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November 15th, 2017, 01:19 AM  #1 
Newbie Joined: May 2017 From: London Posts: 2 Thanks: 0  How to combine 2 angles in 3D space
Hi folks, I have a bit of a problem and I can't seem to picture it in my mind or think of a way to draw it to help me solve it. I'm working in a editing/compositing piece of kit called Flame. In a 3D environment there is a camera which acts as the point of view and a flat finite surface with an axis attached. What I want to do is write an expression, which is like a formula or line of code, to turn the surface invisible when it rotated away from the camera. Now when the surface is directly in front of the camera I have done this by considering the x and y axis separately. So for x: Say the angle facing camera is 0. using a sine function I can get a +ve number from 90 to 90 and ve otherwise. I did the same for y. I reasoned that multiplying the 2 results would give a +ve or ve flag for the transparency. ie if you turned on the x axis 120 degrees (so away from camera) then the y 180 say, the 2 ves would make a +ve and you'd see the surface. Not sure how to denote this mathematically but it seems correct when I imagine it. This works perfectly when I build it too. I reasoned that z axis rotation makes no difference. By the way the axis rotates round with the surface rather than staying locked in space But then, when you start moving the surface in x and y it all falls apart and I can no longer picture the system. I think what I need to do is work out the angle from the surface to the camera point. So if you image holding a postit (my surface) 50cm in front of your face so the angle of the surface to your eye is 90 degrees. Now rotate the postit on its x and y axis. So far so good. But move the postit a distance to your left and up a bit. Rotate in x and y. Now, knowing all these values, how do you calculate the angle of the surface to your eye? if 90<theta<90 then it's visable. Otherwise it's transparent. Any ideas? Thanks 

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angles, combine, space 
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