[OpenLayers-Dev] geodesic measures

Bart van den Eijnden (OSGIS) bartvde at osgis.nl
Tue Nov 11 16:10:10 EST 2008

Hey Tim,

great, the one thing I wonder here is if we should not have projection 
as a property of a geometry. It would make more sense to me that way 
than passing it as an argument to the getGeodesicXXX functions.

I think we had this discussion before but it was never concluded.


Best regards,

Tim Schaub wrote:
> Hey-
> A contributor (mwa at sourcepole.ch?) posted a patch for approximating 
> geodesic areas for polygons [1].
> I have used this algorithm to give geometries a getGeodesicArea method. 
>   In a similar way, I added a getGeodesicLength method using the 
> Vincenty algorithm already in Util.
> Combined, these give us handy methods for calculating metrics from our 
> geometries as if they were projected onto the earth's surface.  Both of 
> these calculations require that a projection is provided 
> (Geographic/WGS84 is assumed if none is given).
> This functionality allows a "geodesic" property to be added to the 
> measure control.  So, if your map projection is properly set, and if you 
> have provided the appropriate definition for that projection so a 
> transform to Geographic/WGS84 can be done, you can use the measure 
> control to do geodesic measures.
> All this is wrapped up in a new patch for ticket 1819 [2].  If anybody 
> cares to comment or test it out, that would be appreciated.
> Tim
> [1] http://trac.openlayers.org/attachment/ticket/1819/area_measurement.patch
> [2] http://trac.openlayers.org/ticket/1819

Bart van den Eijnden
OSGIS, Open Source GIS
bartvde at osgis.nl

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