[OSGeo Africa] South Africa Aerial Imagery

[Grant Slater]

On 7 January 2013 20:37, Hanlie Pretorius <hanlie.pretorius at gmail.com> wrote:
>
> Thanks for setting this up, it's great.
>

Pleasure. I had fun setting it up.

> I've managed to load it as a raster layer in QGIS 1.8.0 in Windows, using
> the XML file you provided.
>
> I then read up a bit about the projection it uses and was a bit concerned
> that it's a 'whole world' projection with 0 deg, 0 deg as the centre, and
> according to spatialreference.org. errors of up to 800m  in position may
> occur.
>
> So I loaded some vector layers in WGS84 CRS from the census on top of the
> images and the parts of Cape Town that I checked seemed fine. Boundaries ran
> nicely along centres of roads etc.
>
> Have you perhaps checked other parts of the country for errors because of
> the projection, or is this a silly question?
>

I have been using the imagery thorough South Africa, positional
accuracy seem to be good. South Africa is far away enough from the
poles ;-)
The choice of using EPSG:3857 was a pragmatic decision to ensure
compatibility with Google Maps, Bing Maps, OpenStreetMap etc, as they
also use EPSG:3857 for their map image tiles.

Regards
 Grant