Revolved polyline with incorrect wireframe when using different axis

[soupisgoodfood]

Why does WCS change the way solids are created when revolving a polyline?

I’ve been working on some polylines that I want to revolve. Even though it is really a side elevation drawing, I started drawing on the top plane. I did test revolves and they worked fine.

Then I decided to rotate the polylines so they appeared as the right side in the WCS (90 on the X axis, then 90 on the Z axis). But after doing this, whenever I revolve the polyline, the ring shape it forms is correct, but the wireframe doesn't look right, as it has two poles where lines meet to a point, like the top and bottom of a sphere.

I thought it was because I had been changing the UCS. That doesn’t seem to be the case, as if I reset the to the WCS it still has the same problem.

So, I’m not sure what I’m doing wrong, as I thought that it shouldn't matter what axis I revolve around (going from using the X to the Y axis) as long as it’s the correct axis relative to the plane of the polyline. I guess not. Or is it something else?

I’ve watched a few of the video tutorials on Lynda.com again to try and find where I’m going wrong, but didn’t find anything.

[soupisgoodfood]

Here's a screenshot of what I'm talkng about.

[soupisgoodfood]

No replies because this is an obvious/silly question, or because no-one can figure out why it's doing this?

[hgasty1001]

Hi,

Try posting a dwg, so someone can test it.

Gaston Nunez

[soupisgoodfood]

The yellow layer called "base profle" is one of polylines I'm trying to revolve.

The first file is after I rotated the drawing.

The second file is after doing the revolve.

[hgasty1001]

i,

I can't reproduce the problem, I've just created a revolve solid, and the mesh looks right to me, this was my procedure:

1.-Rotate (command rotate) the polyline profile 90°

2.-Revolve (command revolve) the profile arround X axis 360°

Gaston Nunez

[dbroad]

I just used revolve on the yellow profile about the y axis and it worked fine.  If the rotation is off you can rotate whatever either before or after the revolve.  My solid seems to have a sparser mesh.  

[soupisgoodfood]

Thanks. It's working now. At first, I rotated it back 90 on the Z axis so I could revolve it around the X axis, like yours, and it worked. Then I tried it again the way I had it, and it worked. I thought maybe I selected multiple items the first time and that might have been the problem, but I tried that and it's also fine. So not sure how I ended up with the odd geomerty.

[SEANT61]

That’s an interesting distinction.  The Y axis of revolution produces a solid based on a trimmed Sphere.  Realigning for an X axis of revolution bases the solid on a non-trimmed surface. 

Those pole lines shown in the image are just that. They appear when the ISOLINES system variable was set at 256, and AutoCAD uses a trimmed sphere as the geometric representation.  (They also show in dbroad’s file with a similar system variable, setting).  Due to the dissimilar geometric base, they do not appear in gasty1001’s file. 

[soupisgoodfood]

Yeah, I was wondering if that "contour lines per surface" setting had anything thing to do with it. I didn't think it would because it's under the 3D display settings, so I assumed it wouldn't affect the way the solid was formed, only how it appeared in the viewport. I can't remember if I changed that setting before or after using the revolve command as I probably played with the revolve command a couple of times before settling on the result and may have changed the contour lines in-between.

Do you think this is intentional, or just a quirk of how AutoCAD calculates geometry?

[SEANT61]

It may just be an order of operation quirk. 

Conceivably, the modeler is set to use a sphere if center of revolution intersects with center of arc.  The modeler algorithms may also have a Pole/AxOfRev Orientation format that allows the poles to remain after trim in some orientations and not others. 

The poles may have been trimmed away in gasty1001’s file. 

Possibly, some subsequent optimization procedure simplifies the surface if possible.  With the geometry where the poles remain, simplification is not possible.

In the image below, I exploded the solid, converted the surface to Nurbs, then set the CV points to visible.   Notice the underlying geometry is different depending on orientation.

[soupisgoodfood]

I'm encountering the same problem. Except this time I can't get it to work no matter what axis I revolve on or how I rotate the polyline to start with. Some of the polylines revolve fine, even though they have the same radius (and therefore could also be formed from a clipped sphere), but one is being stubborn.

Is there way to force AutoCAD to generate the geometry the way I want it to?

[SEANT61]

I don’t know of any variable that will force a particular behavior. I gave a modified LOFTPARAM variable a try but that did not change the result.

I agree that the revolve style of surface would probably be more efficient from a binary storage standpoint, and may even look cleaner – especially with an elevate ISOLINE setting, but is there any other reason you want to avoid the visible poles?