[QGIS-ZA-user] qgis-za-user Digest, Vol 53, Issue 2

Tue Apr 2 02:34:01 PDT 2024

Thank you Ryk

Could you please attach the spreadsheet.

I have learnt by now that if I flip the X,Y coordinates and then use EPSG
22287 in QGIS, I land up in the correct area (more or less on the correct
farm). That solution I have learnt from the PlanetGIS documentation. An
error of 300m should be acceptable for my purpose (for now).

Best regards

Jordaan Fouche
Portion 11
Van Reenen Country Estate
Van Reenen
3372
Republic of South Africa

Tel: +27 (0)82 555 4227

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Today's Topics:

   1. Re: Coordinate conversion from Cape Datum Lo27? to EGS 84
      (Ryk Taljaard)

----------------------------------------------------------------------

Message: 1
Date: Tue, 2 Apr 2024 10:32:58 +0200
From: "Ryk Taljaard" <ryk at boundaryhunter.co.za>
To: "'South Africa QGIS user group'" <qgis-za-user at lists.osgeo.org>
Subject: Re: [QGIS-ZA-user] Coordinate conversion from Cape Datum
	Lo27? to EGS 84
Message-ID: <00be01da84d8$5e964640$1bc2d2c0$@co.za>
Content-Type: text/plain; charset="utf-8"

I use the attached spreadsheet for calculation of CAPE to WGS84
transformation of coordinate values, for data obtained from specific SG
diagrams.

TRIG 1 is the trig beacon closest to the study area and the resulting values
used for the relevant transformation calculation.
TRIG 2 is 2nd closest to the study are and used only for indication of any
possible gross error.
Take note of:
(1) The pos/neg switch of coordinate values required for GIS purposes and
(2) Beware of the study area, TRIG1 and TRIG2 being located in different
LO-systems.

Mowbray makes available the localities of all TRIG beacons in KML format, as
well as the coordinates of all TRIG beacons in both Clarke1880 and WGS84 in
TXT format, to use as input to the attached spreadsheet.

Best regards

Ryk Taljaard
Boundary Hunter
Mobile: 082 895 2906
1 Joerning Street * Paarl * 7646 * SOUTH AFRICA
Web:   <http://www.boundaryhunter.co.za/> www.boundaryhunter.co.za * Email:
<mailto:ryk at boundaryhunter.co.za> ryk at boundaryhunter.co.za

From: qgis-za-user [mailto:qgis-za-user-bounces at lists.osgeo.org] On Behalf
Of Gavin Fleming via qgis-za-user
Sent: Tuesday, 02 April 2024 09:51
To: South Africa QGIS user group
Cc: Gavin Fleming
Subject: Re: [QGIS-ZA-user] Coordinate conversion from Cape Datum Lo27? to
EGS 84

Hi Jordan and thanks FC

I?m not sure how FC did the projection / transformation but you can use
QGIS, proj or a number of other tools.

An issue to be aware of is that no GIS will do an accurate datum
transformation from Cape to WGS84/Hartebeeshoek94 since there are different
errors all over the country, as much as 300m. If you need accuracy, rather
speak to a land surveyor, who can do a local transformation taking into
account the known errors. 

Gavin

On 22 Mar 2024, at 09:25, Jordaan Fouche via qgis-za-user
<qgis-za-user at lists.osgeo.org> wrote:

Thank you FC, what software did you use to do the transformation?

Could you explain in a bit more detail?

Jordaan Fouche
Portion 11
Van Reenen Country Estate
Van Reenen
3372
Republic of South Africa

Tel: +27 (0)82 555 4227

From: FC Basson <FC.Basson at westerncape.gov.za>
Sent: Thursday, March 21, 2024 8:26 PM
To: qgis-za-user at lists.osgeo.org
Cc: j.fouche9 at gmail.com
Subject: Re: [QGIS-ZA-user] Coordinate conversion from Cape Datum Lo27? to
EGS 84

Just a slight edit to the Google Maps link:
https://maps.app.goo.gl/VVS9XDfhjp88dXw97

And if you prefer OSM:
https://www.openstreetmap.org/?mlat=-26.82808180999955
<https://www.openstreetmap.org/?mlat=-26.82808180999955&mlon=28.591287809999
518#map=12/-26.8281/28.5913>
&mlon=28.591287809999518#map=12/-26.8281/28.5913

  _____  

From: qgis-za-user <qgis-za-user-bounces at lists.osgeo.org> on behalf of FC
Basson via qgis-za-user <qgis-za-user at lists.osgeo.org>
Sent: 21 March 2024 20:09
To: qgis-za-user at lists.osgeo.org <qgis-za-user at lists.osgeo.org>
Cc: FC Basson <FC.Basson at westerncape.gov.za>; j.fouche9 at gmail.com
<j.fouche9 at gmail.com>
Subject: Re: [QGIS-ZA-user] Coordinate conversion from Cape Datum Lo27? to
EGS 84

I was able to locate the farm and can confirm that the coordinate should be
in LO 29.  
<image001.png>
For GIS purposes, we use the rotated coordinate system, so the coordinates
should be X: -40600, Y: -2968350, which converts to geographic coordinate of
Lat: -26.828082, Lon: 28.591288, if you assume the input datum is Cape.  And
here is a link to the location in Google Maps:
https://maps.app.goo.gl/bEwU4pMa35Db2gpNA

Regards

FC Basson

  _____  

From: qgis-za-user <qgis-za-user-bounces at lists.osgeo.org> on behalf of
Jordaan Fouche via qgis-za-user <qgis-za-user at lists.osgeo.org>
Sent: 21 March 2024 17:14
To: qgis-za-user at lists.osgeo.org <qgis-za-user at lists.osgeo.org>
Cc: j.fouche9 at gmail.com <j.fouche9 at gmail.com>
Subject: [QGIS-ZA-user] Coordinate conversion from Cape Datum Lo27? to EGS
84

Have a set of old borehole data that I wish to plot in QGIS.

They were clearly drilled pre 1994 (Hartebeesthoek) and I am really
struggling to plot them on QGIS. I suspect they may be Cape Datum.

The example that I am including is on the farm Rietvley 600 in the Balfour
district.

The coordinates are legible as X:2968350;Y: 40600.

Can somebody please help me.

Jordaan Fouche
Portion 11
Van Reenen Country Estate
Van Reenen
3372
Republic of South Africa

Tel: +27 (0)82 555 4227

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