<div dir="ltr">I've been following a few of the recent threads on this list regarding enhancements to Proj's datum transformations. Pretty exciting stuff! <div><br></div><div>One group of transformations that seems to have been ignored for a number of years is applying the HARN hpgn grids in the Proj epsg file. For example the Proj epsg entry for epsg:3758 uses +towgs84=0,0,0,0,0,0,0 but I believe that is should use +nadgrids=wyhpgn.gsb, or at least that's what I change it to, which produces results that match NADCON.<div><div><br></div><div>Is anyone aware of a reason that nadgrids are not referenced in the epsg file? Is it maybe just an oversight, something that nobody ever got around to? Or because distributing nadgrids would become burdensome?</div><div><br></div><div>It seems like pretty low hanging fruit. HARN has been around for about 20 years. The nadgrid files are already there. Differences between +towgs84=0,0,0,0,0,0,0 and +nadgrids=XXhpgn.gsb are on the order of a meter in the few places I have looked, so it's a fairly significant correction (or error, depending on your point of view). "grep -c HARN epsg" returned 264 and "grep -c 'hpgn' epsg" returned 0, so effects a lot of definitions.</div><div><br></div><div>Maybe I'm missing something. I'd be interested in any comments.</div><div><br></div><div>Rich</div><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr">Richard W. Greenwood, PLS<br><a href="http://www.greenwoodmap.com" target="_blank">www.greenwoodmap.com</a></div></div>
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