[OSRS-PROJ] Alternate Angular Units

Frank Warmerdam warmerdam at pobox.com
Sun Dec 1 19:19:36 EST 2002


I am hard at work upgrading OGR and libgeotiff to the EPSG 6.2.2
database, and as part of the effort I am reviewing all sorts of
outstanding issues related to the EPSG database, or PROJ.4's epsg

One issue that arises is that some EPSG coordinate systems, such as
those based on the "Nord Sahara 1959 (Paris)" datum use gradians as
the angular units.  Note that 200 gradians = 180 degrees.  The question
that arises is whether it makes sense for PROJ.4 to know anything about
alternate angular units for input/output of lat/long values.

If this is incorporated it would allow a more accurate representation of
a few exotic EPSG coordinate systems.   If done, I assume we would add
something like +to_degree=... listing a factor to apply to angular input
values to translate them to degrees before processing, and to apply
(inversely) after processing to return them to the original units.  I
would also suggest this value be processed by pj_transform() but not by
pj_fwd() and pj_inv().

The pj_fwd() and pj_inv() entry points already operate in radians (not
degrees), so they could be assumed to be operating at a level at which
this sort of issue is ignored, much like the suggestion of the prime
meridian applying to pj_transform(), but not pj_fwd() and pj_inv().

Any thoughts on the issue?

Best regards,

I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | Geospatial Programmer for Rent

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