1

I am looking at an old map (the 1975 layer) and they only have three parameters for their projection:

  • Projection: Rectified Skew Orthomorphic (Metric Grid)
  • Spheroid: Everest
  • Origin: 4.00 N, 102.25 E

I've been trying to make a custom proj4-string in QGIS 3.4 but it keeps returning that it's invalid.

Here's the string:

+proj=omerc +lat_0=4.0 +lon_0=102.25 +ellps=evrst69 +units=m +no_defs

Does anyone know what else I'm missing to make the string a valid projection?

There isn't much else on the map, unless there actually is something on the map that I'm completely missing.

For future reference, what are the things that I need to look out for from old maps such as the one in the link above to try and make the custom proj4-string?

4

In QGIS 3.18 The projection is given in the picklist for Malaysia

Everest_Modified_1969_RSO_Malaya_Meters

Proj4

+proj=omerc +no_uoff +lat_0=4 +lonc=102.25 +alpha=-36.974209437118 +gamma=-36.869897645844 +k=0.99984 +x_0=804670.24 +y_0=0 +ellps=evrst69 +units=m +no_defs

The second part of the question: when looking for old coordinate systems look in https://www.asprs.org/asprs-publications/grids-and-datums here you'll find the columns by Clifford Mugnier, describing old coordinate systems for a lot of countries. Singapore is https://www.asprs.org/wp-content/uploads/2012/05/01-2006-singapore.pdf

1
  • +3 for giving the correct proj4-string, actually finding the existing projection, AND providing a handy resource on how to find old coordinate systems.
    – Lalochezia
    Jul 11 at 21:05
3

QGIS prefers WKT format, not Proj4. Your definition is missing, at minimum, "Azimuth", "False Easting" and "False Northing". Here's an example of a Custom Variant 2 Hotine Oblique Mercator Projection that I just created in QGIS:

PROJCS["YellowstoneRiver_OMerc_AC", GEOGCS["GCS_NAD_1983_2011", DATUM["D_NAD_1983_2011", SPHEROID["GRS_1980",6378137.0,298.257222101]], PRIMEM["Greenwich",0.0], UNIT["Degree",0.0174532925199433]], PROJECTION["Hotine_Oblique_Mercator_Azimuth_Center"], PARAMETER["latitude_of_center",47.05], PARAMETER["longitude_of_center",-104.65], PARAMETER["azimuth",31.0], PARAMETER["rectified_grid_angle",31.0], PARAMETER["scale_factor",1.000105], PARAMETER["false_easting",656167.979], PARAMETER["false_northing",738188.976], UNIT["foot",0.3048], AXIS["X",EAST], AXIS["Y",NORTH]]

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.