[cad-linux] Re: the parametric project

> P2 relates to P1, if P1 moves so does P2. Very simple but works. The
> code for this is in the latest upload on kosmos.sf.net.=20

One thing that I've seen that might help you in your thinking is
that the systems I've seen that are the most successful at parametric
all have two major 'elements' or 'themes':


1. The associations are bi-directional, and real-time.

This mean that when I change something, like move a wall, the parametric
instantly 'kick-in' and that wall will not only move elements that are
located within it (like the commonly discussed door example) but also
update all the views of said objects. This makes it possible for the
user to understand the relationships between the objects, and to see
changes instantly. Other parametric systems that I've seen that lack
this functionality, and require a manual 'update' or 'regen' run to see
changes, are much harder to deal with and waste time. For example, if
I make a change to something in Revit, Revit updates that change
everywhere that moment (which sometimes can take a while if the change
is complex). In ArchiCAD, if I make a change, I then have to go to the
views that would 'see' that change (like a section) and tell it to
update that view; this adds work, and when things don't resolve it
becomes a mess as to what's not working if you changed more than one
thing. In Revit, if the change is somehow 'illegal' (like moving a door
outside of a wall) it tells you that moment, allowing you to fix it.
That real-time feedback is important. Also, the bi-directional, is part
of this; some parametric systems I've seen wouldn't let you make
changes in any view. For example, in ADT, I don't believe you can make
changes anywhere in the project; you can only change things in certain
views. So you can't change a door on the door schedule and have that
door re-draw itself automatically, maintaining any relationships you
might have constrained it to; you have to go to the plan and change it
there. In Revit, you can change anything, anywhere, and any time, and
that makes it so much more efficient and accessible of a system.


2. Make the constraint metaphors consistent with the discipline of work.

To make a simple constrain to something in Revit, you simply draw a
dimension string between two items, and then 'lock' the string.
Now those two items will hold that relationship, the distance between
them, until you 'unlock' it. There are more complex constraints that
you can do, but, metaphorically, they work the way an Architect would
think about things. As an Architect, I'm gonna think "I want this
Desk held off of the face of that Wall there 3 feet" not "I need
this handle to reference that wall-sub-object at a blah blah blah".
Inventor, another parametric system, also deal with constraints
by common Mechanical methods and thinking; so that it's very easy
from a user to understand how to set up parametric relationships
between objects. If you system you are planning can be coded in such
a way that the various disciplines have the ability to use the metaphors
that they are familiar with to set up relationships between object than
your system will be far more accessible to lay people and will get a lot
more people using it.

Jeffrey

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