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Why there is no Circle in a geographic feature
Posted by: Ulf Küßner
Date: May 09, 2007 03:28PM


You may have found that there is no circle in the Open Gis specification.
Now, a circle - such a basic shape - should be referenced, should it not?

Well - it should not, basically because it's not possible to draw a consistant circle onto a projected earth's surface.
Now, I'm sure you can pull the trick, and draw a circle onto earths surface - but what would happen is you project it onto a map - it wouldn't be a circle anymore, more some ellipse, maybe even a heart shaped feature. So what good would it do to define a circle feature that won't be a circle?
In fact - Circles are Point features, with a circular Symbol attached - this would make sure that a circle is always represented as a circle on a map - however, it won't always cover the same area.

One might argue that it would make sense to define a circle in a given projection only, say in a geographic coord system, that can easiely represent a circlular feature on the earth surface, say a radar range scope. That would be possible, but not portable. as such, it is left to application logic to turn a circle into a polygon, whose points can easiely be projected in a lossless manner.


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Written By
April 11, 2007 03:39AM
May 08, 2007 12:32AM
Why there is no Circle in a geographic feature
May 09, 2007 03:28PM

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