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Add Rho control to elliptical blends (#3640)
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NickB  
#1 Posted : Friday, February 18, 2011 4:10:57 PM(UTC)
NickB

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I find that I use the 2D conics a lot, and really appreciate the control that they provide of Rho, particularly with the 4 point conic tool.

Is there any way that you could add Rho control to the solid elliptical blend tool so that users can get more control over parameters.

At the moment because this feature does not exist. The work around is to create a 2D conic with the Rho that I want, then close the profile into a form that can be extruded, extrude - which usually requires creating a series of rails that have been derived from the sections I want to blend, and boolean the resulting solid into place. This is doable for corner blends, but really hard for an edge blend where you are experimenting to find something that looks good, as it means trimming a section of the model out so that the blend will fit in. Now try doing this over a complex surface that is not flat. Adding a blend can take hours to get right instead of seconds.
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Nick R  
#2 Posted : Saturday, February 19, 2011 6:00:20 AM(UTC)
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I agree with Nick. This would be a really useful feature. I have used this method to create this type of blend, It is something demanded from one of my clients as they will not accept the look of constant radius blends and this can be really difficult to do for all but simple shapes. If you to make changes then it is so slow.
Maybe an acceptable alternative would something like the Elliptical Blend with three components to the blend 1. a lead in radius 2. the main radius 3. a lead out radius (which would probably be the same as 1.).
This feature is the one outstanding that I would love to see included in Shark. Bug fixes are fine but most of them can be worked around now. This feature would really be moving Shark along and could say be a differentiator to Viacad.

Nick Robinson
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blowlamp  
#3 Posted : Saturday, February 19, 2011 6:26:45 AM(UTC)
blowlamp

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Could someone post a picture (or file) of this, as I'm finding it hard to visualize how it can work and retain tangency of the blended faces?

Martin.
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NickB  
#4 Posted : Saturday, February 19, 2011 6:55:25 PM(UTC)
NickB

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Martin,
Short answer to your question about maintaining tangency and being able to change Rho on an elliptical blend:

The software should take care of tangency for you in the same way as it currently does with elliptical and radial blends.

Screencast shows how to go about doing that with a simple blend between two cylinders.

http://screencast.com/t/yECBCklw8a
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blowlamp  
#5 Posted : Sunday, February 20, 2011 5:43:46 AM(UTC)
blowlamp

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NickB.
Thanks for taking the time to make the video and for explaining it so well. I can see what you're after now.

From your video, my understanding is that as long as the Control Point of the Conic curve is located at the intersection/edge, then the Shoulder Point can be positioned within an Rho setting of (about) 0.5 and 1.0 and the resulting blend will be at a tangent to the affected faces.

So having had a play with it myself, I agree this feature would add a very nice subtlety to the already powerful Blend tool to our CAD program.


Nick R.

Quote:-

"...and could say be a differentiator to Viacad"

Sorry I've got to disagree with you on this point, as I've 'only' got ViaCAD Pro :D :(


Martin.
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Tim Olson  
#6 Posted : Tuesday, February 22, 2011 11:34:38 AM(UTC)
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Hi Nick

I looked around in the ACIS docs but have yet to find an interface into blending that would support a rho. It's all based on radius. And there is not really a way to add a new blend cross section with the api that I've found.

Conic curves are great. The first CAD system I did for Lockheed relied heavily on conics as typically most of your airplane is built from conic sections. I think the only outer contour surfaces on the F-16 not based on conics (polyconic surfaces) were the wing surfaces. Conics dominate military aircraft design for similar reasons you mention. You can change the rho value without changing the tangency at the ends. For area ruling, where you need to change the cross sectional area to minimize wave drag, rho value editing rocks. Our AeroPack addon for Darcorp supports polyconic surfaces, but they are limited to surface geometry typically found in aircraft.

http://www.darcorp.com/Software/AeroPack/




Tim
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NickB  
#7 Posted : Tuesday, February 22, 2011 12:03:38 PM(UTC)
NickB

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Tim,
The Ployconic Surfaces and Space Splines from the AeroPack both look like they could be very useful for industrial designers who are looking to create smooth connected surfaces.

Are the Polyconic Surfaces from the AeroPack just surfaces, or can they also generate solids? (I know that I can always thicken a surface into a solid, but it is nice to not have to go there.)

Is there any way that Spatial could be persuaded to add Rho control to the API so that PolyConic surfaces could be created using the editing tools rather than from from separate geometry that is then joined to the main part?

I haven't used SolidWorks for a while, but there used to be a tool that allowed you to do exactly what I want using some preferences in the blend tool, so that the extents of a blend could be extended beyond the radius of the blend. Is there anything like that in the ACIS API?
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Tim Olson  
#8 Posted : Tuesday, February 22, 2011 12:50:57 PM(UTC)
Tim Olson

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>>Are the Polyconic Surfaces from the AeroPack just surfaces,

Surfaces. If you need a solid, you can stitch them into a solid. But they would need more work to be used in consumer product design.


>>Is there any way that Spatial could be persuaded to add Rho control to the

A bit frustrating there. Since Dassault acquired Spatial, they have ignored enhancement requests for advanced surface modeling.


>> Is there anything like that in the ACIS API?
Not that I'm aware of but will look again.


Tim
Tim Olson
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NickB  
#9 Posted : Tuesday, February 22, 2011 2:43:08 PM(UTC)
NickB

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Tim,
Thanks for looking into this.

Quote:
A bit frustrating there. Since Dassault acquired Spatial, they have ignored enhancement requests for advanced surface modeling.


Sounds like Dassault are trying to push users towards their higher priced Dassault branded products if they need more advanced control over surfaces. Pity.
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Tim Olson  
#10 Posted : Tuesday, February 22, 2011 9:33:45 PM(UTC)
Tim Olson

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Yup. I suspect CGM will be more of the same.

Tim
Tim Olson
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