I am working on a simulation project that requires me to have entities walking around in a 3D world. I have all that working, matrix transformations, etc. I'm at the point where I need what is essentially a view frustum, so I can give each entity a visible area. However, when looking over the calculations required to do it, it seems like a perspective frustum is only required to be able to project it onto a 2D screen. Is there another, easier to code solution, that would function better, such as an orthogonal perspective? Could I just define a shape mathematically and test wether the coordinates of the objects are inside or out? I am not really a 3D coder (and I am doing this all from scratch, not using an engine or anything), so I would like the simplest solution possible for my needs.