[gdal-dev] Area of hourglass shaped polygon

[Ramiro Gonzalez]

I use gdal to calculate the area of polygons drawn by a user over a map. The
points are added to the polygon in same order the user selects them. An
hourglass shaped polygon can be created adding 4 points like a 'z'.

When the polygon has the shape of an hourglass, the measure returned by
get_Area() is smaller than the sum of the areas of the two independent
triangles.
I'd like to know if there is a way to calculate the area in this situation?

I tried to intersect the polygon with another that contains it but the
operation fails when the polygon cross itself(return NULL). I could use this
to inform that the area calculated is invalid, but I'd like to know if there
is a better way of knowing this.

Thanks,
Ramiro
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