3d viewing illustrated. what you see depends on your position in the real world, what you see...
TRANSCRIPT
3D VIEWING ILLUSTRATED
WHAT YOU SEE DEPENDS ON YOUR POSITION
• In the real world, what you see depends on where you stand, the direction you look, how you tilt your head, and so on.
3D VERSUS 2D
• In 3D, the y-axis typically points up instead of down. • Negative coordinates, which are rarely used in
2D, are quite common in 3D. • Because of this, the origin is at the center of
space as opposed to the top-left corner as in 2D
MAJOR DIFFERENCES BETWEEN 2D AND 3D
RIGHT HANDED COORDINATE SYSTEM
CAMERA POSITION
• Camera positioned at (5, 5, 5):• Looking at the southeast side
SOUTHWEST SIDE
• Move the camera to position (-5,5,5):• Looking at the southwest side
LOOKDIRECTION
• The lookdirection is a vector that tells the camera where to look.• For the camera below the lookdirection is (-1,-1,-
1):
MOVING THE CAMERA
• Moving the camera does not change the lookdirection:
THE LOOKDIRECTION IS BASED ON A LOOKAT POINT
• Changing the lookdirection:
LOOKAT AND LOKDIRECTION
• The easiest way to determine the lookdirection is specify a lookat point in the scene and subtract the camera position from it:
lookat – camera position• For the above camera position, if the lookat is
(0,0,0), then look direction is:• Lookdirection = (0,0,0) – (-5,5,5) = (5, -5, -5)
SOUTHWEST VIEW
• Given an orthographic camera and the above lookdirection we get the following scene:
THE UP DIRECTION
• The lookdirection is not enough to get the correct view:
UP DIRECTION NOT CHANGED
UP DIRECTION WRONG
CORRECT
CORRECT
TRANSFORM UP DIRECTION
UP DIRECTION ANALOGY
if you're designing a flight simulator, up is the direction perpendicular to the plane's wings, from the plane toward the sky when the plane is on the ground.
DEFAULT CAMERA POSITION
ROTATING THE CAMERA
• We will call rotation around the look vector (or z axis) Roll. • Rotation around the up vector (or y axis) is called
Yaw. • Rotation around the Right vector (x axis) is called
Pitch. • Below is a picture of an aircraft showing roll, pitch
and yaw in terms of the aircraft's local axis. Note: we can use a similar system for our object rotations
ROLL, PITCH AND YAW