World Coordinate System

In a Photo4D project, users should usually choose a world coordinate system to digitize an object. This coordinate system must be a right-hand system. In addition, take the following into account when choosing the system:

• If the system is chosen so that the camera location is on or close to its x-z plane, then only Ry, Tx, Tz need to be initialized and/or recorded, and Ty and Ry can be initialized to 0.0. For example, if the object is a house or building, and most images were taken from ground, choose the ground as the x-z plane of the system.
• If two reference points are on one axis of the system, then only their coordinates on this axis need to be recorded. In addition, if one of them is set to the center of the system, then their distance is the coordinate of the other point on this axis.
• The system should be chosen so that as many points as possible have the same x, y, or z coordinates. Thus coordinates measured for one reference point can be used for more than one reference points, and the Same Coordinate(s) geometric constraints (Same X, Same Y, etc.) can increase the computation speed and accuracy. See Tips for Setting Geometric Constraint for more information.

The exact unit for the world coordinate system is not important. Photo4D computes the coordinates relative to this coordinate system. However, the coordinates of reference points and camera locations must be set consistently in the unit of this coordinate system. See Set reference points and Set Initial Camera Parameter for more information.