DangerPrediction

If it takes in account every single bullet in the air, then it is a form of [enemy] virtual bullets. Which does the same thing as waves, except in a more complicated way. It was the most used data structure, until someone had the insight of representing shots as circumferences growing in radius over time.

I use waves now, but also store a collection of headings inside the wave to cache k-NN search results. Combine a circumference and a heading and you have an exact x,y coordinate to use in danger estimation. Combine all circumferences with all headings and you have all x,y coordinates of enemy virtual bullets flying in the battlefield.

MN - thats pretty much exactly what I do. However, the interesting thing is what I do after I have the predicted x,y positions of bullets! :)