[Gdal-dev] Projected vs Geographic Coordinate Systems

Frank Warmerdam warmerdam at pobox.com
Mon Mar 19 23:57:44 EDT 2007

Simon Perkins wrote:
> Quick question: is it fair to say that most if not all georeferenced 
> raster images that one typically comes across use a projected (rather 
> than geographic) coordinate system?


I would agree that most geospatial image data is in a projected
rather than geographic coordinate system.  I'm not sure just how
overwhelming I'd claim this preponderance is.

> Do typical GIS packages handle rasters with geographic (latitude / 
> longitude) coordinate systems? And what do they do when displaying 
> rasters in a projected coordinate system together with, say, vector 
> layers in a geographic coordinate system? Is it usual to convert the 
> vector layer to the projected coordinates or vice versa?

It is more common to reproject the vector data to match the raster
data than to reproject the raster data to fit the vectors.

> Just wondering if I can get away with avoiding having to handle 
> geographic coordinate systems in my (mostly raster focused) application 
> for the time being... Any advice much appreciated!

I don't know your constraints or detailed objectives, but I'd be nervous
about making this simplication.  You could likely get away with treating
geographic coordinate systems similarly to projected coordinate systems.

Best regards,
I set the clouds in motion - turn up   | Frank Warmerdam, warmerdam at pobox.com
light and sound - activate the windows | http://pobox.com/~warmerdam
and watch the world go round - Rush    | President OSGeo, http://osgeo.org

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