Precision high speed perspective transformation from range-azimuth

Abstract

A high speed and high precision coordinate transformation process for transforming image data in range-azimuth coordinates to horizontal-vertical display coordinates. The process is comprised of the following steps. Recursion initialization parameters and values for a perspective transformation are computed. Then, range and azimuth values using predetermined recursion equations are computed. A critical range factor using predetermined recursion equations and inverse operation is computed. Range and azimuth results are computed. Display address values are computed. Data is retrieved and the data is stored in display locations. A decision is then made whether the last display address has been stored. Additional display address values are computed until all addresses have been computed, and the process is ended once all addresses have been computed. The process is particularly suited for radar or lidar data, which is typically collected in B-scan format, and transforms the data into a virtual image on a head-up type display , which is in C-scan format. The process takes a display pixel in display coordinates and computes corresponding range and azimuth coordinates. The process uses a recursive form of a 2nd order Taylor series approximation, combined with a precise range calculation term in order to get the high precision and high speed performance. The use of the 2nd order Taylor series approximately allows the matrix calculations to be done at frame initialization for the first pixel and the subsequent pixel to pixel calculations to performed as an incremental addition to the initial values. The use of the recursive form of the approximation reduces the pixel incrementing calculations from nineteen operations per pixel to four operations per pixel. The precision range calculation requires four operations per pixel.