2011

underconstrained geometry Objects with unsolved degrees of freedom are underconstrained.
underground The XY plane of the user coordinate system when perspective projection is
turned on and when viewed from below ground. The underground plane displays with a
color gradient between the earth horizon (nearest to the horizon) and the earth azimuth
(opposite the horizon). See also ground plane and sky.
underlay A DWF, or DGN file used to provide visual context in a drawing file. Underlays
cannot be edited, and do not provide the full range of notification. Underlays cannot be
bound to a drawing. See also external reference (xref).
up direction A vector defining what direction is Up. By default this is the positive Z – axis
(0,0,+1).
The up direction and the north direction are always constrained such that they are
perpendicular to each other.
user coordinate system (UCS) A user-defined coordinate system that defines the orientation
of the X, Y, and Z axes in 3D space. The UCS determines the default placement of geometry
in a drawing. See also world coordinate system (WCS).
user parameter Named user-defined variable (real number or an expression) that can be
used in expressions for dimensional constraints or other user parameters.
UVW The material’s coordinate space. Used instead of XYZ because that is usually reserved
for the world coordinate system (WCS). Most material maps are a 2D plane assigned to a
3D surface. The U, V, and W coordinates parallel the relative directions of X, Y, and Z
coordinates. If you look at a 2D map image, U is the equivalent of X, and represents the
horizontal direction of the map. V is the equivalent of Y, and represents the vertical direction
of the map. W is the equivalent of Z and represents a direction perpendicular to the UV
plane of the map.
value node A specific type of action node that is used to handle requests for user input and
hold the recorded value that was captured during the recording of an action macro.
value set In a dynamic block definition, a range or list of values specified for a linear, polar,
XY, or rotation parameter.
vector A mathematical object with precise direction and length but without specific location.
vertex A location where edges or polyline segments meet.
2676 | Chapter 52 Glossary