E-space, Base, Axis and Extents

Entity Space (E-space)

The E-space is a private coordinate space for an entity, and is described by three fields within the entity structure: local_base , local_horz and local_vert. The local_base is the origin of the E-space, in world space coordinates. local_horz defines the direction of the positive x-axis of the space. local_vert defines the direction of positive y-axis of the space. The initial orientation of the E-space is dependent on the C-Space that is in effect when the entity is created.  The E-SPACE command may be used to change this orientation.

Base Point

The base point is used for commands that involve scaling, rotation and shearing.  The base point is stored in the center field of the BOS_NODE.  This field receives a value when the entity is scaled, rotated or sheared.  A value for this field may also be established manually by the FIX BASE command.  The definition BITS_CENTER is defined on bits1 and indicates whether or not the base point has been established.

Axis of Rotation

Two points which define the axis of rotation are stored in the axis_top and axis_bottom fields of the BOS_NODE.  These points are established when the entity is rotated axially.  These may also be established manually by the FIX AXIS command.  BITS_AXIS, defined on bits1, indicates whether or not the axis has been established.

Extents

The extents of an entity are the maximum and minimum x, y and z world space coordinates of the entity. This data is described by the high and low fields of the BOS_NODE. The maximum is held in the high field; the minimum is held in the low field.  Entity exents may be retrieved through direct access to the BOS_NODE or through the use of the bos_extents function.