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<DIV dir=ltr><FONT color=#000000 size=3 face="Times New Roman">Hello,</FONT></DIV>
<DIV dir=ltr><FONT color=#000000 size=3 face="Times New Roman">one of the libraries used by gvSIG (JTS) has a function called signedArea(). From their doc:</FONT></DIV>
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<DIV dir=ltr>"<FONT color=#000000 size=3 face="Times New Roman">public static double signedArea(Coordinate[] ring)</FONT></DIV>
<DIV dir=ltr><FONT color=#000000 size=3 face="Times New Roman">Returns the signed area for a ring.</FONT></DIV>
<DIV dir=ltr><FONT color=#000000 size=3 face="Times New Roman">The area is positive if the ring is oriented clockwise."</FONT></DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>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.</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>I understand Wolfgang is using polygons which were not previously edited with gvSIG, so maybe they are originally counter-clockwise?</DIV>
<DIV dir=ltr> </DIV>
<DIV dir=ltr>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...</DIV>
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<DIV dir=ltr><FONT color=#000000 size=3 face="Times New Roman"></FONT> </DIV>
<DIV dir=ltr>Regards,</DIV>
<DIV dir=ltr> </DIV></DIV>
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<DIV><FONT size=2 face="Courier New"><FONT size=3 face="Times New Roman">Juan Lucas Domínguez Rubio<BR></FONT>---</FONT></DIV>
<DIV><FONT size=2 face="Courier New"><FONT size=2 face="Courier New"><FONT size=2 face="Courier New">Prodevelop SL, Valencia (España)</FONT></DIV>
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<DIV><FONT size=2 face="Courier New">Tlf.: 96.351.06.12 -- Fax: 96.351.09.68<BR></FONT><A href="http://www.prodevelop.es/"><FONT size=2 face="Courier New">http://www.prodevelop.es</FONT></A><BR><FONT size=2 face="Courier New">---</FONT></DIV></FONT></DIV></FONT></DIV>
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<FONT size=2 face=Tahoma><B>De:</B> gvsig_internacional-bounces@listserv.gva.es en nombre de Wolfgang Qual<BR><B>Enviado el:</B> vie 27/11/2009 14:53<BR><B>Para:</B> Users and Developers mailing list<BR><B>Asunto:</B> [Gvsig_english] gvSIG 1.9::strange result when calculating area<BR></FONT><BR></DIV>
<DIV>Hi list,<BR>I just used the area()-Function to calculate the area of a polygon them and was surprised, as<BR>all values were negative. The absolute value was correct, "only" the minus is very strange.<BR>The layers I tested were from our official database. I am confused by this, as determinating the area using the <BR>measure tool results in the correct value (without "-"). Moreover, if I use the "split"-tool and recalculate the area,<BR>the area of the splitted geometries is positive (the rest remains negative). Very strange.<BR><BR>Any ideas are appreciated very much.<BR>Best,<BR>Wolfgang<BR><BR>
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