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

[Dr Wesley Roberts]

Hi Sarel,



Many thanks for the input. I have found the specific EPSG and as before the
same location appears to have different coordinates to those specified on
the surveyors diagram. I think I am missing a step here. Based on Zoltans
response I think I need an intermediate step to get the points into the
correct location, is this correct?



So, my workflow is

1.       Generate text file with X and Y coordinates

2.       Open in QGIS using delimited text file import

3.       Assign a suitable projection to the mapped points (LO19 Cape Datum)

………An intermediate step……… <- Think of the maths cartoon where the prof
says “and then a miracle happens”

4.       Re-project to WGS 84\



I am still lost when it comes to the north facing vs south facing
projection and how I get the proj to match the coordinates on the SG
diagram. Could this not al be a change in the constant?



Regards,

Wesley





[image: Email_Signature]

Wesley Roberts, PhD

Geospatial Manager

Biocarbon Partners

wesley at biocarbonpartners.com

Cell RSA: +27 83 5355 646



*From:* africa-bounces at lists.osgeo.org [mailto:
africa-bounces at lists.osgeo.org] *On Behalf Of *S Coetzer
*Sent:* Monday, September 29, 2014 3:05 PM
*To:* Africa local chapter discussions
*Subject:* Re: [OSGeo Africa] Surveyor General Diagram - Mapping property
boundary points



Hi Wesly

Zoltan is correct, use Cape datum for 1975 data, I think the EPSG code is:
22279

In QGIS, use 22279 to filter your CRS and you'lle find it.

Good luck.


Sarel Coetzer



On Mon, Sep 29, 2014 at 2:37 PM, Dr Wesley Roberts <
wesley at biocarbonpartners.com> wrote:

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




_______________________________________________
Africa mailing list
Africa at lists.osgeo.org
You can UNSUBSCRIBE at http://lists.osgeo.org/mailman/listinfo/africa
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.osgeo.org/pipermail/africa/attachments/20140929/1f67d43a/attachment-0001.html>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: image001.jpg
Type: image/jpeg
Size: 6188 bytes
Desc: not available
URL: <http://lists.osgeo.org/pipermail/africa/attachments/20140929/1f67d43a/attachment-0001.jpg>