Large Scale Filtering

In their paper on the Growth and Decay Storm Tracker, Wolfson et al. (1999) described the large scale filtering technique in some detail. The filtering process, which is applied to any gridded weather radar data field, is as follows:

1. The center point of the two-dimensional filter (which is an ellipse rotated in 10-degree increments, see Figure 1) is placed over each point in the data field to be filtered. The average of all the image points that lie under cross-hatched pixels in the filter (see Figure 1) is computed.
2. The filter is then rotated by 10 degrees (through $180^o$) and the average value with this filter orientation is recomputed.
3. The maximum of the average values obtained at each of the filter orientations is set as the filtered value at that data point.
4. Steps 1-3 are repeated for every pixel in the image.

This paper describes an equivalent implementation of the above process and describes how that implementation can be made faster.