Frank Warmerdam warmerdam at pobox.com
Thu Jun 21 08:43:16 EDT 2001

Paul Selormey wrote:
> Hello All,
> This is very basic question, but please bear with me. I have bought two
> books
> on projections so far and still could not find any information on it.
> What is the WGS-1984? and what is its importance with regards to
> projections?


There is a datum, and an ellipsoid of this name.  I am not properly trained
in these matters, but the ellipsoid is the shape of the earth, normally
expressed as a major and minor axis, and a datum is a model of various earth
irregularities and survey errors. 

WGS84 is a common ellipsoid/datum.  For use with PROJ.4 you would use
this to set the +ellps or +datum parameters after having defined all your
other projection parameters.  

The material at the following URL seems like a good overview of datum issues.


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    | Geospatial Programmer for Rent
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