LL coordinate system

[Gerald I. Evenden]

>Date: Tue, 27 Apr 1993 10:36:15 UTC+0200
>From: "(Usuario de GRASS 4)" <grass4 at tilo.datsi.fi.upm.es>
>Subject: LL coordinate system
>
>I want to convert a scanned map (x,y coordinate system) into latitud/longitude
> coordinate system. With the i.points (i.rectify,...) command I can convert 
>my map into the UTM coordinate system or the State Plane coordinate system 
>but not into latitud/longitude coordinate system.
>Does anyone know how I could do this?.
>Thanks in advance.
>
>Anabel Donadios
>Eurogis

Since there does not seem to be an answer from the GRASS gurus, I will
dare to jump in with a non-GRASS answer.

Yes, is is possible, but only if you are willing to do a little
programming.  I will also place a caviate caviate that you must, among
your x-y coordinates,  have points where you know either the lat/lon or
the cartesian system you want to convert to.  Using these points, you
can determine (in a least squares sense) bivariate polynomials which
will "correct" your values to the distination system.

An expanded explanation can be found in a PostScript file pub/OF91-17.ps.Z
on  charon.er.usgs.gov's (128.128.40.24) FTP/anon.

If you have further questions, please email me direct.

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