Calculating PPI

For each pixel in the image, the algorithm calculates on-demand PPI as follows:

1. Convert pixel coordinates to map coordinates.
2. Convert the map coordinates to Azimuthal Equidistant (AzEq) around the radar.
3. Calculate distance to radar (vector length) and azimuth angle to radar atan2.
4. Calculate the actual value at that point using a sweep parameter.