All,

I'm working on a model of a BQM-34A Firebee, an aerial target drone for the Military.

Here is what the real thing looks like.




I'm having some difficulty when trying to combine 3 shapes that make up the engine intake.

Here is a snapshot in MOI of the intake.



Now, when I Trim away the unwanted curves and Join it altogether, I end up with corner points, mainly at the Arcs.


Here it is before I Join the sections.


And here it is after Joining. This looks odd in and of itself, because of the point spacing on the circle.
This didn't happen originally. It showed up as I was preparing my question. I'm not sure of what is going on here either, anyway.


And finally here are the strange corners that I wind up with.


I'm using the Jun-27-2014 beta build.

How can I create this without corner points?
Is there a better way?

Thanks in advance for any help.


Scott

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Hi Scott, the "real" control points for an exact circle actually look like what you see there on the top with the segmented pieces. As you see they're not very squishable because of those corner points between arc pieces.

When you turn on control points for a circle, MoI actually shows you control points of an automatically rebuilt version since it assumes that you want to squish around some of those points and that you want a squishy result.

That kind of alternate "squishy" points method will only happen if a whole curve is an exact circle, arc, or ellipse, not when only one segment of it is. That's why you get the different look after the join.

Probably the easiest way to get a squishy result without corner points is to use the Rebuild command on it, see here for some info:
http://moi3d.com/2.0/docs/moi_command_reference10.htm#rebuild

The Rebuild command will reconstruct a curve by sampling points along it and building a new curve going through those points. Part of what it does is if you have smoothly meeting segments (different segments will always meet at a type of point that will make a sharp corner if you disturb it, they're basically different curve pieces glued together at their endpoints only) it will take those segments and build just one single smooth segment out of them.

Since you want squishable pieces it also may not be bad to run Rebuild on your circle before you join it in, that will convert it from one of the "exact but segmented" circle type splines to a general spline that does not have any internal segmentation in it.

Let me know if any of this does not make sense. Basically often times for precise conic section curves (exact arcs, circles, ellipses, etc...) they are often made up of internal sub segments which then do not deform very well.

- Michael

Hi Scott, I've attached an example here - I used Rebuild with a tolerance of 0.02 units (so it means this curve is up to 0.02 units away from its previous shape), which has removed all the internal corner points so it will squish around better now.

- Michael

Thanks for your response bemfarmer.

Thanks for the clarification Michael.
So, is it always a good idea to run "Rebuild" on blended and joined segmented curves, arcs and the like?
Provided you don't want any corner points that is.

scott

Hi Scott,

> So, is it always a good idea to run "Rebuild" on blended and joined segmented curves, arcs and the like?
> Provided you don't want any corner points that is.

Yeah usually it is a good idea to use it if you want the segmented joined curve to behave as one single smooth piece after you move some of its control points around in the juncture areas.

In the future I think I'm probably going to try and incorporate some kind of "rebuild and merge segments" type of mechanism directly inside the join command itself.

- Michael

Hi Michael,

Yeah, incorporating that into the Join command, would be convenient.
Really enjoying the V3 beta.
I'll definitely upgrade once it's finalized.

Keep up the hard work and thanks again for the clear explanation.

Scott