Geographic Information Systems Asked on July 16, 2021
I am looking at an old map (the 1975 layer) and they only have three parameters for their projection:
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?
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
Correct answer by Hans Erren on July 16, 2021
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]]
Answered by Pointdump on July 16, 2021
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