Hi All

Can any tell me why the option Show points (Show pts) stops to funktion after
an Boolean operation ?

Where do all the points go ;-)

- Frank

Hi Will,

> I know you've frozen development now but some kind of option to set the
> display resolution

This is actually currently available under Options / View / Meshing parameters. You can adjust the angle there, putting it down to an angle of 5 actually will solve this particular example. However, I don't really recommend doing that for normal operation because it will cause rather excessively dense meshes for many other objects, which will tend to bog things down on more complex models.

Right now the display meshing is driven totally off of angular measurements, and that doesn't work very well for stuff that's a bit larger on the screen but only has very shallowly curved stuff. To fix this really means making the display mesher look at more than just the angle, like possibly the distance gap between the mesh and the surface. But the big advantage to only angular measurements is that they are scale independent, that is they don't work differently on a large sized object versus a small sized object, they purely work off of the curvature of the surface. Distance measurements tend to have issues from differences in the overall scale of objects.

This is a very sensitive area for performance, it would be easy for me to make things denser to make this look smooth, but the trick is not to make everything too dense by default and bog other things down unnecessarily.

I've collected several examples of this kind of shallow mesh problem, and at some point I'll try to fix it up, but it's not really an area where I can do a quick fix. Any changes in this area will require a lot of performance analysis to make sure that it doesn't slow things down.


> or perhaps a dynamic option that based on the number of entities (or
> perhaps screen redraw time) could up the resolution until things start to
> slow down when redrawing?

That might be possible at some point, but it's really pretty difficult to pull off well - meshing in general tends to be a pretty intensive calculation, and it can be hard to try and slip in an intensive calculation right in the middle of something like view rotation. It tends to kind of have a stuttering effect. It's kind of easier to ensure smooth view operation by just getting all the meshing out of the way at the start like it currently does.

- Michael

Hi Frank, MoI won't let you turn on points if you have an object made up of joined surfaces where each surface has a different control point structure. This can happen easily when surfaces are intersected such as in the boolean commands.

The points are not shown in that situation because it would be too easy to drag the points for one surface and cause a gap to happen along what should be a shared edge, that would tend to put a hole inside what should be a solid skin.

You can view the points by using Edit / Separate to break your joined object into just individual separate surfaces. You can always show points for an individual surface because it does not have this "pull apart shared edge" issue.


Here are some pictures that I hope will help explain it.

Here is a plane and a cylinder that I have booleaned together:



Here are the control points for the cylinder:



Note how there are no control points along the intersection edge with the plane - that edge is what is called a "trim curve", it is a curve that has been calculated that exists on the surface, but is not directly connected to the control point structure of the surface. So you can't modify the surface by pulling on the trim curve itself, the trim curve has its own control points that are separate from the surface's control points.

Here are the points for the plane, just 4 points at the corners:



So you can see here that the 4 points for the plane do not match up in any way to the control points for the cylinder. Here is what happens now if I grab one of the points of the plane and drag it, it opens up a gap:



This is kind of a fundamental thing for how NURBS modeling works, it has to do with the creation of those "Trim curves" that live on a surface but are separate from the surface's control points.

Once you have things set up connected by trim curves, you can't easily modify things by moving surface control points and still have the connections between the trim curves stay intact.

So the whole trim curve system does not lend itself to point squishing, however it is also the key thing that makes boolean operations work well with NURBS models (as opposed to polygon models), since as you do multiple boolean operations the surfaces themselves don't change, just new trim curves are calculated. With a polygon modeler, each boolean operation actually dices the polygon surfaces themselves up into a whole lot of small pieces.

Hope this helps explain it some!

- Michael

Thanks for the explanations, Michael - yes, I had went into the option and bumped it down to 5 but I agree, that's probably not the best solution even though granted, I don't normally have heavy models in MOI.

I will say though that spacestation of mines did start to slow down the view a bit with all the fillets I had added...


I just wish I had known that what I was seeing wasn't what I was going to get at export time - there were several objects I rebuilt because they didn't follow the curves after the extrusions...

-Will

Thank you very much Michael for the fine example.

:-) Frank