CG Coordinate Systems
Nearly all post production tools in the 3D computer graphics world are based around a 0,0,0 origin as the center of the ‘world’. The reason for this is straightforward; since a computer has a limited number of bits to represent a number, one can get into strange numerical errors when one uses very large positive or negative numbers to do all of the transformations that computer graphics requires.
Surveying Coordinate Practice
It is common practice in surveying to start off with a very large positive number, to avoid having any negative values in the survey. However, as can be guessed, this conflicts with the practice needed in computer graphics.
Previzion Surveying Practice
Since Previzion is a 3D computer graphics system, and both sends and receives 3D data from other post production computer graphics systems, its world is also based around a 0,0,0 center. The recommended practice is to specify some point relatively near the camera to be 0,0,0, and to point the +X axis away from the camera and the +Z axis to the right of the camera. This matches cleanly with the standard total station use of northing, easting, and elevation axes:
- Northing = +X
- Easting = +Z
- Elevation = +Y