Up: SISCAD-P Parametrics Previous: Formulae

# Parametric Dimensioning

Conventional types of dimensioning (e.g. reference dimensioning in SISCAD-P) are associative, i.e. after the geometry has been modified the dimension values automatically adapt.
Parametric dimensioning delivers the associativity in the opposite direction.
Definition:

> A parametric measure is a measure which can only be changed by modification of its dimension value. If this is the case, the dimensioned objects automatically adapt. Other manipulations, as for example moving or rotating do not effect the dimension value as well as the geometry.

This type of dimensioning is the prerequisite for a parametric system.
Working with Parametric Measures
To be able to create parametric measures, 2 requirements have to be met:

- activated parametrics
  The parametrics is activated after having loaded a parametric construction or after having entered the command

  > MODIFY PART PARM OP=<id>;PRC=1

  to explicitly activate the parametrics.
  Note: When parametrics are activated, the symbol auto constraint mode is displayed in the main menu (not only after starting SISCAD-P).

- yellow dimension
  The measure displayed under the symbol info parametric has to be shown as possible parametric measure, i.e. in yellow. To change the color for the dimension, you have to click the corresponding symbol in this menu.

Default is that a reference dimensioning is created, i.e. parametrics is inactive and the measure is green.
The syntactic rules for the creation of parametric measures resp. reference measures are the same, but not all available types of dimensioning are possible for parametric dimensions.
For easier differentiation parametric measures are displayed in yellow and reference measures in green. They are also assigned to different layers.

To parametrically dimension geometrical objects, they must not be exactly determined, i.e. the should have some degrees of freedom left. If they are exactly determined, SISCAD-P does not create a parametric measure, because it would not be possible anymore to react to a modification of the nominal size.
Example (parametrically dimensioned lines): 2 finite lines (g1 and g2) with a common starting point are constructed right-angledly. Parametric constraints or constructional relations are not saved.
Now you can create a parametric angular measure between these two lines. The corresponding command reads

> CREATE ANGULARDIM BTWL REFL1=<id>;REFL2=<id>;PDL=<pos>!

Figure 6: Right-angled lines with parametric angular measure

The color of the measure is yellow to see that this is a parametric measure.
Because of the modification of the nominal size to 45 (for this purpose you have to enter the command: MODIFY NOMINALSIZE OP=<id>;VALUE=45! ) the lines adapt so that the desired value is reached.

Figure 7: The lines after the modification of the nominal size

But: If, before the creation of the angular measure the constraint PERPENDICULAR has been saved for the two lines (REMEMBER PERPENDICULAR), the attempt to create a parametric angular measure causes the following prompt (or a similar one) to appear:

> "The geometry would be in an inconsistent or overdetermined condition after this action. The geometry or dimensioning that is the reason for this will be displayed."

The command is not executed. Actually there would not be an inconsistent condition after having entered the angular measure, but the system recognizes that it cannot react to a modification of the nominal size.

Up: SISCAD-P Parametrics Previous: Formulae