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ammobake

Question about ruled surfaces

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ammobake
Posted (edited)

This is related to a project I've been working on in another thread but figured it deserved its own thread since it's a different question.

I've been using AutoCAD 2019 for this.

 

My question is how to get AutoCAD to correctly draw the ruled surfaces at locations with sharp angles (or is this possible?).

AutoCAD always seems to make the ruled surface cut across at sharp angles.  For example..

 

3764433_meshedges.thumb.jpg.b0d89f0ea7e14216a6671737e8528ac5.jpg

 

At topright is a 3D Loft with the desired result.  At lower left is a ruled surface with this weird angle on the end - both using the same blue polyline which represents one of the aircraft cross sections.

I've experimented with using higher SURFTAB counts but the same curve remains.  It's apparent loft doesn't always have this same issue.

 

The angle is the result of surface smoothing.  So, basically, it draws a straight line across those 2 edges.

 

For values SURFTAB1 and SURFTAB2 I've been using 60 and just using smooth later on for appearance.

I've experimented using higher tabulation counts but they don't appear to affect this curve.

 

Perhaps the algorithm used to create ruled surfaces has some kind of set value that cuts across when 2 edges reach a specific distance apart?

 

The only solution I can think of is manually manipulating the mesh grips to stretch this thing out.  I could also delete all these meshes and use lofts but don't want to waste the work lol.

 

-ChriS

Edited by ammobake

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lrm

If you look up the documentation on rulesurf you will see that it states:

 

The ruled mesh is constructed as a 2 by N polygon mesh. RULESURF places half the mesh vertices at equal intervals along one defining curve, and the other half at equal intervals along the other curve. The number of intervals is specified by the SURFTAB1 system variable. It is the same for each curve; therefore, the distance between the vertices along the two curves differs if the curves are of different lengths.

 

Note the "equal intervals". If you want the ruled surface to use the vertices then explode the polyline or use loft.

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ammobake

Thanks! I was able to explode and join the corresponding segments together.  I just drew ruled surfaces between each segment.  I then used merge (union) command to join them and convert the whole thing to a smooth 3d solid.  The loft command usually gets the preferred result but in this case it didn't, for whatever reason.

 

-ChriS

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