<HTML dir=ltr><HEAD><TITLE>Re: [Proj] Libproj4 manual opinion poll</TITLE>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>Normal Mercator can indeed have "2 standard parallels," but they are always symmetric about the Equator. I have done one that is legally recognized in Ecuador for the city of Guayaquil to cover a larger area of interest outside of the old city limits (for the greater Metro area), with minimal scale distortion. It is simply done by having a scale factor at origin less than 1.0 at the Equator.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Watch your blood pressure.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>C. Mugnier</FONT></DIV>
<DIV dir=ltr><FONT size=2>Louisiana State University</FONT></DIV></DIV>
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<FONT face=Tahoma size=2><B>From:</B> proj-bounces@lists.maptools.org on behalf of Gerald I. Evenden<BR><B>Sent:</B> Mon 29-Sep-08 10:35<BR><B>To:</B> PROJ.4 and general Projections Discussions<BR><B>Subject:</B> Re: [Proj] Libproj4 manual opinion poll<BR></FONT><BR></DIV>
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<P><FONT size=2>One thing quickly becomes apparent: the confusion as to what is the difference<BR>between proj.4 and libproj4.<BR><BR>In terms of cartographic projections, nearly nothing. In terms of datum<BR>shifts and other miscellany: everything. libproj4 as with the original<BR>proj.4 software had nothing to do with datum shifts other than the original<BR>distribution had a separate section that dealt only with the NAD datums. The<BR>original proj program also had a mechanism for generating Tchebyshev<BR>polynomials that were designed for use with the mapgen map graphic system.<BR><BR>For the end user, the difference between running proj and lproj is trivial and<BR>the user can use the original report for proj when using lproj without<BR>getting into trouble. There are a few more projections in libproj4 library<BR>and lproj than the old system.<BR><BR>There have been a few peculiarities introduced into the proj.4 material, some<BR>I can understand and some that I cannot (to put it very mildly).<BR><BR>1. Alternate longitude origins. Are not supported in libproj4 (nor original<BR>proj). Some usefulness and a valid suggestion for libproj4.<BR><BR>2. Alternate origins for some projections. I shudder when I see "two standard<BR>parallels" listed for plain ol' Mercator. There is not even one standard<BR>parallel, let alone two. There is a latitude of true scale and that only<BR>adjusts the k_0 factor so that the scale factor is 1. at the selected<BR>latitude. If one wants to shift the origin then use x_0, y_0. Stuff like<BR>that really raises blood pressure.<BR><BR>I am sure there are others but that is a starter list.<BR>--<BR>The whole religious complexion of the modern world is due<BR>to the absence from Jerusalem of a lunatic asylum.<BR>-- Havelock Ellis (1859-1939) British psychologist<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>