[Qgis-developer] On-The-Fly CRS Transformation Does Not Apply +no_off Parameter

[Andre Joost]

Am 28.04.2013 07:21, schrieb Hilmy Hashim:
> Hello all,
>
>
> This query is about a discrepancy between projection results using the *Custom
> CRS Test* and *on-the-fly* transformation, and not about RSO per se.
>
>
> The Proj4 parameters for GDM2000 / Peninsula RSO (EPSG:3375) as given by
> epsg_tr.py (GDAL 1.9.2) are:
>
> +proj=omerc +lat_0=4 +lonc=102.25 +alpha=323.0257964666666 +k=0.99984
> +x_0=804671 +y_0=0 +gamma=323.1301023611111 +ellps=GRS80 +units=m +no_defs
>
> This Malaysian projection requires the +no_off or *+no_uoff* flag (both
> works) for rotation at the natural origin as of proj 4.8. To test, I
> created a custom CRS based on GDM2000 / Peninsula RSO adding this flag.
> However, there seems to be some discrepancy between the on-the-fly derived
> results and the Test in the Custom CRS definition dialog.
>
>
> I set the project CRS as the custom CRS I created and added the test point
> in WGS84.
>
> Test points: *1.827764875* deg N, *103.640259872222* deg E (WGS84 EPSG:4326)
>
> Expected results: Northing *202,122.062* m, Easting *627,096.132* m
> (EPSG:3375)
>
> *The test points and projected coordinates are taken from the GDM2000
> Technical Manual published by the Department of Survey and Mapping Malaysia.
> *
>
> *Test results (standard EPSG:3375)*:
>
> cs2cs — -240332.04, 958936.71
>
> QGIS Master (13d35ac) On-the-fly derived: Y = -240,332.0326, X =
> 958,936.7057
>
> QGIS Master (13d35ac) Custom CRS Test:* -240,332.0326* N, *958,936.7057* E
>
> QGIS 1.8 On-the-fly: projected coordinates not derived
>
> QGIS 1.8 Custom CRS Test: -240,332.0326 N, 958,936.7057 E
>
> *Test results (with +no_off flag)*:
>
> cs2cs — 202122.06,  627096.13
>
> QGIS Master (13d35ac) On-the-fly derived: Y =* -240,332.0326*, X = *
> 958,936.7057*
>
> QGIS Master (13d35ac) Custom CRS Test: *202,122.0625* N, *627,096.1317* E
>
> QGIS 1.8 On-the-fly: projected coordinates not derived
>
> QGIS 1.8 Custom CRS Test: 202,122.0625 N, 627,096.1317 E
>
>
> It looks like the Custom CRS Definition Test dialog is giving the correct
> result, but the on-the-fly transformation is ignoring the +no_off flag.
>
>
> Is the on-the-fly transformation using a different transformation process
> and reading the proj4 parameters differently, or am I going about this
> wrongly?

I made some tests with the similar Michigan omerc projections and ran 
into the same problem:
http://trac.osgeo.org/gdal/ticket/4910

It looks like it is a GDAL problem.

HTH,
André Joost