[Proj] Rectified Skew Orthomorphic...

Michael Childs mike at globalmapper.com
Wed Feb 7 18:06:41 EST 2007

Thanks for the information.  I had completely missed the February and later
archives, I didn't realize that I was only looking at January so I thought I
had the complete thread.

Now that it seems I should be able to implement the Borneo/East Malaysia RSO
with the 'omerc' projection, does anyone have the exact parameters required?
I have some from EPSG, but I can get out the exact same result as EPSG #7
listed as a sample, but I'm not 100% certain that is correct anyway based on
the discussion from 2004. Does anyone have any actual sample points in both
Borneo RSO and Lat/Lon so that I can verify my conversion?


Global Mapper Software LLC
mike at globalmapper.com

-----Original Message-----
From: proj-bounces at lists.maptools.org
[mailto:proj-bounces at lists.maptools.org] On Behalf Of Oscar van Vlijmen
Sent: Wednesday, February 07, 2007 3:38 PM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Rectified Skew Orthomorphic...

> From: "Michael Childs"
> Date: Wed, 7 Feb 2007 11:50:50 -0600
> Subject: [Proj] Rectified Skew Orthomorphic...

> I am trying to use Proj4 v4.4.9 to implement RSO support as described
> from a 2004 thread, but it does not appear that the changes discussed in
> thread ever made it into Proj4. Am I missing something or did these
> never get made? Does anyone have a copy of the code that implemented the
> 'gamma_c' parameter for the 'omerc' projection?

I am inclined to believe that all useful omerc RSOs can be done with
libproj/proj with the natural x_0, y_0 and the no_off/no_uoff flag set.
Libproj is more flexible (or transparent) with respect to the alpha and
gamma parameters, but proj does its best.
Point is, as mr. Evenden pointed out in a posting dated Feb 6, 2004, that
you don't need both alpha and gamma. Manuals and parameter files often
specify both, but for reasonable projections you only need one; the other is
calculated automatically.
It could be that proj is somewhat more difficult to handle because it
doesn't recognize a gamma. But the gamma is calculated from the specified
alpha. If you need to rotate the u,v coordinates over gamma instead of
alpha, you can use the rot_conv flag in proj. One might want to study Table
4 in the proj manual proj.4.3.pdf.

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