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<div class="moz-cite-prefix">On 2014/09/29 18:42, Zoltan Szecsei
wrote:<br>
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<blockquote cite="mid:54298BE9.2070900@geograph.co.za" type="cite">
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<div class="moz-cite-prefix"><font color="#009900">Cape or English
feet?<br>
See below:</font><br>
<br>
On 2014/09/29 16:24, Gavin Fleming wrote:<br>
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<blockquote cite="mid:54296B93.3080306@kartoza.com" type="cite">
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<div class="moz-cite-prefix">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. <br>
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<font 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</font><br>
<br>
<blockquote cite="mid:54296B93.3080306@kartoza.com" type="cite">
<div class="moz-cite-prefix"> <br>
So create a custom CRS using this proj4 definition. Call it
something like 'LO19 Cape SO Cape feet'<br>
<br>
<blockquote><b style="font-weight:normal;"
id="docs-internal-guid-63de80ab-c1b8-80c2-e1a2-4536c7725f80"><span
style="font-size:15px;font-family:Arial;color:#000000;background-color:transparent;font-weight:normal;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap;">+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 </span><span
style="font-size:15px;font-family:Arial;color:#000000;background-color:transparent;font-weight:bold;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap;">+to_meter=0.314858</span><span
style="font-size:15px;font-family:Arial;color:#000000;background-color:transparent;font-weight:normal;font-style:normal;font-variant:normal;text-decoration:none;vertical-align:baseline;white-space:pre-wrap;">
+no_defs</span></b><br>
</blockquote>
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<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<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>
===========================================</pre>
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