Basic considerations:

• The camera, describing VIOSO native coordinate system
  • By positioning the test image and entering the radius and start angle, you name a 3D coordinate for every projector pixel on screen.
  • This is like a measured point with some tolerance in the real world.
  • View poses must use the same eye point.
• A main view direction and eye point, describing the correspondence between IG and VIOSO
  • All views have same eye point.
  • There is no fix eye in IG — the eye can be everywhere in the virtual world.
  • There is a main view direction. This is where we go “forward”.
  • So every view is just an angular offset (yaw, pitch, roll angle) to that main view.
• Offset angles to a main view
  • IG’s forward.
  • View from eye “forward” to screen.
  • Starting at SPCalibrator 4.3, it became easier, as we can use relative angles now.

To position a camera somewhere else, here is the workflow on how to position a fisheye camera at 2m height on a 4m diameter / 3m height cropped dome (220°x120°) screen.

• Use HQ calibration kit. It comes with a 185° lens and very sensitive sensor
  • Fix your camera at 2m height facing the screen.
  • The central ray must go through the center of the imaginary sphere that the screen is part of.
  • Go as far back as you need to see your whole screen. If the upper left/right corner does not have any projection on it, you may need to move closer.
  • Adjust “Dome master” test image:
    • Pole is now where the central ray of the camera hits the screen.
    • Image is now pitched down.
    • Fill projection. Make longitudes straight.
    • Latitudes are circles.
    • Do not try to line up outer circle with screen — just cover the screen using 4-point warp.
  • Now figure the angles
    • Find out which pitch the main view has
      
      • ZERO (0,0,0) is still the sphere center.
    • Figure start angle
      • There are 10 latitude lines on our test image, numbered (0,) 10, 20, .. 90 (, 100), like percentages.
      • Figure which would be the equator of a globe (you might even think of some extra line somewhere between).
      • The number E gives a ratio:
        
      • For example: Equator (biggest circle) is the middle of line 70 and 80. This makes E=75%, thus
        
      • Use this angle in “fisheye to spherical dome”-conversion.
    • Figure view poses
      • Eye is always 0,0,0.
      • View poses are basically the same as with a  standard camera position, but pitched.
      • Create “main view”, which is pitched (rotation around x) by 30°, -y is up, that makes roll (rotation around z) 180°.
      • Do auto pose.
      • Use “main view” as relative view (SPCalibrator Version 4.3).
      • Make them nice. They should be the same as the ones used in VRSG before. Remember: screen, projector position, and “forward” have not changed!