1. Basic Coordinate Systems & VR
Babu 2011

2. Changing between coordinate systemsz1 y2 x1 z2
Coordinate Systems 1 x2
Coordinate Systems 2
Babu 2011

3. What information do we need?
Distance between origins: [x,y,z] and rotations of coordinate system axes of coordinate system 2 to line them up with coordinate system 1 axes
Transformation matrix between the two coordinate systems
Babu 2011

4. Coordinate Systems in VEs
Tfrom Chair’s coordinate system to Room’s coordinate system
Room
Door
Table
Chair
Vase
We usually deal with multiple coordinate systems in a virtual environment
Scene is collection of geometric objects
Geometries are usually defined relative to a local coordinate system
Coordinate System Graph is used to relate all geometries to the virtual world that we are presenting
Babu 2011

5. Where is the “eyepoint” in a HMD
Sensor x y z
Tracker gives position and orientation of Sensor’s coordinate system relative to the Source Y Z X
Your eye is not on the top of your head!
(0,0,0)
Electromagnetic Tracker Source
Babu 2011

6. Where is the “eyepoint” in a HMD
Sensor x y z
Your right eye is a fixed distance and orientation from the sensor (which you must measure based on the configuration of the HMD and sensor). Y Z X
(0,0,0)
Electromagnetic Tracker Source
Babu 2011

7. The eyepoint also has a coordinate system!
Sensor x y z Y Z X
The image source and the optics of the HMD define a “screen” that is located a fixed distance from the eye (projection plane in graphics terminology) and moves with the head.
(0,0,0)
Electromagnetic Tracker Source
Babu 2011

8. Coordinate System Graph
Each node represents a coordinate system, each edge linking the nodes represents a transformation between those coordinate systems
Babu 2011

9. Coordinate System Graph User Model
Modified when user uses joystick or other virtual method to walk or fly in the world
World
Constant orientation and translation
Workspace
Tracker Source
Measured by Tracker
Constant orientation and translation
Head (Sensor)
Right Eye
Left eye
Projection Plane
Projection Plane
Babu 2011

10. Coordinate System Graph User Model
Modified when user uses joystick or other virtual method to walk or fly in the world
World
Constant orientation and translation
Workspace
Tracker Source
Measured by Tracker
Constant orientation and translation
Head (Sensor)
Right Eye
Left eye
Projection Plane
Projection Plane
Babu 2011

11. Tracker allows the user to move through a small subset of the world
Babu 2011

12. Coordinate System Graph User Model
Modified when user uses joystick or other virtual method to walk or fly in the world
World
Constant orientation and translation
Workspace
Tracker Source
Measured by Tracker
Constant orientation and translation
Head (Sensor)
Right Eye
Left eye
Projection Plane
Projection Plane
Babu 2011

13. Virtual walking changes relative position of user and tracker to the world.
Babu 2011