[OSGeo Africa] Using south-orientated CRSs for GIS in SouthAfrica
Michael D Manyama
phalageospatial at gmail.com
Wed Aug 28 00:07:16 PDT 2013
Thanks Aslam, it all makes sense now, atleast just from the naming
convention.
Regards,
Michael D Manyama
Chief Executive Officer
Phala Geo-Spatial Solutions
206 Blue Berry Complex,Faire Glen,Pta
084 710 8815
086 611 4538
phalageospatial at gmail.com
mike.dudu.manyama
"We must overcome the notion that we are ordinary, it robs you of the chance
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-------Original Message-------
From: Aslam Parker
Date: 8/27/2013 12:54:31 PM
To: africa at lists.osgeo.org; newmarch at land-surveyors.com
Subject: Re: [OSGeo Africa] Using south-orientated CRSs for GIS in
SouthAfrica
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
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>>> 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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