v.digit and NAD

Malcolm Williamson malcolm at cast.uark.edu
Thu May 18 08:00:00 EDT 1995

Hi, Bob!
I'm definitely not the expert on this subject, but I know enough to say 
that this is not painless. First of all, v.digit is not going to do a 
thing for you. If you were interested in doing a simple projection 
change, from, say, State Plane to UTM, you would use v.proj, _as_long_as 
you_were_working_in_the_same_datum_!! Datum transformations are much more 
complicated; they are not based on simple mathematical models. The latest 
version of the program "proj", which is used by GRASS to do projection 
transfromations, includes a module called "nad2nad" which is specifically 
for converting between NAD27 and NAD83. The problem is that it is not 
seemlessly hitched to GRASS! Definitely a "roll you own" proposition. You 
will need to do a "v.out.ascii" to get ASCII coordinate pairs to use with 
the program. Perhaps someone else out there would like to describe their 
own experience, as I have never done this in GRASS... (I cheat and use 
other GIS packages :-) ).
        -Malcolm Williamson
         Center for Advanced Spatial Technologies
         University of Arkansas, Fayetteville AR

On Thu, 18 May 1995, Robert Atnip wrote:

> All the data in my system is based on NAD27.  I was wondering if I
> digitize a map based on NAD83, how hard would it be for v.digit to
> automatically convert the data to NAD27.  
> Bob Atnip
> Camp Atterbury

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