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SynthEyes permits you to create constraints that limit the relative position between the two cameras in sophisticated ways, so that you can ask for specific relationships between the cameras, and eliminate unnecessary noise-induced chatter in the position.
If you work in an animation package and have a child object attached to a parent, you will have six numbers to adjust: 3 position numbers (X, Y, and Z), and 3 angles (for
example Pan, Tilt, and Roll, or Roll, Pitch, and Yaw). The same six numbers are used for the basic position and orientation of any object.
Those particular six numbers are not convenient for describing the relationship between the two cameras in a stereo pair, however! In the real world, there is only one real position measurement that can be made accurately, the inter-ocular distance, and it controls the scaling of everything.
Accordingly, SynthEyes uses spherical coordinates—which have only a single distance measurement—to describe the relationship between the cameras.
Of the two cameras, we’ll refer to one as the dominant camera (the one we want to think about the most, typically the right), and the other as the secondary camera. The camera parameters describe the relationship of the secondary (child) camera to the dominant (parent) camera. Which camera is dominant is controlled on the Stereo Geometry panel. In each case, when we talk about the position of a camera, we are talking about the position of its nodal point (inside the front of the lens), not of the base of the camera, which doesn’t matter.
You can think about the stereo parameters in the coordinate space of the dominant camera. The dominant camera has a “ground plane” consisting of its side vector, which flies out the right side from the nodal point, and its “look” vector, which flies forward from the nodal point towards what it is looking at. The camera also has an up vector, which points in the direction of the top of the camera image. All of these are relative to the camera body, so if you turn the camera upside down, the camera’s “up” vector is now pointing down!
Here are the camera parameters. They have been chosen to be as human- friendly as possible. Most of the time, you should be concerned mainly with the Distance and Vergence; SynthEyes will tell you what the other values are and they shouldn’t be messed with much.
Distance. The inter-ocular distance between the cameras. Note that this value is measured in the same units as the main 3-D workspace units. So if you want an overall scene to be measured in feet, the inter-ocular distance should be measured in feet as well. Centimeters is a reasonable overall choice.
Direction. This is the direction (angle) towards the nodal point of the secondary camera from the dominant camera, in the ground plane. If the secondary camera is directly next to the dominant camera, in the most usual configuration, the direction value is zero. The Direction angle increases if the secondary camera moves forward, so that at 90 degrees, the secondary camera is in front of the primary camera (ignoring relative elevation). See additional considerations in Two-Toe Revisited, below.
Elevation. This is the elevation angle (above the dominant camera’s ground plane). At zero, the secondary camera is on the dominant camera’s ground plane. At 90 degrees, the secondary camera is above the dominant camera, on its up axis.
Vergence. This is the total toe-in angle by which the two cameras point in towards each other. At zero, the look directions of the cameras are parallel, they are
converged at infinity. At 90 degrees, the look directions are at right angles. See Two- Toe Revisited below.
Tilt. At a tilt of zero, the secondary camera is looking in the same ground-plane as the dominant camera. At positive angles, the secondary camera is looking increasingly upwards, relative to the dominant camera. At a tilt of 90 degrees, the secondary camera is looking along the dominant camera’s Up axis, perpendicular to the dominant camera viewing direction (they aren’t looking at the same things at all!).
Roll. Relative roll of the secondary camera relative the dominant. At a roll angle of zero, the cameras are aren’t twisted with respect to one another at all; both camera look vectors point in the same direction. But as the roll angle increases, the secondary camera rolls counter-clockwise with respect to the dominant camera, as seen from the back.
You can experiment with the stereo parameters by opening a stereo shot, opening the Stereo Geometry panel, clicking More… and then one of the Live buttons. Adjusting the spinners will then cause the selected camera to update appropriately with respect to the other camera.
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