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<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri>Mikael,</FONT></P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri></FONT> </P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri>Here's another way of looking at the problem.
<SPAN style="mso-spacerun: yes"> </SPAN>Our Web Mercator discussion a few
years ago turned out to be about a (new, though some have commented that it was
around before Google) non-conformal map projection (Web Mercator) and NOT about
the differences between an ellipsoidal and a spherical earth. <SPAN
style="mso-spacerun: yes"> </SPAN>Your situation may be the
same.</FONT></P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri></FONT> </P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri>You say your data are stored in
stereographic, but stereographic using spherical or ellipsoidal equations? <SPAN
style="mso-spacerun: yes"> </SPAN>Do you know?<SPAN
style="mso-spacerun: yes"> </SPAN>Probably spherical (and I'd guess
there's no difference between Snyder and Double Stereographic for the sphere)
because if ellipsoidal then you'd have to be using an eccentricity and your
reference surface would be an ellipsoid (probably WGS84) and not the NinJo
sphere. <SPAN style="mso-spacerun: yes"> </SPAN></FONT></P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri></FONT> </P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri>If so, then we have just defined the Web
Stereographic map projection, spherical stereographic equations applied to
ellipsoidal WGS84 coordinates, probably non-conformal. <SPAN
style="mso-spacerun: yes"> </SPAN>You can work out the distortions (scale
and convergence) and you're done.<SPAN style="mso-spacerun: yes">
</SPAN></FONT></P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri></FONT> </P>
<P style="MARGIN-TOP: 0in; MARGIN-LEFT: 0in; MARGIN-RIGHT: 0in"
class=MsoNormal><FONT face=Calibri>Noel</FONT></P>
<DIV> </DIV>
<DIV style="FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: 12pt">Noel Zinn,
Principal, Hydrometronics LLC<BR>+1-832-539-1472 (office), +1-281-221-0051
(cell)<BR>noel.zinn@hydrometronics.com (email)<BR>http://www.hydrometronics.com
(website)<BR></DIV>
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<DIV style="FONT: 10pt tahoma">
<DIV> </DIV>
<DIV style="BACKGROUND: #f5f5f5">
<DIV style="font-color: black"><B>From:</B> <A title=Mikael.Rittri@carmenta.com
href="mailto:Mikael.Rittri@carmenta.com">Mikael Rittri</A> </DIV>
<DIV><B>Sent:</B> Tuesday, March 06, 2012 7:38 AM</DIV>
<DIV><B>To:</B> <A title=proj@lists.maptools.org
href="mailto:proj@lists.maptools.org">proj@lists.maptools.org</A> </DIV>
<DIV><B>Subject:</B> [Proj] Trouble georeferencing data stored in a spherical
projection.</DIV></DIV></DIV>
<DIV> </DIV></DIV>
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style="FONT-STYLE: normal; DISPLAY: inline; FONT-FAMILY: 'Calibri'; COLOR: #000000; FONT-SIZE: small; FONT-WEIGHT: normal; TEXT-DECORATION: none">
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<P class=MsoSalutation><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Hello, (I hope this is
approximately the right forum).<o:p></o:p></SPAN></FONT></P>
<P class=MsoNormal><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>I have had some trouble
with meteorological GeoTIFF data, stored in stereographic<BR>based on a GEOGCS
called “NinJo sphere”, without any EPSG code, using a sphere<BR>with radius
6378137 m.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>The main problem wasn’t
the lack of an ordinary geodetic datum, since the most detailed<BR>file had the
resolution 4.6 km, much more than the typical difference between datums.
<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>What bothers me more,
with spherical data, is that it seems impossible to know if the<BR>spherical
latitude should be interpreted as identical to WGS84 latitude (geodetic
latitude),<BR>or if it should be interpreted as geocentric latitude that needs
conversion to WGS84.<BR>The difference between the two interpretations can be up
to 21 km, which can be<BR>significant even when the datum choice isn’t.
