[OSGeo Africa] EPSG 205x

Tue Jul 21 10:04:27 EDT 2009

Hi Graeme

Thanks for the response. Yes, I am well aware of the resource available
through spatialreference. This is where my confusion comes in. if you run
the following:

cs2cs +proj=latlong +datum=WGS84 +to +proj=tmerc +lon_0=31 +datum=WGS84 

and then enter:
30.352 -29.623

You will get:
-62758.77       -3278498.65 0.00

This is of course the correct answer. Which immediately tells me that the
definitions in place can handle our projection systems, and it is merely a
factor of syntax. Please correct me if I am wrong.

Andrew

-----Original Message-----
From: africa-bounces at lists.osgeo.org [mailto:africa-bounces at lists.osgeo.org]
On Behalf Of Graeme McFerren
Sent: 21 July 2009 03:26 PM
To: 'Africa local chapter discussions'
Subject: RE: [OSGeo Africa] EPSG 205x

Hi Andrew

This question needs a bit of disambiguation (oops, I sound like
wikipedia...) and discussion

I remind you btw of the excellent resource www.spatialreference.org

The Hartebeesthoek94 coord system is EPSG:4148
(http://www.spatialreference.org/ref/epsg/4148/ ) defined in proj format as:
+proj=longlat +ellps=WGS84 +towgs84=0,0,0,0,0,0,0 +no_defs 

Projected systems can of course be based on this, but if you are
specifically after the LO flavour of things check out:

http://www.spatialreference.org/ref/epsg/2046/
http://www.spatialreference.org/ref/epsg/2047/
...
http://www.spatialreference.org/ref/epsg/2055/

None of these provide a proj4 definition though, nor can I find one in
PostGIS or via OSR, implying to me that it would be difficult to project
into these projections if using some FOSS Tools. 

I don't think your proj4 style attempt will quite work though, because it
does not provide for the necessary southward orientation. LO is a
south-oriented Transverse Mercator AFAIK

When resolved, this should be contributed to SpatialReference.org, I think

Regards
Graeme

>>> "Andrew de Klerk" <andrew at quartex.co.za> 07/21/09 2:30 PM >>> 
Jeff - It has already asked on this list. I am yet to get a conclusive
definition of what it is from about three different lists. 

I guess it is not as clear cut as it seems. I would have also thought that
with the Quantum training session the other day, we would have our own proj4
definitions sorted out. No?

Andrew

-----Original Message-----
From: africa-bounces at lists.osgeo.org [mailto:africa-bounces at lists.osgeo.org]
On Behalf Of Jeff McKenna
Sent: 21 July 2009 02:08 PM
To: Africa local chapter discussions
Subject: Re: [OSGeo Africa] EPSG 205x

Andrew de Klerk wrote:
> Hi
> 
>  
> 
> Can anyone confirm what the correct Proj4 definition is for our 
> Hartebeesthoek projections. The closest I have come up with is (for 2054):
> 
> +proj=tmerc +ellips=WGS84 +datum=WGS84 +lon_0=31 +k_0=1 +units=m +no_defs
> 
>  
> 
> I have tried on numerous occasions to get someone in the know to say if 
> its wrong or right. I do not know enough about the inner workings of 
> projection systems nor the different options available in the proj4 
> definitions - so if anyone who knows more than me about either of these 
> can help me/us come up with a definite definition this would help.
> 
>  
> 
> Gavin - I know you were looking into this a while ago? Did you get any 
> further?
> 
>  
> 
> Thanks
> 
> Andrew

Andrew,

Maybe you should ask this question on the Proj mailing list 
(http://lists.maptools.org/mailman/listinfo/proj), I bet that is where 
you'll find help.

-jeff

-- 
Jeff McKenna
FOSS4G Consulting and Training Services
http://www.gatewaygeomatics.com/

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