January 14th, 2012, 08:39 AM  #1 
Newbie Joined: Jan 2012 Posts: 6 Thanks: 0  Geometry Issues!
Hi, I'm working on the interface for a computer game (nothing too complicated) but it requires me to manipulate a 3D Cartesian coordinate system as well as a camera that is using a polar coordinate system for positioning. I have it all working except for one thing. The Setup: I can easily do a translation in 3D cartesian space (add x,y,z to a set of points to move them in a direction) then do a simple rotation around the Z axis (for azimuth) and then rotating around the X axis (for elevation). The Problem: Now, the user clicks on his screen again and drags it to translate the coordinates a second time (user's screen is still showing the coordinates as they are rotated). Basically all I have to do is do a reverse rotation on my new "coordinates" so that they translate correctly as the user is seeing. ...And my brain is fizzling. I've been staring at this for 5 hours. It's simple logic but I'm failing. Can anybody give me a hand here? Please >.< 
January 14th, 2012, 10:01 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 21,105 Thanks: 2324 
Whatever "it" is gets moved to some point  why does it matter whether it got there by one translation or two? If, say, the camera has to move for some reason, surely all that's needed is the new position, no matter how many translations were done.

January 14th, 2012, 10:27 AM  #3 
Newbie Joined: Jan 2012 Posts: 6 Thanks: 0  Re: Geometry Issues!
If I click on the screen and drag it, then rotate by x degrees azimuth and y degrees elevation, then click and drag again, my first translation was done at perspective 1. My second was done at perspective 2. I need a simple way to "undo" the perspective change in reference to the translation because I'm measuring my coordinates without reference to the perspective shift. Another way to put it. If I have a camera mounted on a robotic arm that's pointed down at a sphere from above, then I move the focal point of the camera 10 units down (y = 10) now I change the camera's position by X degrees (azimuth) and Y degrees (elevation). Now I move the camera's focal point 10 units down (referenced by my current view). ...What equation tells me how I moved the camera with reference to the original view? ( X degrees azimuth and  Y degrees elevation). ...I've been trying it and I'm doing something seriously wrong. 
January 19th, 2012, 01:39 PM  #4 
Global Moderator Joined: Dec 2006 Posts: 21,105 Thanks: 2324 
Would it be easy if you used only Cartesian coordinates? If so, why not do so?


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