[GRASSLIST:2217] Re: Projection questions

[Eric G. Miller]

On Mon, Jul 30, 2001 at 08:20:36AM +0000, Michel Wurtz wrote:
> Glynn Clements wrote:
> > 
> > Rich Shepard wrote:
> > 
> > >   I know that '99' is used for both 'user specified' and 'spc', but I cannot
> > > find a list of codes for other projections.
> > 
> > The following is from gis.h:
> > 
> > #define PROJECTION_XY  0
> > #define PROJECTION_UTM 1
> > #define PROJECTION_SP  2
> > #define PROJECTION_LL  3
> > #define PROJECTION_OTHER  99
> > 
> 
> Well, this show how old (and linked to its initial use) is this part
> of Grass Code.  I think this is an area where all major commercial GIS
> are now much more better (proj. info for each layer and proj. conversion
> "on the fly", large choice for projection, including user defined, etc).
> Maybe another part of Grass to rethink ?

Yes.  We've discussed doing so for GRASS 5.1. Maybe, something like:

  *  Geographic (Geodetic) Coordinate System
     +  Datum
  *  Projected Coordinate System
     +  Predefined Coordinate System
        -  State Plane
	   o  Datum
	     =  State
	       ~  County
	-  Universal Transverse Mercator
	   o  Datum
	     =  Zone
	       ~  Hemisphere
	-  Universal Polar Stereographic
	   o  Datum
	     =  Hemisphere
	-  (others...)
     +  User Defined Coordinate System
        -  Albers Conical Equal Area
	   o  Datum
	     =  Parameters
	-  Lambert Conformal Conic
	   o  Datum
	     =  Parameters
	-  Transverse Mercator
	   o  Datum
	     =  Parameters
	-  (others...)
  *  Unreferenced (Cartesian) Coordinate System
        -  Units

The management of coordinate systems should've been reorganized when
the proj4 library was added.  Instead, we got this PROJECTION_OTHER
thing.  Anyway, all the infrastructure is present, it's just the
organization of it that needs help.

-- 
Eric G. Miller <egm2 at jps.net>