[OSGeo Africa] Using south-orientated CRSs for GIS in South Africa

Tue Aug 27 03:46:30 PDT 2013

Hi All

Can we please not call it the Lo system, it is the South African
Coordinate Reference System. For a detailed and authoratative definition
and explanation, please download 
http://www.eepublishers.co.za/images/upload/positionit_2012/SA%20Coordinate%20reference%20system%20part1+2.pdf

Apparently ESRI has recently  implemented the south oriented SACRS in
their software.

Aslam Parker | Director: Geo-spatial Information and Professional
Support
|Chief Directorate: National Geo-spatial Information www.ngi.gov.za|
Cape Town|
Tel +27 21 658 4302| Fax +27 86 211 7919| Mobile 082 331 8501|
aparker at ruraldevelopment.gov.za 

P Please consider the environment before printing this email and/or any
related attachments>>> Peter Newmarch <newmarch at land-surveyors.com>
8/27/2013 11:42 AM >>>
If one is producing maps in a country, then its common practice to use
the national mapping system of that country. So I guess NGI does have a
policy in the sense that their is a national mapping system for all data
- which is the current Lo system.

Peter
Peter Newmarch
Professional Land Surveyor
4Y GeoInformatics Pty Ltd
Tel       : +27 31 5642856
Fax       : +27 31 5643074
Mobile    : +27 82 5705859
eMail     : newmarch at land-surveyors.com On 2013/08/27 11:18 AM, Frank
Sokolic wrote:

ArcGIS 10+ and the soon-to-be-released QGIS 2.0 contain the (correct)
south-orientated definitions of the Lo coordinate reference systems.
However, the problem with this is that there is a HUGE amount of spatial
data in SA and neighbouring countries that use a "north-facing"
orientation. To convert all of this to the south-orientated system will
have a massive impact on the GIS community both in terms of money and
time. Can we afford this? 

Does National Geo-spatial Information (NGI) have a policy on which CRS
to use for GIS? They also supply spatial data using "north-orientated"
coordinates so perhaps they have a policy somewhere that states: 
- use south-orientated coordinates for survey data 
- use north-orientated coordinates for GIS data? 

Frank. 

On 26/08/2013 22:03, Gavin Fleming wrote: 

Very topical point Frank 

Now that EPSG and proj4 have codes and implementations for the 
south-facing LO/Hartebeesthoek94 system, it's all well and good except

as you say most GIS practitioners use north-facing, which we should not

call 'LO' at all. I wish EPSG had set up the north facing series
instead. 

If you get coordinates from a surveyor they are likely to be 
south-facing, otherwise not, probably because GIS has not been able to

handle south-facing till recently? 

In my early GIS days if we got south-facing data, we'd flip it to 
north-facing manually before continuing. 

There's a bit of a blocker in QGIS 1.9 at the moment where, if you 
define a north-facing LO CRS (which I prefer to call something like 
'SouthAfricaTM19' instead of 'LO19'), it forces '+axis=wsu' into the 
definition, which makes it south-facing. I've filed a bug report [1] 
about this, hoping it gets fixed before 2.0 is released. 

I'm working in Lesotho now on parcel data which is in north facing TM 
(on the Cape datum still), though survey data comes in south-facing.
The 
LO/Cape datum series is also in EPSG now, but also only as south-facing

:-(. 

[1] http://hub.qgis.org/issues/8487 

Gavin 

On 26/08/2013 17:08, Frank Sokolic wrote: 

Dear List, 

As many of you know, the South African coordinate reference system is 
defined as a south-orientated system, with Westings (Y) increasing 
towards the south and Southings (X) increasing towards the West. 
However, in a GIS context I've only ever seen SA CRSs (e.g. Lo19, 
Lo31, etc) represented with x-coordinates increasing eastwards and 
y-coordinates increasing northwards. 

So, for example, the coordinates of the entrance to Durban harbour are

represented in Hartebeesthoek94/Lo31 as 
Y = -5641.000 
X = +3305647.886 
but in practice in a GIS this point is represented as 
X = +5641.000 
Y = -3305647.886 

My question is: are there any GIS practitioners in South Africa who 
use the SA CRSs in the south-orientated sense? 

Regards, Frank. 

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