I've been having some trouble coming up with a generic formula for figuring out the closest interception point between two travelling objects, and I'd appreciate any help on this.

Here's the context:

- Object A will travel at a defined constant speed and angle. Object B does not have a defined angle, only speed:

- Object B is perpendicularly distant to object A's path by a certain amount. The intersection of B's perpendicular distance to A's path gives point P:

- Object B will move at a certain angle, calculated with the formula, as such to intercept A with the shortest travel possible:

- When both objects start to move (A with its predefined speed and angle, B with its predefined speed and calculated angle), they will meet at a specific point, taking as little time as possible for this:

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Note there are a couple of cases where B will not intercept A:

- When B is positioned "ahead" of A in A's path (like in these diagrams), if B takes more time than A to reach point P then B can never intercept A (since B can't even reach A by the shortest distance possible, which would be the perpendicular distance).

- When B is positioned behind A in A's path, if B's speed is equal to or less than A's then B can never reach A (they'll either move by the same amount and never get closer, or A will only gain on B).

I have an early-out test for these, so proceeding to calculate the angle\point of interception is the difficulty!

So far I had something that used the time B took to reach P, and how far A travelled along this time. A's travel subtracted from the distance from A-to-P gives a sort of B's "advantage" distance over A. We know that the point of closest interception we want to calculate lies between this segment, until point P.

I also tried (fruitlessly) to model the tangent transformation of segment BP so as to figure out which angle segment BP needs to be transformed by to become a segment that intersects A's path, and that B takes the same amount of time to travel this segment as does A to get to the point of intersection:

In the above example, B should cover distance BI as fast as A covers distance AI. By "as fast" I mean, "in as many logic cycles as"; there's no unit of time. Both objects move by their speeds and angles at every logic cycle.

**Edited by Kryzon, 03 November 2012 - 02:47 PM.**