Hi Michael

I'm only posting this because I know you are a very patient man:)

I'm trying to get my head around the mesh angle. I've read all your explanations on the forum and I think I get it now. Just to be sure' can i subject you to a simple questionaire. Answer true or false:

When I reduce the mesh angle, it only affects the display mesh and does not add zillions of extra actual data points to the model.

In other words, if I export as .stp or .igs, it makes no difference what my mesh angle setting is or has been during the construcion of the model.

If I export polygon data, I can control the level of meshing quite finely with the export mesh dialog.

Thank you for participating in our survey.

BTW I love the way you have set up the meshing options for polygon export, it really works well.

Hi Steve,

> I'm trying to get my head around the mesh angle.

You're talking about the Mesh angle parameter on the Options dialog under the View section, right?


> When I reduce the mesh angle, it only affects the display
> mesh and does not add zillions of extra actual data points
> to the model.

Yes, that's correct - it only controls the display mesh used at run-time and does not insert any additional points into the original surface or solid data, and does not do anything to data that is written to any file.

However, it is not very good to set this to be too small of an angle because that can start to consume quite a lot of memory for the display mesh (and also take longer to calculate), I would recommend not going any smaller than the default 10 degrees which is already quite a bit on the dense side to make a nice looking display. If you have a complex model bumping this up to 20 or 25 degrees can help to speed up the display if it is bogging down.


> In other words, if I export as .stp or .igs, it makes no
> difference what my mesh angle setting is or has been during
> the construcion of the model.

Correct. And actually the .stp or .igs export contains NURBS surface data and not mesh data, so nothing involving meshes at all really comes into play when exporting to these formats.


> If I export polygon data, I can control the level of meshing
> quite finely with the export mesh dialog.

Correct - when you export to a polygon mesh file format a completely new mesh that has nothing to do with the display mesh will be calculated.

The display mesh is actually a somewhat messy mesh, it is oriented towards calculating a result very quickly and tends to try to get a dense result as quickly as possible.

The export mesh does a lot more intensive number crunching to calculate a higher quality mesh that has stuff like more evenly spaced points in it. It is not very feasible to do this for display purposes since it takes a long time to calculate, you would have a significant pause after every operation if it tried to do this for the display mesh.


So yes, you've got everything right there, the display mesh system is a separate thing from the export mesh, and the display settings do not have any effect on saved data of any type.


> BTW I love the way you have set up the meshing options
> for polygon export, it really works well.

Thanks, I'm glad you like it!

- Michael

Thanks Michael, that's great to get that cleared up.

I guess sometimes it has to be a compromise between display speed and "prettiness" of the displayed mesh. I have a situation where one element of the model involves a long shallow arc, a bit like this discussion

http://moi3d.com/forum/index.php?webtag=MOI&msg=1308.2

So the display only looks right when the mesh angle is 2 or 3. But another part of the model needed some fine filleting work which took way too long at that mesh angle setting.

Steve

Hi Steve, yeah that kind of shallow arc situation really needs a separate mechanism to refine those.

Cranking the angle down to 2 or 3 degrees would solve that particular problem, but it will cause a really, really huge increase in density in a lot of other places.

Currently you just have to ignore that type of shallow arc poor display problem for the time being, it is just a display artifact and doesn't mean that your actual surface data is bad, and when it comes time to export the export mesher is not as sensitive to it in the same way that the display mesher is. The display mesher takes some shortcuts to speed things up, and that is one side effect from that.

It is on my todo list to fix up those shallow arc problems by using an additional "chord" measurement in addition to the angle one. That should help to get rid of that particular problem without greatly increasing the density in other places.

I haven't had a chance to get to that yet because adjustments to the display mesher have to be done pretty carefully since it affects program performance a lot. So for example I want to be careful not to slow down processing of everything in general too much, just to get that shallow arc type situation to display better. That means the tuneup has to be tested very carefully which is time consuming.

- Michael

Michael, I don't think it's really a problem, because it probably doesn't come up that often.

Steve