From the user's point of view parametrics means the control (manipulation) of
geometry by manipulation of suitable parameters, i.e. values, which influence
the geometry in any way. This may be, for example, the value of dimensions or
co-ordinates.
SISCAD-P is conceived as a relational system. Thus, the possibility to
parametrically modify the geometry is an integral part of the core system and
not an additional module. Due to the relational data structure all necessary
information is saved within the internal CAD model.
The parametric concept bases on 3 columns:
Constructional relations are relations between geometrical objects that
describe the way how one or more objects have been created and which other
objects or parameters have been involved in this construction.
These relations between the objects automatically occur during the construction
process and may be saved by the system. Any later manipulation will be
considerably influenced due to these relations.
Constraints determine certain positional and dimensional constraints of an
object. Possible constraints can be fundamental geometrical properties, as for
example, parallelism of two lines or more complex properties, as for
example the determination of the position of a point on the center of a
line.
In general, the objects concerned are by far not as restricted when using
constraints for any later manipulation as by saving constructional relations.
The constraint parallelism of two lines , for example only determines that
these lines are parallel and remain so even after a manipulation. The position
of the lines to each other or the length of them, however, is not determined;
thus it is free.
Variables, functions and formulae form the 3rd column of the parametrics
concept of SISCAD-P.
Variables are wildcards for any parameter and can be called
with their variable name. When using a variable for the construction of an
object the current content of the variable is inserted.
To determine parameters you may not only use simple variables, but also
functions and complex arithmetic expressions
(formulae) can be entered.
Each of these 3 columns is suited for a particular range of applications.
You may decide for each case, which method is the most sensible one for your
individual application.
The following sections describe these methods. The meaning of
parametric dimensions is particularly emphasized.