HELP!! Clark66->WGS84 ???#%@*!

[Phil Chaney]

> 
> Date sent:  24-AUG-1992 12:09:56 
> 
> Hello grassusers:
> 	I was wondering if someone would be kind enough to explain the method
> I should take to transform a lat-lon site dataset which is referenced to
> clark66 spheroid into a UTM location so that it will be correctly located with
> respect to new lat-lon data referenced to the WGS84 spheroid and also converted
> to UTM. I want to do this so that the historic data will be correctly
> referenced to new data collected with GPS.
> 
> 	I've read through the GRASS Reference Manual and can't get a good
> enough handle on this to be sure I'm going about it the correct way. I also
> don't understand the dx,dy,dz parameters in the m.datum.shift program. Any
> help would be GREATLY APPRECIATED!
> 
> Thanks for your time.
> 
> Gerry Hatcher                   
> 
> Ocean Mapping Development Center|      gerry at omdc.gso.uri.edu {Internet}
> University of Rhode Island      |            cbeam::gerry {span}
> voice (401)-792-6940            |            fax (401)-792-6849
> 
> 
Hi Gerry,

1.  What kind of data do you have (points, lines, or areas) in clark66
    that you want to convert? 

2.  For this kind of conversion, (one datum to another based on different
    spheroids) m.ll2u will not help because it does not do datum conversions,
    it just makes the transformation from spherical geometry coordinates
    (lat-lon) to plane surface coordinates (utm), based on what spheroid
    the lat-lon positions were based on!

3.  Clark66 "spheroid" is a "best fit" description of North America in 1866.
    WGS 84 is an "earth centered" description (ellipsoid) of the entire
    planet based on satellite observations.

I hope this info will help. If I find a command in grass that will help,
I will let you know. I know that NGS has a program called CORPSCON
that does NAD27 conversion to NAD83, which was designed to be compatible
with WGS84. This is a pc program, but I understand that this program may 
be in the process of being converted into grass code for a later release.

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Phillip L. Chaney       Center for Advanced Spatial Technologies
Research Specialist     National Center for Resource Innovations-SW
                        12 Ozark Hall 
       N                University of Arkansas
       |                Fayetteville, Arkansas 72701             
    W -+- E             Phone: (501) 575-6159                 
       |                       (501) 575-4575                  
       S                FAX:   (501) 575-3846                     
                        E-mail: phil at spock.uark.edu
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