Extrude Along Path failure

[michaelk]

I'm hoping someone can explain what is happening.

I have an extrude along path that keeps failing, and I think I've narrowed it down to a few suspects.

It is the sort of extrude I do routinely, and have never had a problem with in the past. (vw 9 - vw 2009) Perhaps it's because of some new Parasolid engine gizmo?

I've attached a file with the path, profile and a partial extrude.

To get the partial extrude I extruded just the nose end of the profile as a polyline, then edited the EAP profile and started adding lines, one at a time, until it failed.

It turns out that I could add all the "risers" without causing a failed extrude, but I could only add lines for the first 3 "treads". Any "tread" above the 3rd caused a failure.

Any explanations / ideas?

thanks in advance

michaelk

[Pat Stanford]

Limitation in VW.

VW does not like self intersecting objects. When you do the EAP, the profile object is extruded along it's geometric center. Because of the curve in the path, the object intersects with itself.

Assuming that you actually want the "nose" of the risers to follow the path, try the following:

1. Draw a small rectangle and extrude it along the path.

2. Select the riser profile and Copy it.

3. Double click on the extrude and Edit the Profile group.

4. Delete the rectangle from the profile and paste in your riser profile. Move it so that the point you want to travel along the path is located at the 0,0 point of the window. If you don't usually have the rulers turned on, turn them on. It will help you to line things up.

5. Mirror the riser profile so it is to the right of the origin (0,0).

6. Close the polygon so the line between the bottom and top is visible.

7. Click the Exit Profile button and you will have your risers.

[michaelk]

Hi Pat

Steps 1 thru 4 are exactly what I did when experimenting. And that's how I got the extrude that I was able to get.

I use the "extrude a small profile and substitute later" trick often.

I get lost on your step five. I am able to extrude the riser profiles. It's the tread profiles that don't work.

btw, if I switch the path to a simple arc, the EAP works as expected. So I assume the problem is in the curve part of the path.

But, if that were the case, I'd expect the lower treads to fail - because they have the sharpest corners and are more likely to intersect themselves - not the higher treads.

I know, there are at least 7 other ways to do it, and I may just pick one and move on. But I'd like to understand what it is about the higher treads and the curve of this path that is causing the failure.

Once again - thanks, Pat.

michaelk

[bcd]

I may have found the problem.

The curved wings are not tangental to the center straight section. I redrew one half of it using tangent arc mode for the transition and got a result.

[michaelk]

Thanks for looking at this.

I tried using tangent arcs for the side curves on the path, but that still isn't working for me...

Any more hints on how you did it?

michaelk

[Horst M.]

Hallo Michaelk,

I just tried arround a bit, closed the Stair polygon on the back,

used the "extrude a small polygon and substitute..." trick, that

I just learned from this thread,

and there was the Tribune!

I don't know why...

May be the new parasolid Engine doesn't like open polygons ..?..

Horst M.

Edited February 7, 2010 by Horst M.

[CipesDesign]

In order for an Extrude to be solid (ie: have a color or texture when rendered) it must be created from a closed shape. VW's has always had this requirement, even pre-parasolid.

[michaelk]

Horst

If I remember correctly, I got it to work by slighting changing the path object. I found I had some vertices that were too sharp. I made sure the curves were arcs w/ tangent endpoints and the EAP suddenly got very happy.

Peter, I've had the opposite experience. I often extrude or EAP lines or open polygons and polylines, and have no trouble giving them a fill color or texture.

I find it useful in cases like this where I don't know where the "bottom" of the extrude needs to land yet. I can always go back and fill in the missing side when I figure it out.

michaelk

[Horst M.]

Hallo Peter,

Hallo Michael,

For me it is really cool that you share solutions like above, because somtimes VW is giving me a hard time to come to the result I like to get, because like with the special polygon that Michael created, the EAP works with 3 Stairs, and with 4 it won't...

My experience with VW is, that I never know enough tips and tricks.

Horst M.

[CipesDesign]

Michael, you are correct. I misspoke. What I should have and meant to say was that an object cannot have "none" selected for fill. I just tried open shapes and they seem to work fine, as long as they meet the above criterion. Sorry for the confusion.

[preston bircher designs]

@Pat Stanford Now that I'm on VW2023 >>> Is there any hopes that this has a better answer?  In Spotlight (scenic design) I have an "arch" set piece.  I need a 3" half-round extrusion on the face of the surface (curved arch over a drape)  Is there any hopes in just "extruding along path" with the 3" half-round?  Or to i really have to make it a rectangle, adjust it, change it to a half-round & adjust that?  THX!

[preston bircher designs]

On 11/3/2009 at 12:10 AM, Pat Stanford said:

Limitation in VW.

VW does not like self intersecting objects. When you do the EAP, the profile object is extruded along it's geometric center. Because of the curve in the path, the object intersects with itself.

Assuming that you actually want the "nose" of the risers to follow the path, try the following:

1. Draw a small rectangle and extrude it along the path.

2. Select the riser profile and Copy it.

3. Double click on the extrude and Edit the Profile group.

4. Delete the rectangle from the profile and paste in your riser profile. Move it so that the point you want to travel along the path is located at the 0,0 point of the window. If you don't usually have the rulers turned on, turn them on. It will help you to line things up.

5. Mirror the riser profile so it is to the right of the origin (0,0).

6. Close the polygon so the line between the bottom and top is visible.

7. Click the Exit Profile button and you will have your risers.

@Pat Stanford Now that I'm on VW2023 >>> Is there any hopes that this has a better answer?  In Spotlight (scenic design) I have an "arch" set piece.  I need a 3" half-round extrusion on the face of the surface (curved arch over a drape)  Is there any hopes in just "extruding along path" with the 3" half-round?  Or to i really have to make it a rectangle, adjust it, change it to a half-round & adjust that?  THX!

[Pat Stanford]

Extrude Along Path still runs the initial extrude along the center of the profile object. 

The easiest way is to draw the Path object along your arch and do the extrude, then edit the profile object and move it so that the part of the profile you want to run along the path is at the zero,zero point in the Edit Profile window.

 

HTH