mapgen - map.def problems

[Gerald I. Evenden]

>Date: Wed, 15 Jun 94 09:13:08 CDT
>From: jschuler at ncg.scs.ag.gov (Jill Schuler)
>Sender: grass-lists-owner at max.cecer.army.mil
>Reply-To: grassu-list at max.cecer.army.mil
>To: ekoster at let.rug.nl, grassu-list at max.cecer.army.mil
>Subject: Re: mapgen - map.def problems
	... much deleted
>
>Second problem:  I think you compiled the wrong proj code.  Any way here's 
>the fix.  Under src.related/mapgen/proj/src there is a file called
>pj_ellps.c .  This file stores all the ellipsoid names known to the proj
>command.  Unfortunately CERL uses different ellipsoid names then Jerry even
>though they based there projection libs from MAPGEN.  TO FIX THE PROBLEM
>YOU MUST ENTER ALL THE GRASS ELLIPSOID NAMES IN THIS FILE AND RECOMPILE THE
>PROJ COMMAND.  I WILL ATTACH THE EDITED FILE I MODIFIED FOR YOU TO USE.
>
>The attached file was copied with the /tmp path, so be sure to move it back to
>src.related/mapgen/proj?/src before compiling.
>
>That should fix your problem.  Let me know.

That may fix his problem, but it gives me more gray hairs.

>Jill
	..., again much deleted

What follows are a few of the changes highlighted:

>"MERIT",	"a=6378137.0", "rf=298.257", "MERIT 1983",
>"GRS80",	"a=6378137.0", "rf=298.257222", "GRS 1980(IUGG, 1980)",
>"grs80",	"a=6378137.0", "rf=298.257222", "GRS 1980(IUGG, 1980)",

	why didn't MERIT get lower case treatment?

>"airy",		"a=6377563.396", "b=6356256.910", "Airy 1830",
>"mod_airy",	"a=6377340.189", "b=6356036.143", "Modified Airy",

	based on later "modif" changes, why not the above?

>"aust_ntl",	"a=6378160.0", "rf=298.25", "Australian Natl, S. Amer., IAU 64",
>"australian",	"a=6378160.0", "rf=298.25", "Australian Natl, S. Amer., IAU 64",

	The previous job must have been selecting identifier names for X11

>"GRS67",	"a=6378160.0", "rf=247.247167", "GRS 67(IUGG 1967)",
>"bessel",	"a=6377397.155", "rf=299.1528128", "Bessel 1841",
>"bess_nam",	"a=6377483.865", "rf=299.1528128", "Bessel 1841 (Namibia)",
>"clrk66",	"a=6378206.4", "b=6356583.8", "Clarke 1866",
>"clark66",	"a=6378206.4", "b=6356583.8", "Clarke 1866",

	add "a", but why not correctly spell it: Clarke ?

>"clrk80",	"a=6378249.145", "rf=293.4663", "Clarke 1880 mod.",
>"clark80",	"a=6378249.145", "rf=293.4663", "Clarke 1880 mod.",

	ibid

>"everest",	"a=6377276.3452", "b=6356075.4133", "Everest 1830",

	I had to change the above a few releases ago to the following:

evrst30 a=6377276.345    rf=300.8017      Everest 1830
evrst48 a=6377304.063    rf=300.8017      Everest 1948
evrst56 a=6377301.243    rf=300.8017      Everest 1956
evrst69 a=6377295.664    rf=300.8017      Everest 1969
evrstSS a=6377298.556    rf=300.8017      Everest (Sabah & Sarawak)

	etc., etc.

Obviously there is no law saying one can't alias the ellipsoid names
to any name one wants to select, but it sorely taxes the modularity of the
overall system, makes maintenance a headache and drives people *up
a wall* when they try (because of their MAPGEN-PROJ knowledge) to help a user.

As an fellow programmer once said: "It's not that I didn't know,
I never suspected."

Gerald (Jerry) I. Evenden   Internet: gie at charon.er.usgs.gov
voice: (508)563-6766          Postal: P.O. Box 1027
  fax: (508)457-2310                  N.Falmouth, MA 02556-1027