1. A method of coding feature location information of an image, comprising: generating a hexagonal grid, wherein the hexagonal grid includes a plurality of hexagonal cells; quantizing feature locations of an image using the hexagonal grid, wherein the quantizing feature locations comprises: for each feature location, generating transformed coordinates of the feature location from a two dimensional plane to a three dimensional space, rounding the transformed coordinates to corresponding nearest integers, and verifying the transformed coordinates belong to a hexagonal plane in the three dimensional space; generating a histogram to record occurrences of feature locations in each hexagonal cell; and encoding the histogram in accordance with the occurrences of feature locations in each hexagonal cell.