Question

This is basically just a math question.

Heres what I am having troubles with… I am having a difficult time coming up with how to phrase the question, so bear with me. Basically I think I need to use some advanced math to accomplish this, but I do not know what I need.

I will use some illustrations to make this clear. Spam prevention doesn’t let me post pictures… Here’s a simple concept image though: http://radleygh.com/images/gimp-2_2011-057-00-57-26-40.bmp

Objective: Determine if several objects lie within a cone on a 2D plane

Cone Properties:
Position (x, y)
Angle (0-359)
Spread (0-359, aka Width)
Distance (0++)

I can decide the brownish lines using a simple bit of math:

Angle_A = Angle + (Spread / 2)
Angle_B = Angle – (Spread / 2)
Angle_Target = Point_Direction(origin, object_position)

Now I thought of comparing these with the position of each object with a simple if/then statement:

If (Angle_A > Angle_Target) && (Angle_B < Angle_Target) Then Angle_Target is between A and B

This works… untill Angle_A or Angle_B pass the 0-360 threshold. 0* is between 45* and 315*… but the above if statement wouldn’t work. We can then determine which direction to check based on the size of the cone…

And what if the cone effect is larger than a 180* cone?

I’m not sure of the answer. I’m pretty sure I should be using Radians… But I do not understand the concept of Radians. if someone can point me in the right direction, perhaps show me an example somewhere, that would be wonderful!

I will continue to do my own research in the mean time.

Answer 1

You may consider a simple transformation which sets your coordinate system such that Angle_B is zero. In other words, instead of testing

Angle_B < Angle_Target < Angle_A

you may also use

0 < Angle_Target - Angle_B < Angle_A - Angle_B

If you apply a modulo 360° to all terms you’re logic should work:

0 < (Angle_Target - Angle_B) % 360 < (Angle_A - Angle_B) % 360