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

[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?


Regards
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