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<DIV><FONT face=Arial size=2>I don't know the details of what's going on inside
proj, but I do see that if I take out the+towgs84 argument I get:</FONT></DIV>
<DIV><FONT face=Arial size=2>C:\Proj\bin>cs2cs +proj=latlong +datum=WGS84 +to
+proj=mill +ellps=clrk66 +lon_0=0 +units=m<BR>2.35
48.85<BR>261603.65 5916486.09
0.000</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>which is closer to your Oracle results. clrk66
doesn't seem like the right ellipsoid for WGS-84 but (a) I can never remember
how to get a list of ellipsoid codes from proj and (b) even a sphere would
probably do the job for a "world projection". And NAD27 is for North America - a
best fit as of 1927 knowledge. But your test point is in Europe. So I wouldn't
expect your +towgs84 values to be useful there.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I think you should keep in mind that if you're
talking about a world projection, you're talking about scales in the order of
1:100 million, where even a skinny 0.1mm line width will cover 10km on the
ground. The odd metre or two or thousand won't make much
difference.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<BLOCKQUOTE
style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=pmezard@gmail.com href="mailto:pmezard@gmail.com">Patrick Mézard</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=proj@lists.maptools.org
href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, January 12, 2006 7:07
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [Proj] MapInfo/Oracle
Cylindrical Miller Parameters</DIV>
<DIV><BR></DIV>Hello,<BR>In search of a good-looking world projection I came
across Miller Cylindrical one. Fortunately, both MapInfo and Oracle Spatial
know about it, and even better agree on transformations from WGS84 to Miller
for several points. This is important because it is always easier to debug
something when the input or output can be reproduced on other tools. Now I
would like to use it in proj.4 but as usual I am stuck trying to figure out
*the parameter string*.<BR><BR>I am taking the Oracle WKTEXT description as
reference:<BR>"""<BR>PROJCS["Miller Cylindrical", GEOGCS [ "NAD 27
(Continental US)", DATUM ["NAD 27 (Continental US)", SPHEROID ["Clarke 1866",
6378206.400000, 294.978698]], PRIMEM [ "Greenwich", 0.000000 ], UNIT
["Decimal Degree", 0.01745329251994330]], PROJECTION ["Miller Cylindrical"],
UNIT ["Meter", 1.000000000000]]<BR>"""<BR><BR>It converts (2.35, 48.85) into
(261360.667, 5916639.52).<BR><BR>NAD27 datum is defined by:<BR>"""<BR>NAME =
NAD 27 (Continental US)<BR>SHIFT_X = -8<BR>SHIFT_Y =
160<BR>SHIFT_Z = 176<BR>"""<BR><BR>Oracle WGS84 and Clarke 1866 ellipsoids
definitions are the same than proj.4 ones.<BR><BR>and finally tried something
like:<BR>"""<BR>cs2cs +proj=latlong +datum=WGS84 +to +proj=mill +ellps=clrk66
+towgs84=-8,160,176 +lon_0=0 +units=m<BR>2.35
48.85<BR>261360.67 5889006.49
-12281.453<BR>"""<BR><BR>So, cs2cs output x coordinate perfectly matches
Oracle's one, but the y differs by 27633m.<BR>I tried to replace the Clarke
ellipsoid with a sphere defined by the minor then the major axis but it does
not improve the result.<BR><BR>Just to be clear: I do know that configuring
Miller projection with a WGS84 datum would give me usable results. What I am
looking for is compatibility with existing applications, to ease debugging and
allow release to third parties without complicated explanations about why this
is not the same thing than the one they see in their GIS dialog boxes while
having almost the same name.<BR><BR>What do you think about this? Are these
discrepancies to be expected because of differences within projection
implementations? Did I miss something when configuring the
projection?<BR>Thank you for any idea.<BR><BR>--<BR>Patrick Mézard<BR><BR><BR>
<P>
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