problem with polyarea method, return NAN

Hi, I have multiple circles that intersect each other in the static area,I want to find union of them. I use polyarea method to find union,My problem is that this method sometimes return numerical result and sometimes return NAN result.What should I do to not get NAN as a result?

please Help me if you now my answer. Thanks.

[Mohammad Abouali]

Polyarea is to get the area of a polygon, Why do you use that to get the union area?

[fahimeh]

first,I use polybool to get the union,and after that I use polyarea to get numerical result.

Answer 1

[Image Analyst]

You might have to quantize/digitize them into an image, then AND them together. Use poly2mask to turn the vertices into images.

circleMask1 = poly2mask(x1,y1,rows,columns);
circleMask2 = poly2mask(x2,y2,rows,columns);
theUnion = circleMask1  & circleMask2;  % This is an image also.

[fahimeh]

How can I get the numerical result from the return of poly2mask?

[Image Analyst]

I have showed you. That's what circleMask1 and circleMask2 are.

[fahimeh]

Thank you very much,Your solution solve my problem.

Answer 2

[John D'Errico]

Note that the union of two polygons need not be a simple polygon. In fact, if the polygons are disjoint, then I'll bet that you get a result with a NaN in it. (I don't have the mapping toolbox that contains polybool, so I cannot test that statement.)

One solution is to discretize as Image Analyst has said, however, that will incur some loss due to the digitization into an image. Note that depending on the size of the numbers in your polygon, the digitization process may create a seriously huge image. So be careful!

A second solution is to catch the case when a NaN is returned, and then to perform the area computation as the sum of the two areas.

[fahimeh]

How much data loss by digitization?