This paper proposes an ant colony optimization (ACO) based approach for point pattern matching (PPM) under affine
transformation. In the paper, the point sets matching problem is formulated as a mixed variable (binary and continuous)
optimization problem. The ACO is used to search for the optimal transformation parameters. There are two contributions
made in this paper. Firstly, we manage to modify the original ACO method by combining it with the leastsquares
method. Thus, it can handle with the continuous spatial mapping parameters searching. Secondly, we introduce a
threshold to correspondence finding, which rejects outliers and enhances veracity while using "Nearest Neighbors
Search". Experiments demonstrate the validity and robustness of the algorithm.