[OSGeo Africa] Using south-orientated CRSs for GIS in South Africa
Frank Sokolic
sokolic at worldonline.co.za
Thu Aug 29 00:19:34 PDT 2013
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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