[OSGeo Africa] Surveyor General Diagram - Mapping property boundary points

[Dr Wesley Roberts]

Dear Colleagues,



A friend has asked me to produce a map using a title deed SG document. The
property in question was surveyed in 1975 and it appears to make use of the
LO19 coordinate system. I am not that familiar with LO19 and am having some
trouble with defining a proj 4 projection in QGIS. I have produced a custom
CRS based on the this post by Gavin Flemming (
http://afrispatial.co.za/foss-gis/south-african-projections-in-foss-gis/).
All seems well until I look at the location, I can find it using ancillary
data. The coordinates on the title deed match only in the X domain (I have
swopped both the X and the Y as well as the sign) while the Y domain
appears to be “way out”. The SG title deed coordinate for one of the Y
points is -9105.30 (Constant +9 760 000,00) while the same location in the
QGIS returns a Y coordinate of around -3 769 758. Can anyone shed light on
why there is such a large difference between the SG Diagram and the actual
location?



1.       I am thinking that it might be something to do with the fact that
the property was surveyed in 1975, any ideas?

2.       I have used the following proj 4 definition – have I missed
something?



+proj=tmerc +lat_0=0 +lon_0=19 +k=1 +x_0=0 +y_0=0 +ellps=WGS84 +datum=WGS84
+units=m +no_defs



Any help on this matter would be greatly appreciated.



Regards,

Wesley



[image: Email_Signature]

Wesley Roberts, PhD

Geospatial Manager

Biocarbon Partners

wesley at biocarbonpartners.com

Cell RSA: +27 83 5355 646
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