<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>I was hoping to find that
one of the alternatives was a de facto standard, but<BR>instead I found evidence
that both of them are in use.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Spherical latitude =
geodetic latitude is used by:<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US> Data in Web Mercator, like Open Street
Map,<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US> Meteorological data in any of the
models WRF, MM5 and NinJo.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Spherical latitude =
geocentric latitude is used by:<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US> MISR Regional UAE2 Imagery (from NASA
Earth Data).<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>In an old post, Melita
Kennedy has written that it is “probably more correct” to use the<BR>second
convention; maybe she has experience with data like MISR.
<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>The Proj.4 FAQ discusses
Web Mercator and mentions “many other datasets … such as<BR>many NASA datasets”
as using the same convention, so maybe NASA is not consistent<BR>in its choice
of convention. <o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Anyway, what I would like
is some standard way to tag the metadata, in GeoTIFF in<BR>my case but more
generally in WKT, to specify which convention is used. <BR>Of course, the
problem is already solved in Proj.4, as the FAQ says, since we can
use<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>
+nadgrids=@null<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>for the first convention,
and<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>
+towgs84=0,0,0<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>for the second
one.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>In GeoTiff, specifying
TOWGS84[0,0,0] in the same way will be possible as soon<BR>as the proposal <A
href="http://trac.osgeo.org/geotiff/wiki/TOWGS84GeoKey">http://trac.osgeo.org/geotiff/wiki/TOWGS84GeoKey</A>
is supported,<BR>but there will still be no way to specify the first
convention.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>In WKT, too, only the
second convention can be specified.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>So I wonder, is there
already some discussion going on about how the first convention<BR>could be
specified? (Perhaps within OGC or EPSG.) If not, can we start it?
<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Best
regards<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Mikael
Rittri<BR>Carmenta<BR><st1:country-region w:st="on"><st1:place
w:st="on">Sweden</st1:place></st1:country-region><BR><A
href="http://www.carmenta.com/">http://www.carmenta.com</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"
lang=EN-US>REFERENCES:<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>The way to interpret WRF
and MM5 data: <A
href="http://www.ie.unc.edu/cempd/projects/mims/spatial/grids_ellipsoids_map_proj.html">http://www.ie.unc.edu/cempd/projects/mims/spatial/grids_ellipsoids_map_proj.html</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>The way to interpret
NinJo data: personal trial-and-error.<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>The way to interpret MISR
UAE2 data: <A
href="http://eosweb.larc.nasa.gov/PRODOCS/misr/uae/imagery/regional/map_projection.html">http://eosweb.larc.nasa.gov/PRODOCS/misr/uae/imagery/regional/map_projection.html</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt" lang=EN-US>Melita Kennedy’s post: <A
href="http://lists.osgeo.org/pipermail/metacrs/2008-August/000144.html">http://lists.osgeo.org/pipermail/metacrs/2008-August/000144.html</A><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt">Proj.4 FAQ: </SPAN></FONT><FONT
face=Arial><SPAN style="FONT-FAMILY: arial" lang=EN-US><A
href="http://trac.osgeo.org/proj/wiki/FAQ#ChangingEllipsoidWhycantIconvertfromWGS84toGoogleEarthVirtualGlobeMercator"><SPAN
lang=SV>http://trac.osgeo.org/proj/wiki/FAQ#ChangingEllipsoidWhycantIconvertfromWGS84toGoogleEarthVirtualGlobeMercator</SPAN></A></SPAN></FONT><FONT
face=Arial><SPAN style="FONT-FAMILY: arial"><o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt">
<o:p></o:p></SPAN></FONT></P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"><o:p></o:p></SPAN></FONT> </P>
<P class=MsoBodyText><FONT size=3 face=Arial><SPAN
style="FONT-FAMILY: arial; FONT-SIZE: 12pt"><o:p></o:p></SPAN></FONT> </P></DIV>
<P>
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