<span class="Apple-style-span" style="border-collapse: collapse; font-family: arial, sans-serif; font-size: 13px; ">Hi,<div><br></div><div>This issue has been discussed many times before, so I'm trying to assess the current situation.</div>
<div><br></div><div>I'm a new user of Quantum GIS and Postgis which I understand uses Proj.4 for projections. I'm working with the RSO projection for Peninsular Malaysia both old and new definitions (EPSG:3168 and EPSG:3375). From my readings on various lists, RSO for Malaysia requires the +gamma parameter and the projection method is now classified by <a href="http://epsg-registry.org/" target="_blank" style="color: rgb(6, 88, 181); ">epsg-registry.org</a> as EPSG:9812 Hotine Oblique Mercator (Variant A). This means that the final rotation applied is at the natural origin as opposed to the center of projection which is Variant B (EPSG:9815)</div>
<div><br></div><div>In QGis, versions 1.6 and up in OSGeo4W, the default proj.4 string for EPSG:3168 and EPSG:3375 is without the +gamma parameter, so the projection is not correct. Looking at the OSGeo4W\share\proj\epsg file, gamma is indeed defined in there. So I'm confused where QGis srs.db is getting it's information from.</div>
<div><br></div><div>Creating a custom CRS in QGis with +gamma seems to have an effect, so the latest omerc.c does take into account the gamma parameter. However, the projection is still not quite correct. It looks like it is correctly aligned to north, but the x and y translation is off and I surmised that this has to do with the final center of rotation. I did an empirical correction with x_0 = false_easting + Uc sin(gc) and y_0 = false_northing + Uc cos(gc) approximately I think. Attached is a diagram of a comparison I did with different parameters. C is approximately the correct projection with a cadaster layer in EPSG:3384 overlayed at the bottom.</div>
<div><br></div><div>As proj.4 is used by many applications, my question is how and where can I get the projection parameters for RSO Malaysia corrected and how can the omerc projection be made to use variant A. I am advising a state government to standardize on QGis and PostGIS so there will be many users.</div>
<div><br></div><div>Thank you for any help and my apologies for bringing up this Malayan Monster again.</div><div><br></div><font color="#888888"><div><br clear="all"><span style="font-size: large; "><i><font face="garamond, serif"><b><font color="#FF6600">Hilmy</font></b></font></i></span></div>
</font></span><span style="font-size:large"><i><font face="garamond, serif"><b><font color="#FF6600">Hilmy</font></b></font></i></span><br>