Linear Dimensions

DRAW Reference Manual

Dimensions : Linear Dimensions

The simplest kind of Linear Dimension consists of a pair of points on a drawing, each of which relates to a point in the 3D model. From each of these Dimension Points on the drawing, a projection line is drawn in a user-definable direction; between these parallel projection lines, dimension lines are drawn. Each dimension and projection line can have text associated with it.

Such a dimension can be produced by typing the commands, starting at Layer level:


NEW LDIM	- Create new linear dimension element
FROM ID @
TO ID @
TO ID @	- Use cursor to nominate (three) items to dimension from/to

The Dimension displays. If only two elements are hit, a pair of Dimension Point elements are automatically created, with the last point becoming the current element.

In the example the Dimension Points are DPPT elements - the Dimension Point is defined by a p-point of the Design element, in this case the origin. Any p-point can be nominated as a dimension point by replacing the FROM ID @ syntax by FROM IDP @/TO IDP @. The Dimension can also be defined explicitly:


Example:
FROM /1501A TO /1501B

The other two types of Dimension Point that can be owned by an LDIM element are:

•

DPOI - allows you to dimension to/from any given 3D positions

•

DPBA - allows you to dimension to/from ‘before’ or ‘after’ a Design element (in the Dimension direction).

DPOI elements can be created by a sequence, for example:

NEW LDIM
FR POS @ TO POS @

DPBA elements can be created by a sequence, for example:

NEW LDIM
FR BEFORE ID @ TO AFTER ID @

The effect of such a command depends upon the dimension direction. Refer to Principal Attributes of Angular Dimensions for further information.

The example illustrates a linear dimension, produced by the same command but with different dimension directions.

Constructed points can also be used to create Dimension Points. Refer to Point and Line Construction for further information.

Note:

In cases where the dimension value is less than 0.01 mm, the display of all dimension point graphics is suppressed.

When dimensioning BEFORE or AFTER elements, for example, EQUI, STRU or SUBS, DRAW ignores those primitives with OBST (obstruction level) set to 0 or 1. When dimensioning BEFORE or AFTER a primitive, its OBST value is ignored.

The example illustrates the use of ‘before/after’ linear Dimensions with a single element. DOFF and OSHT are described. Refer to Principal Attributes of Linear Dimensions for further information.

Note:

Under some circumstances the length of the projection line for a DPBA can be unsatisfactory. In this case changing the value of the NPPT attribute (which supplies a reference p-point) corrects the situation.

Note:

Use of Radial Dimensions can provide a simpler method of drawing the two dimensions as illustrated on the right-hand side of the example. Refer to Radial Dimensions for further information.

Note:

Any combination of the three Dimension-creating commands is permissible.


Example:
FROM ID @ TO BEFORE ID @ FROM POS @ TO ID @ FR AFT ID @ TO POS @

Each FROM command sets the Dimension Point’s DDNM (Design Data Name) attribute to the Name of the Design element. The DDNM attribute can be reset immediately to define a new Dimension Point. If the DDNM is set to refer to an element, which is not in the Id List referenced from the current VIEW, the Dimension is still drawn.

The command:

CHECK REFS WARN

causes a warning to be output in this situation, and the command

CHECK REFS FULL

results in such Dimensions not being drawn. The default reference-checking mode (for example, no checking) is given by

CHECK REFS OFF

Reference checking is also available for Labels. Refer to Labels for further information.

It is possible to draw a Dimension that contains Dimension Points that are incompletely defined (for example, a DPPT with an unset/illegal DDNM). The Dimension is now treated as only containing the significant Dimension Points for both drawing the Dimension and for commands which rely on the drawn dimension (for example, PLCL @ (refer to Principal Attributes of Linear Dimensions for further information) and DTOF @ (refer to Detail Attributes of Linear Dimensions for further information)).