Any techniques to keep parametric drawing from turning inside-out?

Joe Dunfee

 I am experienced with 2D sketch constraints on multiple platforms, but have always been frustrated by BricsCAD's version on my v14.  One of the main things, is that when I think I have a fully constrained model, it sometimes turns inside out.  I realize that mathematically, the inside out version is accurate, but is certainly no how anyone really wants a parametric drawing to behave.  

I suppose, the solution has to know to prevent changing the direction of a dimension   I.e. if the 1st point is on the left, and the 2nd point is on the right, try to find a solution that keeps that orientation.  I realize if the figure is rotated, that orientation could change, but that is less likely a scenario than stretching a drawing.

For the example, I did use the stretch command to force the inversion to happen.  But, this problem often appears when I am editing dimensional constraints as well.

Can anyone suggest an approach to prevent this sort of inversion?  See the attached drawing for an illustration of the issue.

-Joe

Roy Klein Gebbinck

I don't think there is a way to stop this from happening at least not when the _STRETCH command is used.

But if the model is only changed using the dynamic dimensions, adding dimensional constraints can be effective.
In that context it can be useful to use _DCALIGNED with the Point & line or the 2Lines option. See here.

I suggest you change your 'd2' dimension to a _DCALIGNED 2Lines dimension.
And add a _DCALIGNED Point & line constraint with this formula: 'd3+d4/2-d2'.

But, in conclusion, it is my opinion that the system of 2D constraints is flawed. The fact that you and I are indeed still struggling to accomplish what on the surface appear to be pretty basic tasks points in that direction. The biggest flaw is of course that there is no way to revert to the original model and reapply dimensional constraints. Sadly BricsCAD's own 3D constraints suffer from the last problem as well.

Joe Dunfee

 Thanks for the tip.

I know from my past experience with older versions of parametric modelers, that the 2D sketch constraints have been a challenge.  Though, by several years ago, all the big players have really improved their behavior.  Bricsys is new to the game, and still has come catching up to do.

There are a few things that I would love to see implemented, and really should be easy things for Bricsys to add, perhaps just as an add-on utility.

The following should be easy to do with a selection set;

1) A command to automatically constrain endpoints on objects that already have common end points.

2) A command to automatically add vertical or horizontal constraints to lines that are already vertical or horizontal.

3) A command to automatically add concentric constraints to arcs and circles that are already concentric.

-Joe

Roy Klein Gebbinck

Of course there is an added challenge for BricsCAD. 2D constraints are part of AutoCAD. So the BricsCAD team, in their bid for compatibly, are limited when it comes to implementing new features. But AutoCAD can create more automatic constraints than BricsCAD (I don't know how reliable or useful these are). Note: I am using BricsCAD V14.

Your wish #1 has already been implemented:
Use the Autoconstrain option of the _GCCOINCIDENT command.