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<TITLE>reading georeferencing tables for GRASS</TITLE>
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<FONT FACE="Verdana, Helvetica, Arial"><SPAN STYLE='font-size:12.0px'>Paul and Glynn,<BR>
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I'm ready to move ahead and try to create PROJ.4 strings in the wxgrass location wizard, but am confused about the parameters tables in $GISBASE/etc.<BR>
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It looks kind of like proj-params.table and maybe proj-units.table are the files used by g.setproj and that the others (datum.table, datumtranform.table, ellipse.table, and projections) are there to help create a PROJ.4 string for GRASS. Is this correct?<BR>
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If this is the case, I'm not quite sure how to use these. <BR>
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The datumtransforms.table seems the most straightforward--just search for the line with a projection that matches the location projection and read of the datum transformation parameters ("towgs84=24,-130,-92") as a single PROJ.4 string to add on to the PROJ.4 string of the location projection.<BR>
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I do use projections? That is, choose the projection code that is appropriate for the description that I want.<BR>
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the datum.table and ellipse.table are more confusing. The datum table seems to include ellipsoids, but only a subset and does not include the ellipsoid parameters. I can look up the ellipsoid in the ellipse.table file that matches the ellipsoid in the datum.table file and grab the ellipsoid parameters. But what about all the ellipsoids that are not in the datum.table file? Can they be used? <BR>
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It seems that, hypothetically, you could use a different ellipsoid with a datum besides the one associated with it in the datum.table file. But I don't know why those particular ellipsoids are in the datum.table file. Are these simply the most common for that datum or do I *need* to use the ellipsoid associated with that datum?<BR>
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I hope that you can help me get it clear how these 2 tables are related so that I can begin to parse them into a PROJ.4 string.<BR>
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Thanks<BR>
Michael<BR>
__________________________________________<BR>
Michael Barton, Professor of Anthropology<BR>
Director of Graduate Studies<BR>
School of Human Evolution & Social Change <BR>
Center for Social Dynamics & Complexity<BR>
Arizona State University<BR>
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phone: 480-965-6213<BR>
fax: 480-965-7671<BR>
www: <a href="http://www.public.asu.edu/~cmbarton">http://www.public.asu.edu/~cmbarton</a> <BR>
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