Im having some problems with how to go about 3d line of sight. 2d line of sight is easy, you can use bresenham line with sine and cosine to form a line of sight arc... but how do i go about applying this to 3 dimensions?

Since noone has replied, I better share my thoughts at least...

Am I right that you are talking about 3D Line of Sight in 2D plane? or Are you on about 3D LoS in 3D? 2D one *can* be done without vector maths, so the two are pretty different. If 2D plane, is that flat 2D or isometric?

I don''t know about that "sin & cos arc" version of LoS. Sorry It sounds odd to me. Line of Sight is a "Line" precisely because it''s a straight line, whether it be a flat 2D plane or isometric plane (Or are you taking the earth''s curveture into consideration???). At least thats how I was brought up. I believe you use some different method. I think this is just an ignorance on my part.
When I use Bresenham for LoS, I start from starting (x,y) to the centre of the target''s (x,y). And check the pixels it passes through and see if it comes in contact with Obstruction cells.

I could give theoretical explanation on 3D LoS on 2D, but if you are on about something entirely different, then it''d be waste of time... so whether or not I can reply, I better wait till you reply