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

Fri Aug 30 02:02:00 PDT 2013

This is all very interesting.

I have been working for SADC in vulnerability, poverty and food insecurity assessment and mapping is a key part of the work. Mostly, we work at national level and dealing with the different standards for each of the member states is a head ache. In SADC's mandate, they must "Standardise" and "Harmonise" national systems, so wouldn't it be nice if this could be done with map projections. In our work, we very often need densities spread over the national (or for big countries in the region--provincial) level, and then we also often need distances.

My question to Aslam is: is there any kind of agreed standard for national-level maps, as opposed to the larger-scale Topo Maps? UTM works fine for Lesotho, Swaziland and Malawi because they are all so narrow but I am wondering about the rest? Has anything been proposed or set forth in any way? I can't find anything in SADC. Most of the data is stored in Long-Lat which is fine for storage but needs to be reprojected for our analysis work (but not all the way down to 1 deg--we need to work from 6 deg up to 20 deg).

Can we propose a set of Albers EAs and Lamberts CCs (such as the 1:500000 standard) to cover the SADC region country by country for analysts to work with? Can these be standardised? How interested is the NGI in helping with the possibility of a regional standard? My goal here is to use QGIS and open source software to get vulnerability practitioners (and indeed a great many other practitioners in other fields, too) in all member states all working on maps, instead of maps only being done by a few geeks in a office hidden away in a government building somewhere.

All the best,

Charles Rethman

On 29 Aug 2013, at 9:19 AM, Frank Sokolic <sokolic at worldonline.co.za> wrote:

> Hi list users,
> 
> Here's a slightly tongue-in-cheek article discussing the south-orientated CRS we use in southern Africa:
> http://trac.osgeo.org/proj/wiki/TMSO
> 
> Frank.
> 
> On 28/08/2013 09:29, Aslam Parker wrote:
>> Hi All
>> The SA coordinate system uses the Transverse Mercator Projection (which
>> is standard in all GIS software) and applied certain rules to it (such
>> as south orientation). There is no reason why you cannot set a project
>> up in SA system (south oriented) and import whatever vector projection
>> you like, be it UTM, standard TM, as long as you associate the correct
>> coordinate system with the imported data, everything should fall in the
>> correct space.
>> 
>> 
>> >>> Frank Sokolic <sokolic at worldonline.co.za> 8/27/2013 2:07 PM >>>
>> Hi Aslam,
>> 
>> What is NGI's position on GIS data? When I've obtained GIS data from NGI
>> in the past it has always been supplied as north-oriented, and not in
>> the south-oriented SA CRS. Was this because in the past there weren't
>> any GIS packages that supported the south-oriented SACRS?
>> 
>> Now that GIS programs are starting to support the SACRS (e.g. QGIS 2.0,
>> ArcGIS) does this mean that NGI will start distributing GIS data in the
>> correct orientation?
>> 
>> Frank.
>> 
>> 
>> On 27/08/2013 12:46, Aslam Parker wrote:
>> > 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
>> > <http://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
>> <mailto:aparker at ruraldevelopment.gov.za>__
>> >
>> > __
>> >
>> > __
>> >
>> > PPlease 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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>> >>>
>> >>>
>> >>
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