A Fast and Accurate Orthorectification Algorithm of Aerial Imagery Using Integer Arithmetic

In the past decade, imaging systems have increased in size and quality while decreasing in cost. As the cost has decreased, many aerial imaging applications have become practical such as tracking, vegetation indexing, coast line monitoring, etc. However, many of these applications require geo-location and orthorectification to enable analysis. Orthorectification is a computationally expensive process due to floating-point operations and divisions in the algorithm. To reduce the computational cost of on-board processing, two novel algorithm modifications are proposed. One modification is projection utilizing fixed-point arithmetic. Fixed-point arithmetic removes the floating-point operations and reduces the processing time by operating only on integers. The second modification is replacement of the division inherent in projection with a multiplication of the inverse. With these modifications, the processing time of the projection is reduced by a factor of 1.2 × with an average pixel position error of 0.5% of a pixel size for 128-bit integer processing and over 2 × with an average pixel position error of less than 15% of a pixel size for a 64-bit integer processing.