[postgis-users] different results for area with different programms

[Sandro Santilli]

On Thu, Feb 23, 2012 at 02:58:49PM -0000, Astrid Emde wrote:
> Hello,
> 
> I calculate the area of polygons and get different results with diffrent
> programms.
> 
> Here is an example polygon:
> 
> Select st_area(geometryfromtext(
> 'POLYGON ((
>   2569220.83 5630370.607,
>   2569215.357 5630374.968,
>   2569216.017 5630375.795,
>   2569216.19 5630376.01,
>   2569221.663 5630371.649,
>   2569220.83 5630370.607
> ))',31466) );
> 
> These are the results that I get:
> * PostGIS: 9.337890625 (with "POSTGIS="1.5.1" GEOS="3.2.0-CAPI-1.6.0")
> * AutoCAD Map 2012: 9.3362
> * Kanal++ [1]: 9.3361645
> 
> PostGIS gives back a slightly bigger area than the other programms. Do you
> know why and who is right?

PostGIS area calculator improved in 1.5.4 (yet to be released).
BTW, are those meters ? You're worried of 0.001 square meters precision ?
What's the precision of your coordinates ? Are your straight lines
in your model really straight in the phisical world ?

--strk;

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