The Interactive Geometry Software Cinderella

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Forums->Cinderella Support (E)->Area of a polygon -- getting a negative value.

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Area of a polygon -- getting a negative value.

I decided to attempt to get an approximation of the area of two partially overlapping circles by created a polygon that approximates the borderline of the two overlapping circles. Briefly assuming "O" is a circle then overlap another O only partially ... leaves a shape similar to this ((X)) and where X is the area I want to calculate.

So, I created a polygon with 12 points on a grid that approximates this.

And then used "MEASURE AREA" to get the area of the polygon...
But it gives me a NEGATIVE area.

When I tested it using a simple square made of 4 segments the area is positive.
I did notice that once the polygon for a square was created I could move a point from say upper left to the mirror position and it would create a negative value.

I suppose it might be useful to have a setting that forces only positive/negative/any sign values for a given polygon (or any shape...boundary in the future)

I could post the example... if you want to look at it?
If so, where should I send it too?

on: Wed 08 of Mar, 2006 [19:47 UTC] reads: 148583

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author message
Aw: Area of a polygon -- getting a negative value.
on: Thu 09 of Mar, 2006 [06:58 UTC]
Orientation of the polygon matters in Cinderella. See Area in the manual.


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