[Proj] Rectified Skew Orthomorphic...

Michael Childs mike at globalmapper.com
Thu Feb 8 11:19:42 EST 2007

Thank you again for the information, but I am still not replicating the
results exactly. I am using the following proj4 string:

+proj=omerc +a=6378137.000 +b=6356752.314 +lat_0=4 +lonc=115 +x_0=0 +y_0=0
+alpha=53.315809950000 +k=0.9998400000 +no_uoff"

When I then convert from lat= "6 52 42.45022"; lon= "116 50 47.58835"; I get
coordinates of 796170.521, 759504.486 which is about 3.5 km away from the
expected test point. What proj4 parameter string are you using? Is there a
parameter that I am missing?


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: Thursday, February 08, 2007 8:44 AM
To: PROJ.4 and general Projections Discussions
Subject: Re: [Proj] Rectified Skew Orthomorphic...

> From: "Michael Childs"
> Date: Wed, 7 Feb 2007 17:06:41 -0600
> Subject: RE: [Proj] Rectified Skew Orthomorphic...

> Now that it seems I should be able to implement the Borneo/East Malaysia
> with the 'omerc' projection, does anyone have the exact parameters

The official Malayan GDM2000 Technical Manual has test points.
They are a bit sloppy wrt the old projections MRT and BT68: the test figures
are OK, but the parameters are unclear or wrong. I've figured them out.
For the modern GDM2000 projections the data are OK.

Test point and my results:
// BRSO (East Malaya)
lat= "6 52 42.45022"; lon= "116 50 47.58835";
// GRS80
lat0=4; lonc=115;
alfac= "53 18 56.91582"; gamma=asin(0.8)*rd; // rd: from radians to degrees
k0=0.99984; x0=0; y0=0;
Result: x,y = 793704.63096, 762081.04678
Technical Manual gives: 793704.631, 762081.047

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