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# Combination Editing (OBJECT EDIT)

Before being able to enter the OBJECT EDIT state (i.e. edit non-terminal), it is necessary to pass through two intermediate states in which the full path of an object to be edited is specified, and the location of one arc along that path is designated for editing. It is possible to create a transformation matrix to be applied above the root of the tree, affecting everything in the path, or to apply the matrix between any pair of nodes. For example, if the full path /car/chassis/door is specified, the matrix could be applied above the node ``car'', between ``car/chassis'', or between ``chassis/door''.

The transformation matrix to be applied at the designated location can be created by the concatenation of operations, each specified through several types of user direction. Trees can be rotated around the center of the viewing cube; this rotation can be specified in degrees via keyboard command, or can be controlled by the rotation of a set of control dials or motions on a three-axis joystick. Translation of trees can be specified in terms of a precise new location via keyboard command, or by adjusting a set of control dials. Tree translation can also be accomplished by pointing and clicking with the mouse or tablet. Uniform and single-axis (affine) scaling of a tree can be controlled by a numeric scale factor via keyboard command, or by way of repeated analog scaling by pointing and clicking with the mouse or tablet. Before we discuss the editing features of MGED, we will discuss how one selects objects for editing.