shifting DLG data

[Phil Chaney]

> 
> 
> The 175 meter error is of the right magnitude to be caused
> by improper matching of UTM "spheriods".  The DLG data was
> likely produced referenced to the "clark66" (NAD27) spheroid,
> and your GPS may be using a more modern spheroid.
> You could use m.ll2u and m.u2ll to convert your GPS
> control points to the different datum.
> 
> Jim Hinthorne
> GIS Lab
> GIS Lab
> 
As I understand m.ll2u from info from Michael Shapiro, this program
only converts latlon to utm. If you need to perform a datum conversion,
CORPSCON from NGS will do that (as will many other commercial programs).
In a recent request for info on this question, Michael Shapiro indicated
that CORPSCON may be incorporated into v.proj in the future.

It appears as if you have used gps to collect registration points for
a map. You should be able to redefine the output format of the gps
data to match the DLG (probably NAD27, while gps correction software set
to output NAD83 or WGS 84).
........................................................................
Phillip L. Chaney                                  Center for Advanced
Research Specialist                *    *          Spatial Technologies
                               *            *         /\    /\    /\    
CAST/NCRI-SW                                       --------/--\--------   
University of Arkansas              ____            /    \/    \/    \  
Phone: (501) 575-4575                /\            National Center for 
E-mail: phil at spock.uark.edu         /  \           Resource Innovations     
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