<HTML dir=ltr><HEAD><TITLE>Re: [Proj] lat/long to northing/easting and back again</TITLE>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>I'd like to point out that NADCON and its derivatives do exactly that - the algorithm does a bi-linear interpolation in terms of the graticule. The ultimate "accuracy" is dependant on the fineness of the "mesh" of the graticule, and not on the interpolation.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>C. Mugnier</FONT></DIV>
<DIV dir=ltr><FONT size=2>LSU</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Christopher Barker<BR><B>Sent:</B> Mon 16-Mar-09 11:28<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] lat/long to northing/easting and back again<BR></FONT><BR></DIV>
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<P><FONT size=2>Roger Oberholtzer wrote:<BR>>> First, interpolating positions from easting/northing values is shaky and<BR>>> accuracy of such efforts is highly dependent upon the distance between points<BR>>> used in the operation.<BR><BR>My first thought is -- why so this in projected space? It sounds like<BR>you have lat-long, and you want to interpolate between two points, and<BR>get back lat/long again. So could you do this in lat-long space?<BR><BR>To answer that, we need to know what you mean by interpolate?<BR><BR>Do you have two points and want to know what the midpoint is, for<BR>example? If so, what does "mid point" mean? That's not obvious on a<BR>globe, which may be why you're using projected coordinates, but with<BR>Gerald's recently released geodetic (geodesic?) tools, it should be<BR>doable to find a point along a great circle connecting two points, for<BR>instance.<BR><BR>> The distance is in the order of meters. Typically less than 10.<BR><BR>In that case, you can probably get pretty darn close by pretending that<BR>that lat-long units are Cartesian -- and that would be really easy! How<BR>accurate do you really need to be?<BR><BR>-Chris<BR><BR><BR>--<BR>Christopher Barker, Ph.D.<BR>Oceanographer<BR><BR>Emergency Response Division<BR>NOAA/NOS/OR&R (206) 526-6959 voice<BR>7600 Sand Point Way NE (206) 526-6329 fax<BR>Seattle, WA 98115 (206) 526-6317 main reception<BR><BR>Chris.Barker@noaa.gov<BR>_______________________________________________<BR>Proj mailing list<BR>Proj@lists.maptools.org<BR><A href="http://lists.maptools.org/mailman/listinfo/proj">http://lists.maptools.org/mailman/listinfo/proj</A><BR></FONT></P></DIV></BODY></HTML>