I have a map here with coordinates from the Schwarzeck Map Datum Format 1903. They have the following format:
y: 41 944,31 x: 363 810,71
I want these points to be pictured in QGIS...
How is it done?
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The official CRS paramters can be found here: http://www.mme.gov.na/gsn/nam-map-system.htm.
So it should be Albers Equal Area or LO Gauss conformal. Qgis only offers EPSG 4293 (lat/lon) and EPSG 29333 (UTM 33S). Both do not match with the given example.
You may try one of these: http://spatialreference.org/ref/?search=Schwarzeck
For the local LO 22/17 system EPSG 29377:
The page does not have a proj string, but OGC WKT. I saved it to 29377.prf, and converted the points with gdaltransform from OSGeo4W:
gdaltransform -s_srs 29377.prf -t_srs EPSG:4326 < input.txt > out.txt
Input Y X without minus, and blanks as delimiters. After adding to the Output file a line
E S Z
you can add the file as delimited text layer with blanks as delimiters, marking the E and S column as X and Y. Layer CRS should be set to EPSG:4326.
For LO 22/17, you can test this proj string under settings/custom CRS:
+proj=tmerc +lat_0=-22 +lon_0=17 +k=1 +x_0=0 +y_0=0 +a=6377397.155 +rf=299.1528128 +towgs84=616,97,-251,0,0,0,0 +units=m +no_defs
(Not sure where to bring the "German legal meter" in)
You can add a line with
before your data, and import in Qgis as delimited text with blank as delimiter. Then apply the user-created CRS to that layer.
Comparing both with Bing Aerial map in Qgis Openstreetmap plugin looks as follows. The difference between Solution A and B is about 18 cm. Openstreetmap even knows the place name Ombili ;-)
I think the coordinates should both be negative. "Transverse Marcator - south orientated" should have positive values to the south and west of the reference point (-22/+17). But until someone comes up with a correct projection string, it is easier to swap plus/minus on the input side. This would also apply to the WKT format given at spatialreference.org.
You need to know the exact parameters of this coordinat system, for instance longitud of origin, false easting, false northing etc. Check this
Once you know them, you can try defining a custom crs at settings/custom CRS. You can test some points in lat long wgs84 in this place also. CRS definition must be in proj4 format. You can test some points in lat long wgs84. The only problem could be your datum, though...
hope it helps