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From: Rebecca on 1 Jun 2010 10:32
I am using regionprops to attempt to identify shapes in an image. Using the extent feature, I am able to make a fairly accurate guess of a shape, however, this is not foolproof. I would like to also use other geometric features of shapes to make sure that the image is identified correctly. I tried using the area property, since each shape has a distinct area. For example, using (1/2)*MajorAxisLength*MinorAxisLength = area for a triangle. The problem is, even for shapes that I know are triangles, this equation does not work out for the area in regionprops or using bwarea().
From: ImageAnalyst on 1 Jun 2010 11:48
You may have to use several of the measurements, or even combinations
of them like the circularity = (4*pi*area)/Perimeter^2 to uniquely
identify several different shape types (e.g. circle, triangle,
rectange, etc.). The more shapes you have the more likely it is that
you'll need more parameters to describe it. regionprops defines major
and minor axis length for a triangle not in the way that you think.
It fits an ellipse to the blob. So it won't be what you expect for a
triangle which would be the length of one of the sides and the
distance from that side to the other, third vertex. That's why it
fails for you and your equation.
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