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Extrude along Path Rotation

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Modeling Question.


Why does extrude along path randomly rotate my profile curve? 


I can't seem to keep my profile in the same orientation as desired.  No matter which boxes I check.  Selecting Fix Profile seems to send the extrusion randomly out of position.  Selecting Lock profile plane seems to not do much of anything besides create a random error message or distort the extrusion. Is this a feature of the program, or am I missing something?




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If the Lock Profile Plane and Fix Profile are not checked, Vectorworks places the profile center at start point of the path.  The profile is also oriented so that it's plane is Normal (perpendicular in 3space) to the path at the start point of the path.  For example, a rectangle profile drawn on any plane, anywhere in the drawing, and a straight line path starting at 0,0,0 extending along the  x axis of the ground plane will result in an EAP with the profile "standing up" on the y,z plane with center of rectangle at 0,0,0.  Curved paths may have twist along their length causing the Normal to change. eg a non planar NURBS curve with start point on the layer plane, will have a Normal at the start point that is not necessarily perpendicular to the layer plane and which changes along the path.


The fix for rotated profile and for placement of the profile relative to the start point of the EAP is to edit the Profile:

Right Click the EAP>Edit Profile>if needed adjust view to select and look at the plane of the profile object> Rotate 90º, then move/drag until the desired point of the profile is at the cross hair (represents the start point of the path).


If the path and profile are arranged as desired prior to the EAP, try the Fix Profile option. (eg if the profile is "standing up" relative to the path, and a corner of the profile is placed at start of path and the intent is to have that corner stay on the path along the EAP). Note, this also affects how the profile twists and tilts as it progresses along the path.  Results may vary from expectations. Lock Profile Plane keeps the profile plane parallel to starting plane as profile moves along the path, but the profile still rotates in plane responding to twist in the path.  Results may differ from expectations until some experience is gained.


I never did figure out why my profile often rotates from my drawn orientation.  Probably the direction I choose when drawing the paths and profiles. Or some kind of vwx front/back view convention contrary to my understanding.






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Benson's explanation is intriguing, but I think it went over my head a bit.  I'll have delve into those options further.  It would be helpful if NNA would provide a precise mathematical explanation of the various checkbox options.  The explanations in the help manual are intended to be understandable, but they sacrifice precision in favor of over-simplification.


cberg, it looks to me like your specific problem is that the shape of the extrude is rotated 90 d from what you intended.  The easy fix for that would be to edit the profile (right click the extrude object and chose edit profile instead of edit path).  Then rotate your shape 90 d.  I don't think the extrude along path command is necessarily aware of the relative orientation of your extrude shape, so it is picking an orientation based on its own logic instead of what seems to you to be your obvious intention.

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The math of those EAP options seems somewhate unexplained to me, too. It makes sense at the start of the extrude, but how it responds through to the end is not always clear.

I think an option a lot of us want is for the profile to stay parallel to ground plane throughout  a curving extrude, ie, does not respond to the twist.


A note about twist - we experience this with real materials, such as garden hoses and electrical extension cords, especially noticeable if the cord has a colored stripe along the length.  If the cord is arranged with loops or curves that are not all in same plane, the stripe will not face same direction along the curves - it twists.


My examples are 4 versions of the same profile extruded along the same path.  My extrudes are superimposed to show differences in the options.  Try same by drawing a profile and a curving path. Repeat with the different options checked. Assign different fill colors.


Superimposed is helpful. Delete/undo or move the EAPs to compare the options and better understand the options. 


On big takeaway is that the Fix Profile button preserves the orientation (stays in its plane) of the profile at start of the EAP.





Edited by Benson Shaw
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Fix Profile is the option to know about. For it to work you need to have already placed your profile in 3d space in relation to your path object. This means your profile needs to be a 3d object (usually a NURBS curve) or a planar object arranged in 3d space. Your profile cannot be a screen plane object.


In early versions of VW (Minicad) you would most often create an EAP with a 2d screen plane profile and VW would auto-orient the profile to the path. If you leave the "Fix Profile" checkbox unchecked VW will still do this. Often this method will require editing the profile portion of an EAP and repositioning the profile with respect to the profile origin.




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Benson, Kevin, thanks - those are very helpful.  NNA should hire you to help write the manual!  I think there are mathematical definitions that would help those who care about what is going on understand.  I.e., NNA should define a normal to a profile shape (some people understand that, some may not), define the relationship between that normal and the path or spatial axes (only the software designers are likely aware of these).

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@PRetondo - Plus one for requesting some deeper explaining from the mother ship.  I would also agree that most users don't really care about the deep geometry explanation, but rather want some guidance or examples to help predict the outcome of various options, or achieve a desired representation.


I think users of Vectorworks should adopt an attitude of testing in a simplified environment (new blank file, only a few objects) - try the options of the various functions of the tool/command to explore, learn or relearn functions and outcomes of the various modes and options.  This formerly easy to learn program (at least I picked it up fairly easily) is now a sprawling, constantly upgrading, detail laden enterprise with so many specialized modules, tools, modes and commands that thorough knowledge is near impossible to attain or retain. Not a bad thing, but users need awareness and attitude of constant learning.


@Kevin McAllister- You are right (as usual!) unless the path swerves around in 3 space (3 axis twist). The Lock Profile Plane option does affect the progression of the extrude whether or not Fix Profile is enabled.  See the superimposed pink (not locked) and gold (locked) pair in earlier post. The extrude twists in both options, but differently. The locked profile (gold) remains parallel to its start plane (not the plane it was drawn on, but rather the normal plane at start of path). Maybe mathematically the Lock Profile Plane defeats or locks one axis of the normal-to-path twist? A planar path would have only a 2 axis twist, so the Lock Profile Plane might lock the inactive twist axis and result in same extrude as unlocked?


But my attempts to deconstruct & describe the EAP, normals, twist, etc are not really relevant, and are possibly wrong!  The important thing is for a user to find an option that properly represents the intended extrude. TEST!


@ChubbyChecker - sorry.



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Thanks all for helping to explain this rather complex taxonomy of Extrude Along Path options! 


I wound up converting all the curves to NURBS and lofting with one rail.  Still a few too many steps for something that should be rather simple, and I had to move resultant shape into place after lofting.  That said, I will freely admit that I do not understand the complexity of math/programming under the hood.


For comparison/reference, the "Sweep 1" function in Rhino seems to do this effortlessly/seamlessly.  No need to position or rotate the profile shape relative to the path.  It just works. :-)  I understand that VW is a vastly different software ecosystem, but it always helps to understand how other folks are tackling this problem.


Thanks again for all your help.




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