# Reflection symmetry

Hi there,

I am writing a project in C++ using opencv to implement an algorithm from a paper and one of the first step that I have to do is to take an image in input and find global dominant symmetry axis of the image using Reflection/Bilateral symmetry.

Here, in this image there are steps I have to do, to obtain the dominant symmetry axis:

I' ve already compute the first step, so I found SIFT keypoints and descriptor of image:

```
SiftFeatureDetector detector(0.05,5.0);
SiftDescriptorExtractor extractor(3.0);
std::vector<KeyPoint> keypoints;
detector.detect(img, keypoints);
Mat featureImg;
drawKeypoints(img, keypoints, featureImg, Scalar::all(-1), DrawMatchesFlags::DEFAULT );
imshow("Keypoints 1", featureImg);
Mat descriptor;
extractor.compute(img, keypoints, descriptor);
```

Now, I have to find (starting from available SIFT points) pairs of locally symmetric points using a threshold of symmetry magnitude but I'm finding a lot of trouble because there are no examples or ideas to start with.

Luckily, for the implementation of the next steps I am following a paper (page 4-5-6):

that describes mathematically the technique to determine the dominant symmetry axis and I decided to write to you to ask if it's the right way or if perhaps there is a simpler solution to my problem.

Thank you for your helps!

Simply said, if you do not provide more information, then how are you expecting people to help you? What are your own efforts? Which approach will you be taking? Having problems with something? A link to what this actually means? OpenCV doesn't provide this as standard function if you are wondering...

I'm sorry I was too brief but I really have little information. Now I've added more details to my problem and I hope that you help me. Thanks a lot!

I have no clue if it is the right approach. For that I would have to implement it myself and see if it works. I would say, you are on the right track, try programming this approach now and head back if actual errors pop up!