To define the three-dimensional space, solidThinking, just as most computer graphics applications, uses the Euclidean-Cartesian coordinate system: three perpendicular axes (X, Y, Z) intersecting at one point called origin (whose coordinates are 0, 0, 0).
In the Cartesian coordinate system, also known as XYZ coordinate system, any point in the 3D scene is identifiable by one coordinate in the X direction, one in the Y direction, and one in the Z direction.
The coordinate system adopted in solidThinking is a Z-up world: it means that, in a world representation where the X and the Y directions are on the same horizontal plane, Z represents the up direction.
The Z-up world is certainly the most used by designers and architects, while the Y-up world, another world representation where Y represents the up direction, is often preferred by animators.
The mathematical representation of space here described can be applied to either a global or a local coordinate system.
The global (also called world) coordinate system is a coordinate system that is used to locate an object in relation to a world origin. The world origin is a reference point unique for all the objects in the 3D space.
The local (also called object) coordinate system is a coordinate system that is applicable to a single object having its own center as origin.
Any object in a 3D space has both local and global coordinates.