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--></style></head><body bgcolor="white" lang="EN-US" link="blue" vlink="purple"><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:#1f497d">Hi All,</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 so close now. I have taken both Gavin’s and Zoltan’s advice and used the custom CRS definition using the precision conversion factor suggested by Zoltan.</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 able to view the coordinate points in QGIS and can see that they are almost in the correct location, however, there appears to be some sort of transformation error. The best way to describe the error is to imagine points as a rectangle lying at a 45 degree angle. With the current CRS setup the points which should be at the top are now at the bottom and the points at the bottom are at the top. Difficult to explain without a graphic and I doubt that the mailing list will accept graphics in images. The points need to be rotated 180 degrees through the vertical, if that makes any sense.</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 can mail a grphic off list should this not make sense.</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,</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><div><div style="border:none;border-top:solid #e1e1e1 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext">From:</span></b><span style="font-size:11.0pt;font-family:"Calibri","sans-serif";color:windowtext"> <a href="mailto:africa-bounces@lists.osgeo.org">africa-bounces@lists.osgeo.org</a> [mailto:<a href="mailto:africa-bounces@lists.osgeo.org">africa-bounces@lists.osgeo.org</a>] <b>On Behalf Of </b>Zoltan Szecsei<br><b>Sent:</b> Monday, September 29, 2014 6:45 PM<br><b>To:</b> <a href="mailto:africa@lists.osgeo.org">africa@lists.osgeo.org</a><br><b>Subject:</b> Re: [OSGeo Africa] Surveyor General Diagram - Mapping property boundary points</span></p></div></div><p class="MsoNormal"> </p><div><p class="MsoNormal">On 2014/09/29 18:42, Zoltan Szecsei wrote:</p></div><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><div><p class="MsoNormal"><span style="color:#009900">Cape or English feet?<br>See below:</span><br><br>On 2014/09/29 16:24, Gavin Fleming wrote:</p></div><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><div><p class="MsoNormal">Hi Wesley<br><br>If you load the coordinates with the correct CRS definition in QGIS you shouldn't need to swap signs or axes. Any coordinates you get from a survey diagram will be south-oriented (SO). Just apply an appropriate SO CRS definition. <br><br>These are pre-defined options available in QGIS relating to 'LO19':<br><br>LO19 Cape datum (m) south-oriented: EPSG 22279<br>LO19 Cape datum (m) north-oriented: South African CRS : CAPE_NO_19<br>LO19 WGS84 (or Hartebeesthoek94) datum (m) south-oriented: EPSG 2048<br>LO19 WGS84 (or Hartebeesthoek94) datum (m) north-oriented: South African CRS : HBK_NO_19<br><br>If your Y coordinates are indeed positive and in the region of 9 million then I'd venture they are in Cape Feet and south-oriented, in which case there's no pre-defined CRS. </p></div></blockquote><p class="MsoNormal"><span style="color:#009900">I think at some point Natal was using English feet - the rest of South Africa: Cape feet<br>You might want to add far more precision to the conversion factor, though:<br>9760000 * .314858 = 3 073 014.08<br>9760000 * .31485557516 = 3 072 990.4135<br><br>That's a 23.67m difference.<br><br>Regards,<br>Zoltan</span><br><br><br></p><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><div><p class="MsoNormal" style="margin-bottom:12.0pt"><br>So create a custom CRS using this proj4 definition. Call it something like 'LO19 Cape SO Cape feet'</p><blockquote style="margin-top:5.0pt;margin-bottom:5.0pt"><p class="MsoNormal"><span style="font-size:11.5pt;font-family:"Arial","sans-serif"">+proj=tmerc +lat_0=0 +lon_0=<b>19</b> +k=1 +x_0=0 +y_0=0 +axis=wsu +a=6378249.145 +b=6356514.966398753 +towgs84=-136,-108,-292,0,0,0,0 <b>+to_meter=0.314858</b> +no_defs</span></p></blockquote><p class="MsoNormal" style="margin-bottom:12.0pt"><br>+axis=wsu makes it south-facing<br>+towgs84=.... specifies the Cape to WGS84 datum transformation<br>+to_meter=... specifies the cape feet to metre conversion. <br><br>btw the example on my (old) website is for data in north-oriented data on the WGS84 datum, in metres. It was also written before SA CRS definitions were available in GIS software. The QGIS CRS to use for the same CRS now would be "South African CRS : HBK_NO_19". <br><br>Gavin</p></div></blockquote></blockquote><p class="MsoNormal"><br><br></p><pre>-- </pre><pre> </pre><pre>===========================================</pre><pre>Zoltan Szecsei PrGISc [PGP0031]</pre><pre>Geograph (Pty) Ltd.</pre><pre>GIS and Photogrammetric Services</pre><pre> </pre><pre>P.O. Box 7, Muizenberg 7950, South Africa.</pre><pre> </pre><pre>Mobile: +27-83-6004028</pre><pre>Fax: +27-86-6115323 <a href="http://www.geograph.co.za">www.geograph.co.za</a></pre><pre>===========================================</pre></div></body></html>