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<div class="moz-cite-prefix">Hi Wesley,<br>
That survey will be on the Cape datum, and not the Harte94 datum,
so you will have to use the Cape datum to throw it back to
LatLong, and then use the Harte94 Datum to push it forward to WG19<br>
<br>
The Lo19 and WG19 coordinates are much the same in that they both
are "Metres from Longitude 19degs" and "metres from the Equator"<br>
Note that if you use proj type definitions, they are +ve South (ie
South facing) - looking at the coords you are showing below, yours
are North facing. <br>
This 'North facing fix' was done because, especially in the old
days, CAD system could not handle South facing coords, so that was
rectified by simply multiplying each column of numbers by "-1".<br>
<br>
I have a 'C' program somewhere that I wrote many years back, that
handles this - but maybe someone on this list has done this with
proj & QGIS.<br>
Although I haven't had to do this for many years, I'd be
interested in a QGIS solution.<br>
<br>
HTH,<br>
Zoltan<br>
<br>
<br>
On 2014/09/29 14:37, Dr Wesley Roberts wrote:<br>
</div>
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<p class="MsoNormal">Dear Colleagues,</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">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 (<a moz-do-not-send="true"
href="http://afrispatial.co.za/foss-gis/south-african-projections-in-foss-gis/">http://afrispatial.co.za/foss-gis/south-african-projections-in-foss-gis/</a>).
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?</p>
<p class="MsoNormal"> </p>
<p class="MsoListParagraph" style=""><span style="">1.<span
style="font:7.0pt "Times New Roman""> </span></span>I
am thinking that it might be something to do with the fact
that the property was surveyed in 1975, any ideas?</p>
<p class="MsoListParagraph" style=""><span style="">2.<span
style="font:7.0pt "Times New Roman""> </span></span>I
have used the following proj 4 definition – have I missed
something?</p>
<p class="MsoListParagraph"> </p>
<p class="MsoNormal">+proj=tmerc +lat_0=0 +lon_0=19 +k=1 +x_0=0
+y_0=0 +ellps=WGS84 +datum=WGS84 +units=m +no_defs</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Any help on this matter would be greatly
appreciated.</p>
<p class="MsoNormal"> </p>
<p class="MsoNormal">Regards,</p>
<p class="MsoNormal">Wesley</p>
<p class="MsoNormal"> </p>
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<p class="MsoNormal" style="border:none;padding:0in"><img
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src="cid:part2.04030900.04020803@geograph.co.za"
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</div>
<p class="MsoNormal">Wesley Roberts, PhD</p>
<p class="MsoNormal">Geospatial Manager</p>
<p class="MsoNormal">Biocarbon Partners</p>
<p class="MsoNormal"><a moz-do-not-send="true"
href="mailto:wesley@biocarbonpartners.com">wesley@biocarbonpartners.com</a></p>
<p class="MsoNormal">Cell RSA: +27 83 5355 646</p>
<p class="MsoNormal"> </p>
</div>
<br>
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<pre class="moz-signature" cols="72">--
===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
GIS and Photogrammetric Services
P.O. Box 7, Muizenberg 7950, South Africa.
Mobile: +27-83-6004028
Fax: +27-86-6115323 <a class="moz-txt-link-abbreviated" href="http://www.geograph.co.za">www.geograph.co.za</a>
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