[Gvsig_english] gvSIG 1.9::strange result when calculating area

[Juan Lucas Dominguez Rubio]

Hello,
one of the libraries used by gvSIG (JTS) has a function called signedArea(). From their doc:
 
"public static double signedArea(Coordinate[] ring)
Returns the signed area for a ring.
The area is positive if the ring is oriented clockwise."
 
It's not easy to check if this is the cause, because gvSIG changes the orientation when you add a counter-clockwise polygon in editing mode.
 
I understand Wolfgang is using polygons which were not previously edited with gvSIG, so maybe they are originally counter-clockwise?
 
I'm not sure this is a bug. You can get the area with "abs(area())" and the orientation with "area() > 0". Maybe the orientation is useful in some context...
 
 
Regards,
 
Juan Lucas Domínguez Rubio
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________________________________

De: gvsig_internacional-bounces at listserv.gva.es en nombre de Wolfgang Qual
Enviado el: vie 27/11/2009 14:53
Para: Users and Developers mailing list
Asunto: [Gvsig_english] gvSIG 1.9::strange result when calculating area


Hi list,
I just used the area()-Function to calculate the area of a polygon them and was surprised, as
all values were negative. The absolute value was correct, "only" the minus is very strange.
The layers I tested were from our official database. I am confused by this, as determinating the area using the 
measure tool results in the correct value (without "-"). Moreover, if I use the "split"-tool and recalculate the area,
the area of the splitted geometries is positive (the rest remains negative). Very strange.

Any ideas are appreciated very much.
Best,
Wolfgang


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