[OSGeo Africa] Using south-orientated CRSs for GIS in South Africa
gavinjfleming at gmail.com
Mon Aug 26 13:03:10 PDT 2013
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 
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 :-(.
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
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