VARKON Version 1.15 1997-10-16
A group is a non geometric entity with a name and a list of members.
In its simplest form a group can be used to associate a text with
a single entity.....
arc_1pos(#1,vec(0,0),10);
group(#2,"screwhole",#1);
In this example a group is created with name = screwhole and the
arc #1 is its only member. The significance of this would be that the arc
represents a screw hole, information that could be used for example by
another application during process planning or cost estimation. The group
entity is implemented using two way pointers between the group and
its members. The arc entity knows which group it belongs to and
the group entity knows where its members are.
A group can also be used to combine several entities into a common
structure...
poi_free(#1,vec(0,0));
poi_free(#2,vec(100,0));
poi_free(#3,vec(50,50));
group(#4,"triangle",#1,#2,#3);
In this case a group #4 is created with three points as members
and name = triangle. Each point holds information that it belongs to group
#4 and the group itself holds its name and the identity of its three
members. Any entity including group itself can belong to a maximum
of 3 different groups at the same time.
The group entity is a way to create a structural relationship or
context in much the same way as the part. A part is more
powerful but also more complex to use. A part needs a defining MODULE,
uses parameters and holds any number of entities while a group only
has a name and can only hold a maximum of 100 members.
In many cases it turns out best to use the part to describe different
objects and the group to describe smaller structures within the
object. A group can also be used to express a relation between two
different parts.
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