Error converting WGS84 lat long to RSO Malaya (m) about proj

[proj4-bot]

Comment by warmerdam on 17 Apr 2009 14:36 UTC
Bjorn,

The error you are seeing looks like it might be a datum shifting issue, and I see the EPSG:3169 includes no datum shift parameters. I would suggest you look around to see if you can find any appropriate towgs84 shift values for the underlying datum (Kertau_RSO).

If you establish that there is an error in the projection aspect of the transformation, please feel free to reopen the ticket.

I do observe that with PROJ 4.6.0+ we get the values you expect:

cs2cs +proj=longlat +ellps=WGS84 +no_defs  +to +proj=omerc +lat_0=4  +lonc=102.25 +alpha=323.0257905 +k=0.99984 +x_0=804670.24 +y_0=0   +a=6377295.664 +b=6356094.667915204 +units=m +no_uoff +rot_conv +no_defs
101.77245333333333 3.1964683333333332
419628.13       353695.12 0.00

The difference is that PROJ 4.5.x and earlier will apply a change of ellipsoid if the input and output coordinate systems have different ellipsoids with no datum shift info. But PROJ 4.6.0 and later will not do so, so the transformation was effectively from long/lat Kertau_RSO datum. If that is what you wanted you could either upgrade to a newer PROJ.4, or use the following translation:

cs2cs +proj=longlat +a=6377295.664 +b=6356094.667915204 +no_defs  +to +proj=omerc +lat_0=4  +lonc=102.25 +alpha=323.0257905 +k=0.99984 +x_0=804670.24 +y_0=0   +a=6377295.664 +b=6356094.667915204 +units=m +no_uoff +rot_conv +no_defs