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<div class="moz-cite-prefix">Hi All,<br>
The "missing step" is the Datum shift.<br>
If you do it manually, then the sequence is "Cape Lo19 to LatLong
<=Datum shift=>LatLong to Harte94 WG19"<br>
If with QGIS you specify your original CRS n Cape Lo19 and your
Tagert CRS on Harte94 WG19 the QGIS should handle the Datum shift,
and it will seem transparent to you.<br>
<br>
The "Survey Convention" is South Africa is to use the "Lo" prefix
to suggest Cape Datum, and the "WG" prefix to show WGS84, Harte94
Datum. The numeric value after the "Lo" and the "WG" is the
longitude of the central meridian.<br>
<br>
HTH,<br>
Zoltan<br>
<br>
<br>
On 2014/09/29 15:20, Dr Wesley Roberts wrote:<br>
</div>
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi
Sarel,</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">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?</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">So,
my workflow is </span></p>
<p class="MsoListParagraph" style=""><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><span
style="">1.<span style="font:7.0pt "Times New
Roman""> </span></span></span><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Generate
text file with X and Y coordinates</span></p>
<p class="MsoListParagraph" style=""><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><span
style="">2.<span style="font:7.0pt "Times New
Roman""> </span></span></span><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Open
in QGIS using delimited text file import </span></p>
<p class="MsoListParagraph" style=""><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><span
style="">3.<span style="font:7.0pt "Times New
Roman""> </span></span></span><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Assign
a suitable projection to the mapped points (LO19 Cape Datum)</span></p>
<p class="MsoListParagraph"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">………An
intermediate step……… <- Think of the maths cartoon where
the prof says “and then a miracle happens”</span></p>
<p class="MsoListParagraph" style=""><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><span
style="">4.<span style="font:7.0pt "Times New
Roman""> </span></span></span><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Re-project
to WGS 84\</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">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?</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Regards,</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Wesley</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><span
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id="Picture_x0020_1"
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<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Wesley
Roberts, PhD</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Geospatial
Manager</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Biocarbon
Partners</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"><a
moz-do-not-send="true"
href="mailto:wesley@biocarbonpartners.com"><span
style="color:#0563c1">wesley@biocarbonpartners.com</span></a></span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Cell
RSA: +27 83 5355 646</span></p>
<p class="MsoNormal"><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d"> </span></p>
<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif"">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri","sans-serif"">
<a moz-do-not-send="true"
href="mailto:africa-bounces@lists.osgeo.org">africa-bounces@lists.osgeo.org</a>
[mailto:<a moz-do-not-send="true"
href="mailto:africa-bounces@lists.osgeo.org">africa-bounces@lists.osgeo.org</a>]
<b>On Behalf Of </b>S Coetzer<br>
<b>Sent:</b> Monday, September 29, 2014 3:05 PM<br>
<b>To:</b> Africa local chapter discussions<br>
<b>Subject:</b> Re: [OSGeo Africa] Surveyor General Diagram
- Mapping property boundary points</span></p>
<p class="MsoNormal"> </p>
<div>
<div>
<div>
<div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Hi
Wesly</p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt">Zoltan
is correct, use Cape datum for 1975 data, I think the
EPSG code is: 22279</p>
</div>
<p class="MsoNormal" style="margin-bottom:12.0pt">In QGIS,
use 22279 to filter your CRS and you'lle find it.</p>
</div>
<p class="MsoNormal">Good luck.</p>
</div>
<div>
<p class="MsoNormal"><br clear="all">
</p>
<div>
<p class="MsoNormal">Sarel Coetzer </p>
</div>
<p class="MsoNormal"> </p>
<div>
<p class="MsoNormal">On Mon, Sep 29, 2014 at 2:37 PM, Dr
Wesley Roberts <<a moz-do-not-send="true"
href="mailto:wesley@biocarbonpartners.com"
target="_blank">wesley@biocarbonpartners.com</a>>
wrote:</p>
<blockquote style="border:none;border-left:solid #cccccc
1.0pt;padding:0in 0in 0in
6.0pt;margin-left:4.8pt;margin-right:0in">
<div>
<div>
<p class="MsoNormal" style="">Dear Colleagues,</p>
<p class="MsoNormal" style=""> </p>
<p class="MsoNormal" style="">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/"
target="_blank">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" style=""> </p>
<p>1.<span style="font-size:7.0pt"> </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>2.<span style="font-size:7.0pt"> </span>I
have used the following proj 4 definition – have I
missed something?</p>
<p> </p>
<p class="MsoNormal" style="">+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" style=""> </p>
<p class="MsoNormal" style="">Any help on this matter
would be greatly appreciated.</p>
<p class="MsoNormal" style=""> </p>
<p class="MsoNormal" style="">Regards,</p>
<p class="MsoNormal" style="">Wesley</p>
<p class="MsoNormal" style=""> </p>
<div style="border:none;border-bottom:solid windowtext
1.5pt;padding:0in 0in 1.0pt 0in">
<p class="MsoNormal" style=""><img id="_x0000_i1025"
src="cid:part1.00070106.08050203@geograph.co.za"
alt="Email_Signature" width="334" border="0"
height="103"></p>
</div>
<p class="MsoNormal" style="">Wesley Roberts, PhD</p>
<p class="MsoNormal" style="">Geospatial Manager</p>
<p class="MsoNormal" style="">Biocarbon Partners</p>
<p class="MsoNormal" style=""><a
moz-do-not-send="true"
href="mailto:wesley@biocarbonpartners.com"
target="_blank">wesley@biocarbonpartners.com</a></p>
<p class="MsoNormal" style="">Cell RSA: +27 83 5355
646</p>
<p class="MsoNormal" style=""> </p>
</div>
</div>
<p class="MsoNormal"><br>
_______________________________________________<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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