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

Sun Sep 1 06:56:41 PDT 2013

Hi All

I've picked up two major issues in the past couple of weeks with proj4 
and QGIS 1.9 that make it impossible to work with the official TMSO 
SACRS for the moment.

I've also put together some CRS codes and suggestions for working with 
southern African data.

The CRS notes and references to the bugs are in a public gist at 
https://gist.github.com/gubuntu/6403425 that I hope we can maintain as a 
common resource.

Frank, I've only ever got longlat vector data from NGI but I guess if 
they ever distributed it in TM coords they should be south-oriented. NGI 
orthophotos are indeed distributed in north-oriented TM, not SACRS.

Gavin

On 27/08/2013 14:07, Frank Sokolic wrote:
> 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
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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.
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> Africa mailing list
>>>>> Africa at lists.osgeo.org
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>>>>
>>>>
>>>
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>>
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-- 
regards

Gavin

Gavin Fleming
http://afrispatial.co.za
t: 0218620670
c: 0845965680
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