[Proj] proj4 definition for transverse mercator projection from RegCM3 model for North America

Hailey Eckstrand haileyeckstrand at gmail.com
Tue Jul 27 15:39:04 EST 2010

> >
> >Hello,
> >
> >> The sphere ellipsoid is a guess as they didn't provide the geographic
coordinate system
> >
> >check your parameters, especially if the assumption about the sphere is
correct and if the
> >sphere is of a right size? Test with the normal NAD83, NAD27, WGS84 datums
with their
> >correct ellipsoids Clarke 1866,  GRS 80 and WGS84 etx.
> >
> >http://en.wikipedia.org/wiki/North_American_Datum
> >
> >http://en.wikipedia.org/wiki/World_Geodetic_System
> >
> >Janne.
> I just looked through some of the RegCM3 source code. I did find a 6371229.0
value in the projection section
> of terrain.f. It doesn't list transverse Mercator as an option, rather it's a
rotated (oblique)
> Mercator. The equations for this and the other projections are definitely
sphere-based with no sign that
> the incoming terrain data (ex. USGS LULC) is being converted from the
ellipsoid-based datum to the
> sphere. 
> Melita
> Melita
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I also saw that it doesn't list transverse Mercator as an option. If they used
the rotated (oblique) Mercator option, and entered in 90 degrees as the rotation
parameter, would that be the equivalent of a transverse Mercator projection?  If
it was a rotated Mercator projection.. which proj4 projection do you think it
would be if it wasn't transverse mercator?
Hotine Oblique Mercator?
Laborde Oblique Mercator?
Oblique Mercator?
Swiss Oblique Mercator?
Rosenmund Oblique Mercator?

Also, I tried the proj4 string with the sphere radius defined:
proj -f "%f" +proj=tmerc +lat_0=47.5 +y_0=3175000.0 +x_0=3925000.0 +lon_0=-97.0
+k_0=1.0 +units=m +r=6371229.0 << EOF
-126.0869 19.61229
-125.6792 19.77242
-125.2703 19.93048
767826.309246   368215.750221
818695.246887   379008.554862
869407.646780   389577.252864

the output is supposed to be:
600000 600000
650000 600000
700000 600000

If I am understanding this correctly, I don't think that I have the correct or a
complete description of the parameters. Does that sound accurate?

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