Coordinate Systems
Use
In 3D graphics, a coordinate system is a method by which points are represented in space. As their origins are in different places and their axes are aligned differently, each system has its own uses.
The 3D Editor movement, rotation, and scaling tools are based on the system selected in the 3D Editor toolbar . The camera movement is based on the system selected in the right-click scene menu.
Features
Local Coordinate System
This system relates specifically to the selected object. Each object has its own local center and coordinate system as defined by the location and orientation of the object’s pivot point. The local center and coordinate system of an object combine to define its object space.
The direction of the object’s X, Y, and Z axes depend on the current transforms of the object, in contrast with the world coordinate system. The position of the object is actually the position of the local origin.
You can see the difference between the two coordinate systems when you unintentionally rotate an object, such as the wheel on a car, around the world axis instead of the object’s local axis. The wheel immediately flies off in a large arc because the center of the rotation is at the origin of the world coordinates. To rotate the wheel correctly, the local coordinate system should be used. The wheel then rotates around its own hub, which is the origin of its local coordinates.
Parent Coordinate System
This system is based on hierarchical relationships; child objects using the parent coordinate system are actually using the parent’s local coordinate system.
Objects at the top level of the hierarchy are considered to be children of the scene itself, so in this case the parent coordinates equal the world coordinates.
This system is mostly relevant when using the rotation tool.
World Coordinate System
This system forms the “base” on which you can think of all other coordinates being defined. Usually, its origin is at the center of the scene, and its axes might be aligned with directions like north/south, east/west, and up/down. For example, it is very common for the X axis to be east, the Y axis to be north, and the Z axis to be up. This is the coordinate system in which most of the level geometry is defined.
World space is the universal coordinate system that the software uses to track objects in the scene. World space is constant and immovable. In the world coordinate system seen from the front, the X axis runs in a positive direction to the right, the Z axis runs in a positive direction upward, and the Y axis runs in a positive direction away from you.
Note that selecting the world system in the 3D Editor toolbar affects the 3D Editor tools; selecting the world system in the right-click scene menu controls the camera movement.
Screen Coordinate System
The screen coordinate system is aligned to the viewport and is the system upon which the near and far clipping planes are based. This command controls the camera movement along the axes when aligned with the viewport.