how to find centroid, area, orientation of a particular region in an image

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If you have a mask over the region, you can convert it to a shape.

If the region in question is already a shape, you have jackpot-all those features are implemented to shapes. This article should be super useful for you. If in doubt, c++ is exactly the same, but different syntax.

Orientation can calculated from a fitted line. Be aware, that orientation is may trickier than first seems, look out for symmetries, and how you handle rotational errors.