how to get KeyPoint angle

asked 2016-09-11 04:53:32 -0600

santi
1

Hi anyone can help me ? I get a project to create a new keypoint, but only have the coordinates (x, y), then OpenCV have a KeyPoint class which have the following parameters:

pt (x,y) -> the position of the KeyPoints, size - size of the keypoint, angle - orientation of the keypoint, response - strength of the keypoint, octave - number of octave layer the keypoint is detected, class_id - the number of object the keypoint belongs to.

So how to get Keypoint angle, response and other parameters ?

I hope someone can help me. thank you ^_^

answered 2016-09-11 08:26:16 -0600

Tetragramm

7376 ●13 ●37

size is basically what it sounds like. How many pixels around the center do you use when calculating the keypoint? In some methods, this is variable.

angle is if you calculate an orientation. If you have a way of telling which way is "forward", for some consistent definition. This is often not used.

response is how strong your detector's belief that this is a keypoint is. So you can sort by strength. You should have something like this, even if it's just the FAST or corner response from earlier in your method.

octave is if you have multiple scales, which one is it found on? If you build a pyramid of images and search for keypoints on all of them, which one is this point from?

class_id: I don't know. I've never seen anything use this. I suppose if you have more than one distinct type you can put that here?

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I am not sure to understand what you mean by "a way of telling which way is "forward"".

So, just as an additional comment: the keypoint orientation is simply the orientation of the keypoint in the image (if you rotate the image by 20 deg). For example, some keypoints like SIFT are rotation invariant as you compute the descriptor after taking into account the orientation the keypoint.

class_id could be used for bag of words or could be used as a field left to the user for object recognition.

Eduardo ( 2016-09-12 04:20:28 -0600 )edit

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