Datasheet

ORDINATE
Ordinate dimensions are used to set dimensions as coordinates in the X and Y axes. Ordi-
nate dimensioning is used most often in mechanical drawing, but it’s increasingly being
used in architectural and other fields as well. When I draw a structure that I’ll be building
myself, I always dimension it with ordinate dimensions rather than with continuous
dimensions, which is the traditional method. That way, I can hook a tape to one end of a
sole or top plate and mark all locations of openings from a fixed point.
Although there’s a DIMORD command, the quickest way to place ordinate dimensions
is with QDIM. Select the points you wish to dimension, and then select a new datumPoint
for 0,0. Now you can choose the Ordinate option, select your objects, and place all ordi-
nate dimensions with one pick. If you have objects with different base points, use the
datumPoint option again.
If you don’t use QDIM, you must first establish a new base point by setting a UCS with
its origin at the 0,0 location on the part you’re dimensioning. Use the UCS command,
select the Origin option, and then select the 0,0 point on the part. If UCSICON is ON and
set to ORigin, the icon representing the UCS moves to the new origin point. AutoCAD
automatically places the correct distance in the X or Y direction, depending on which
direction you move from the dimension origin point you pick.
These dimension values are associated with defpoints, not the objects themselves, if
DIMASSOC is 1 or 2. This association is maintained for the UCS that was current when
the dimension was placed. Stretching the defpoints of the dimensions results in the values
being updated correctly, even if a new UCS has been set since the dimension was created.
Dimension Variables
AutoCAD 2007 includes 79 dimension variables. The easiest way to change them is using
the Dimension Style Manager dialog box. You don’t have to know all of them, but there
are two you should understand.
DIMASSOC
This variable was added to AutoCAD 2002 to control associative dimensions. It replaces
DIMASO, but not completely, because earlier drawings can be opened in current releases.
When an earlier drawing is opened, the setting for DIMASO is used to determine the
value of DIMASSOC.
To facilitate the use of ordinate dimensions, you can place points using the POINT command
at every location you wish to use as an origin. Using either the FILTER or QSELECT command,
you can now select only points. Doing so prevents you from inadvertently selecting too
many objects.
feature review (all releases) ■ 31
09939c01.qxd 12/5/06 3:59 PM Page 31