<html>
<head>
<meta content="text/html; charset=ISO-8859-1"
http-equiv="Content-Type">
</head>
<body text="#000000" bgcolor="#FFFFFF">
<div class="moz-cite-prefix"><font face="Times New Roman">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.<br>
<br>
Peter<br>
</font>
<pre class="moz-signature" cols="72">Peter Newmarch
Professional Land Surveyor
4Y GeoInformatics Pty Ltd
Tel : +27 31 5642856
Fax : +27 31 5643074
Mobile : +27 82 5705859
eMail : <a class="moz-txt-link-abbreviated" href="mailto:newmarch@land-surveyors.com">newmarch@land-surveyors.com</a> </pre>
On 2013/08/27 11:18 AM, Frank Sokolic wrote:<br>
</div>
<blockquote cite="mid:521C6ED6.8070306@worldonline.co.za"
type="cite">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?
<br>
<br>
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:
<br>
- use south-orientated coordinates for survey data
<br>
- use north-orientated coordinates for GIS data?
<br>
<br>
Frank.
<br>
<br>
On 26/08/2013 22:03, Gavin Fleming wrote:
<br>
<blockquote type="cite">Very topical point Frank
<br>
<br>
Now that EPSG and proj4 have codes and implementations for the
<br>
south-facing LO/Hartebeesthoek94 system, it's all well and good
except
<br>
as you say most GIS practitioners use north-facing, which we
should not
<br>
call 'LO' at all. I wish EPSG had set up the north facing series
instead.
<br>
<br>
If you get coordinates from a surveyor they are likely to be
<br>
south-facing, otherwise not, probably because GIS has not been
able to
<br>
handle south-facing till recently?
<br>
<br>
In my early GIS days if we got south-facing data, we'd flip it
to
<br>
north-facing manually before continuing.
<br>
<br>
There's a bit of a blocker in QGIS 1.9 at the moment where, if
you
<br>
define a north-facing LO CRS (which I prefer to call something
like
<br>
'SouthAfricaTM19' instead of 'LO19'), it forces '+axis=wsu' into
the
<br>
definition, which makes it south-facing. I've filed a bug report
[1]
<br>
about this, hoping it gets fixed before 2.0 is released.
<br>
<br>
I'm working in Lesotho now on parcel data which is in north
facing TM
<br>
(on the Cape datum still), though survey data comes in
south-facing. The
<br>
LO/Cape datum series is also in EPSG now, but also only as
south-facing
<br>
:-(.
<br>
<br>
[1] <a class="moz-txt-link-freetext" href="http://hub.qgis.org/issues/8487">http://hub.qgis.org/issues/8487</a>
<br>
<br>
Gavin
<br>
<br>
On 26/08/2013 17:08, Frank Sokolic wrote:
<br>
<blockquote type="cite">Dear List,
<br>
<br>
As many of you know, the South African coordinate reference
system is
<br>
defined as a south-orientated system, with Westings (Y)
increasing
<br>
towards the south and Southings (X) increasing towards the
West.
<br>
However, in a GIS context I've only ever seen SA CRSs (e.g.
Lo19,
<br>
Lo31, etc) represented with x-coordinates increasing eastwards
and
<br>
y-coordinates increasing northwards.
<br>
<br>
So, for example, the coordinates of the entrance to Durban
harbour are
<br>
represented in Hartebeesthoek94/Lo31 as
<br>
Y = -5641.000
<br>
X = +3305647.886
<br>
but in practice in a GIS this point is represented as
<br>
X = +5641.000
<br>
Y = -3305647.886
<br>
<br>
My question is: are there any GIS practitioners in South
Africa who
<br>
use the SA CRSs in the south-orientated sense?
<br>
<br>
Regards, Frank.
<br>
<br>
<br>
_______________________________________________
<br>
Africa mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Africa@lists.osgeo.org">Africa@lists.osgeo.org</a>
<br>
<a class="moz-txt-link-freetext" href="http://lists.osgeo.org/mailman/listinfo/africa">http://lists.osgeo.org/mailman/listinfo/africa</a>
<br>
</blockquote>
<br>
<br>
</blockquote>
<br>
_______________________________________________
<br>
Africa mailing list
<br>
<a class="moz-txt-link-abbreviated" href="mailto:Africa@lists.osgeo.org">Africa@lists.osgeo.org</a>
<br>
<a class="moz-txt-link-freetext" href="http://lists.osgeo.org/mailman/listinfo/africa">http://lists.osgeo.org/mailman/listinfo/africa</a>
<br>
<br>
</blockquote>
<br>
</body>
</html>