[OSGeo Africa] SACRS 'south-oriented' clarification

[Zoltan Szecsei]

Hi Gavin,

Your point 1 below
The only time I have ever seen TMSO as per "1d" below (ie: the actual 
numeric columns of a coordinate list swopped) is in the early days of 
ReGIS .
This caused havoc, and I presumed that the reason the ReGIS guys did it, 
was a confusion of the Survey coordinate naming convention.

To put it in the simplest terms:
Cartesian 'okes called it XY and survey 'okes call it YX - but in a 
coordinate list format, the 1st column is East/West, and the second 
column is North/South - regardless of whether that column is called X or Y.

Point 2 - no idea what form ArcGIS uses

Point 3 - Surveyor conventions:
It would be better to simply look at the coordinate lists printed on any 
SG General Plan or Diagram.
Such coordinates from a surveyor, in electronic form, might already have 
been altered to suit some software package.
The coordinates printed on a survey diagram are the definitive ways 
surveyors use their coordinates. ie:

Name
	Y
	X
A
	0.0000000003128453 	3098441.7473872434347868

	
	


(without as many decimal places)

As you can see: 1st column for "left-right" value, and second column for 
"up-down" value.

Hope this helps, and that my point of view is correct.

Regards,
Zol



On 2013/09/03 14:16, Gavin Fleming wrote:
> Hi all
>
> We are adding some predefined north-oriented SACRS definitions to QGIS 
> so that we can all easily use the normal "LO" GIS data and not have to 
> 'roll our own' custom CRS definitions, which should make everyone's 
> lives easier.
>
> The proj4 South-oriented (TMSO) definitions from the EPSG that are in 
> QGIS 2 (all the 'Lo' Hartebeesthoek and Cape ones) are correct 
> according to the EPSG but I would like to establish whether everyone 
> follows the EPSG axis-order convention in South Africa. If the norm is 
> to NOT follow the axis order conventions, then the proj4 definitions 
> need to be altered.
>
> 1. Look at the alternatives for the point below. Say whether you 
> consider c or d to represent how you obtain and use TMSO coordinates:
>
> a. Here is a WKT point in EPSG:4326
>
> POINT(23 -28)    Axis order is x,y
>
> b. This is the same point in what we GIS users in SA would call 
> colloquially 'LO23' (i.e. north facing SACRS)
>
> POINT(-0.0000000003128453 -3098441.7473872434347868)   Axis order is x,y
>
> c. This is the same point in EPSG:2050 (SACRS) with EPSG axis-order 
> convention (y,x)
>
> POINT(0.0000000003128453 3098441.7473872434347868)   Axis order is y,x
>
> d. This is the same point in EPSG:2050 (SACRS) with what I think is 
> South African axis-order convention (x,y)
>
> POINT(3098441.7473872434347868 0.0000000003128453)   Axis order is x,y
>
> 2. Can anyone tell me what axis order ArcGIS expects TMSO coordinates 
> to be in?
>
> 3. Please send a small sample of data that you *know* is in TMSO. e.g. 
> some raw land surveyors data.
>
> If you've read this far I'd be grateful for a quick response to 1, 2 
> and 3.
>


-- 

===========================================
Zoltan Szecsei PrGISc [PGP0031]
Geograph (Pty) Ltd.
P.O. Box 7, Muizenberg 7950, South Africa.

65 Main Road, Muizenberg 7945
Western Cape, South Africa.

34° 6'16.35"S 18°28'5.62"E

Tel: +27-21-7884897  Mobile: +27-83-6004028
Fax: +27-86-6115323     www.geograph.co.za
===========================================

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