool.  The library is the important *universal* tool.

GRASS uses PROJ.4 code unchanged. Only two functions are added
(pj_get_kv for reading parameters from the GRASS location database and
set the values with pj_init and pj_do_proj to do the actual projection
of a point). pj_do_proj is only a wrapper to use pj_fwd or pj_inv. So
the entry points of the library are used unchanged.  
> The confusing issue here is that there are now two "proj" programs.

Not with GRASS. What Markus Neteler described is the interactive version
m.proj of GRASS, which is only a user interface within GRASS.


Andreas Lange
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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