[OSGeo Africa] Using south-orientated CRSs for GIS in South Africa
newmarch at land-surveyors.com
Tue Aug 27 02:42:24 PDT 2013
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.
Professional Land Surveyor
4Y GeoInformatics Pty Ltd
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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?
> 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
>> 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 
>> 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
>>  http://hub.qgis.org/issues/8487
>> 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.
>>> Africa mailing list
>>> Africa at lists.osgeo.org
> Africa mailing list
> Africa at lists.osgeo.org
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