[OSRS-PROJ] gauss-krueger/transverse mercator

Morten Hulden morten at ngb.se
Tue Jun 13 05:06:16 EDT 2000

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

On Tue, 13 Jun 2000, Markus Neteler wrote:

> > The "+unfact" option *is not* of my doing and comes from some non-USGS
> > distribution.  I'm mystified and curious of its purpose.
> --------
> Morten, could you please teach me/us about "unfact" parameter?
> I shall store it somewhere in GRASS sources.
> > > > As for "unfact" I have absolutely *no* idea what that is.
> > > This I cannot recall, but was told it once when wondering about it.
> > > Sorry - no help today...
> > >
> > > Morten Hulden <morten at ngb.se>, who updated the m.proj of GRASS 5,
> > > explained it to me last year.

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