<HTML dir=ltr><HEAD><TITLE>[Proj] Re: Global Gauss-Kruger and libproj4---the final story</TITLE>
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<DIV dir=ltr><FONT face="Times New Roman" color=#000000 size=2>WOW!</FONT></DIV>
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<DIV dir=ltr><FONT size=2>And some people call me arrogant ...</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Lighten up, fella.</FONT></DIV>
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<DIV dir=ltr><FONT size=2>Cliff Mugnier</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> Thu 28-Aug-08 19:04<BR><B>To:</B> strebe@aol.com<BR><B>Cc:</B> proj@lists.maptools.org<BR><B>Subject:</B> [Proj] Re: Global Gauss-Kruger and libproj4---the final story<BR></FONT><BR></DIV>
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<P><FONT size=2>On Thursday 28 August 2008 5:30:30 pm strebe@aol.com wrote:<BR>> >The only context that I use the term "interruption" in discussing<BR>> >cartographic projections are in cases like Goode's world maps or<BR>> >"orange peal" charts often using the sinusoidal projection. Please<BR>> >define what *you* mean by interruptions.<BR>><BR>> An interruption is any location where two points of infinitesimal<BR>> separation on the globe are mapped to two points having finite separation<BR>> on the plane. This happens somewhere on all projections. All along an<BR>> interruption, the projection formulæ are no longer a function; they are<BR>> multivalue.<BR><BR>Let's see. tan(x) has two values at x=90 degrees: +inf and -inf. So it is no<BR>longer a function, eh?<BR><BR>I can't find any such distinction for the definition of a "function." Please<BR>give reference.<BR><BR>Even if your questionable definition were true, it merely verifies that<BR>proj_fwd() is a function because it only returns one value. It is defined<BR>that way in the documentation.<BR><BR>In terms of interruptions applying to all projections I presume you are<BR>referring to the del-lon=180 condition. In many projection software this is<BR>not a break and the map merely repeats on in the x direction. As far as I am<BR>aware it is always the graphic programmers job to handle this condition and<BR>not the projection routine: when at the map edge recall the function with the<BR>sign of the lon term reversed.<BR><BR>BTW: you are the first person I have ever heard that refers to the wrap-around<BR>condition of longitude as an interruption if, indeed, that is what you are<BR>referring to.<BR><BR>If there are other examples, other than projections commonly recognized as<BR>interrupted (for example Goode) *please* name them.<BR><BR>> Regards,<BR>> -- daan Strebe<BR><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>_______________________________________________<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>