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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>
<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>
<meta charset="utf-8">
<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>
On 29/09/2014 16:03, Dr Wesley Roberts wrote:<br>
</div>
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<p class="MsoNormal"><span style="color:#1f497d">Many thanks
Aslam,</span></p>
<p class="MsoNormal"><span style="color:#1f497d"> </span></p>
<p class="MsoNormal"><span style="color:#1f497d">Will make the
change and see where I end up.</span></p>
<p class="MsoNormal"><span style="color:#1f497d"> </span></p>
<p class="MsoNormal"><span style="color:#1f497d">Regards,</span></p>
<p class="MsoNormal"><span style="color:#1f497d">Wesley</span></p>
<p class="MsoNormal"><span style="color:#1f497d"> </span></p>
<div>
<div style="border:none;border-bottom:solid windowtext
1.5pt;padding:0in 0in 1.0pt 0in">
<p class="MsoNormal" style="border:none;padding:0in"><span
style="color:#1f497d"><br>
</span></p>
</div>
<p class="MsoNormal"><span style="color:#1f497d">Wesley
Roberts, PhD</span></p>
<p class="MsoNormal"><span style="color:#1f497d">Geospatial
Manager</span></p>
<p class="MsoNormal"><span style="color:#1f497d">Biocarbon
Partners</span></p>
<p class="MsoNormal"><span style="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="color:#1f497d">Cell RSA: +27
83 5355 646</span></p>
</div>
<p class="MsoNormal"><span style="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="color:windowtext">From:</span></b><span
style="color:windowtext"> <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>Aslam Parker<br>
<b>Sent:</b> Monday, September 29, 2014 3:56 PM<br>
<b>To:</b> <a moz-do-not-send="true"
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"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">Hi All</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">Just as a quick recap,
the SG diagrams has a system of westings (y) and southings
(x), where:</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">westings (y) is
the distance from the closest odd Lo(Central Meridian)
and southings (x) is the distance from the equator</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">In SA the y range from
110 000m to approx 110 000 m and, x ranges from 2 2 00
000 in Limpopo to 3 800 000 (Cape Aghulus).</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">When there are values
with constants such as +9 760 000, I would automatically
assume that the unit of measure is Cape Feet and all
coordinates and constants needs to be converted to meters.</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">The easiest way (for a
non surveyor) to transform Cape Datum data (modified
Clarke 1880) to Hartebeesthoek94 (WGS84) is by using the
NTV2 transformation grid that QGIS can also use. If you
correctly read data and define it as Cape Datim, you can
reproject pretty accurately into Hartebeesthoek94 using
this transformation method.</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">Please see <a
moz-do-not-send="true"
href="http://www.ee.co.za/article/datum-transformations-using-the-ntv2-grid.html">http://www.ee.co.za/article/datum-transformations-using-the-ntv2-grid.html</a></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> </span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">I hope this helps</span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""><br>
<br>
>>> Zoltan Szecsei <<a moz-do-not-send="true"
href="mailto:zoltans@geograph.co.za">zoltans@geograph.co.za</a>>
9/29/2014 3:05 PM >>></span></p>
</div>
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">AAaargh! WGS84<br>
(I'll go away, now)<br>
On 2014/09/29 15:03, Zoltan Szecsei wrote:</span></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">Hi again,<br>
Sorry - forgot to add:<br>
If you don't do the re-projection, your survey diagram
will sit approx 296m N/S and 50m E/W away from your </span><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif";color:#990000">WGS95</span><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""> orthophoto.<br>
If it sits only some 50m or so away from where it should
sit, then it is likely that the Datum shift (between
Cape & Harte94) wasn't applied.<br>
<br>
Wow - that's the best my memory serves me - I last did
this stuff in 2003.<br>
Perhaps there is a surveyor on this list that can add
to, or correct, what I have suggested?<br>
<br>
Wesley: If you're still stuck in a day or so, contact me
off list & we can get it sorted better if I have the
data set from you.<br>
<br>
Regards,<br>
Z<br>
<br>
<br>
On 2014/09/29 14:47, Zoltan Szecsei wrote:</span></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<div>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif"">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:</span></p>
</div>
<blockquote style="margin-top:5.0pt;margin-bottom:5.0pt">
<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">1.<span
style="font-size:7.0pt;font-family:"Times New
Roman","serif""> </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">2.<span
style="font-size:7.0pt;font-family:"Times New
Roman","serif""> </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>
<div style="border:none;border-bottom:solid windowtext
1.5pt;padding:0in 0in 1.0pt 0in">
<p class="MsoNormal"><br>
</p>
</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>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
UI","sans-serif""><br>
<br>
<br>
</span></p>
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<br>
<br>
</span></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 moz-do-not-send="true" href="http://www.geograph.co.za">www.geograph.co.za</a></pre>
<pre>===========================================</pre>
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<br>
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<br>
<br>
</span></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 moz-do-not-send="true" href="http://www.geograph.co.za">www.geograph.co.za</a></pre>
<pre>===========================================</pre>
<p class="MsoNormal"><span
style="font-size:10.0pt;font-family:"Segoe
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<br>
<br>
</span></p>
<pre>_______________________________________________</pre>
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<br>
<br>
</span></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 moz-do-not-send="true" href="http://www.geograph.co.za">www.geograph.co.za</a></pre>
<pre>===========================================</pre>
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