Fast calculating feature point´s main orientation in SURF algorithm

In SURF algorithm, original process for feature point´s main orientation assignment is not optimized. It uses a sliding window covering an angle with 60 degrees shift around a circle region, and calculates the sums of all Haar responses to yield a vector in it. Along with the window rotating, many overlap regions generated. Therefore, a lot of responses summations need to be repeatedly taken. So the speed is slow. An algorithm for fast calculating feature point´s main orientation in SURF was proposed. It wiped off all repeated responses summations in the overlap regions, and all the Haar responses were just needed to be computed once, which not only decreased the complexity, but also increased the speed. Verified by the experimental results, the consuming time for our fast main orientation calculating algorithm is just 60% of the original one.