[OSRS-PROJ] gauss-krueger/transverse mercator
Gerald I. Evenden
gevenden at capecod.net
Tue Jun 13 09:45:53 EDT 2000
What is interesting here is that PROJ.4 has a units conversion facility.
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).
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.
The confusing issue here is that there are now two "proj" programs.
Jerry Evenden and the Low Riders, Katie and Daisy May
gevenden at capecod.net http://www.capecod.net/~gevenden
----- Original Message -----
From: Morten Hulden <morten at ngb.se>
To: Markus Neteler <neteler at geog.uni-hannover.de>
Cc: <osrs-proj at remotesensing.org>
Sent: Tuesday, June 13, 2000 5:06 AM
Subject: Re: [OSRS-PROJ] gauss-krueger/transverse mercator
> Dear Markus
> +unfact= is a GRASS variable 'unit factor' that gets passed to proj's info
> structure as info->meters. It is also present in GRASS' internal
> location description file PROJ_UNIT.
> +unfact is the conversion factor from meters to other units
> (e.g. feet). The value of +unfact is 1 if the location unit is meters.
> get_proj.c is the routine that parses the pseudo-command line passed from
> GRASS and converts +unfact to a real PROJ parameter.
> +unfact is not the only GRASS specific parameter that will not be sent to
> PROJ as such; e.g. all spheroid names are parsed and converted to their
> 'a' and 'e2' values, which are then sent to PROJ routines. Spheroid names
> are never sent to PROJ. In fact, PROJ has a slightly different list of
> names for the spheroids, and does not know of some spheroids used in
> GRASS (e.g. 'sphere').
> hope this explains it
> why things were done as they were I have no idea
> but they work
> best regards
> Morten Hulden
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