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Loft problem
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These pages are a copy of the official truespace forums prior to their removal somewhere around 2011.
They are retained here for archive purposes only.
Loft problem // New Users
Post by LongWolf // Feb 5, 2009, 7:00am
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LongWolf
Total Posts: 62
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I seem to have found a problem with the loft tool.
I was making a spring to hold a chair back to a stool.
Drew a line (changed to red for viewing), added a 3x0.25 rectangle to it and used Loft.
When you look at the bottom, rendered image you can see some twist.
But if you look at the back view, you can definitely see the twist.
Did I do something wrong? |
Post by spacekdet // Feb 5, 2009, 8:13am
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spacekdet
Total Posts: 1360
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Cool!
I'd check the control point indicated below for any skewing of the handles.
You might need to tweak it or possibly add another point or two on either side nearby to ease in and ease out of the sharp change in direction.
18038
Your other option would be to draw the side profile of the spring-basically make the rail curve a closed one- and then loft or convert to poly and sweep that. |
Post by LongWolf // Feb 5, 2009, 9:19am
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LongWolf
Total Posts: 62
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Cool!
How so, did I find a legit bug? :)
Here's a pic of the handles (before playing with things).
Tried adding two points then deleting the point you marked also tried messing with the point on the opposite side of the curve.
Things only got worse.
I've put the spring shape and rectangle lines in the following zip file, if you want to try it out. |
Post by spacekdet // Feb 5, 2009, 10:36am
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spacekdet
Total Posts: 1360
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I'm getting the same results as you, but I don't know why.
It may indeed be a bug, put a feather in your cap!
A couple questions:
the rectangle looks a little skewed...did you lay it out in a top view with grid snap on and then rotate it into place?
How did you construct the other curve?
I tried changing all curve point parameters to sharp before I lofted, it seemed to help a little but then I scaled the lofted shape up to see better, the rectangle would 'rock' back and forth and end up skewing. Very strange.
I still think you should just go with Plan B, complete the rail curve as a closed shape and loft/sweep it.
You should be able to achieve the rounded portion with a lot fewer control points. |
Post by LongWolf // Feb 5, 2009, 11:36am
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LongWolf
Total Posts: 62
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For the rectangle, I created the draw panel in the correct orientation, i.e. no rotating.
Then set the scale to inches, used the Add Polyline tool to mark the 4 corners, used Close Curve and then used the Object Info window to set the exact height and width.
For the shape line, I started with a circle, broke it, deleted a few points, moved the end points and adjusted the angles.
The shape is drawn on the x/z plane so all points and handle points should have the same y value.
Checked them all and they where good on the y.
But the handles on the horizontal section where very slightly off on the z axis.
So I fixed that and tried again.
Now it twists the other way and has a crimp :D
I'd hate to have to try closing the shape so it could be sweeped, but you may be right. |
Post by SteveBe // Feb 5, 2009, 9:24pm
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SteveBe
Total Posts: 282
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You might want to try Clintons NURB plug-ins: http://www.clintons3d.com/truespace/nurbs/nurbs.html
The Weld Curve plug may help with this, I tried an 1/2 circle arc and 2 poly lines
and they worked, tS's curve drawing tools are not the best and I've always
preferred a vector program to create the curves and import into tS. |
Post by LongWolf // Feb 6, 2009, 5:55am
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LongWolf
Total Posts: 62
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Hi Steve,
I looked at your picture and noticed that you lofted to a line instead of a rectangle.
For the heck of it, I tried only using a line with my shape curve.
It worked fine with no twist.
But that's not really a 3d object is it?
I downloaded your cob file, but you'd already lofted it.
If you have time, and still have your original shape curve, you might try lofting to a rectangle to see what happens.
In the mean time, I went ahead and closed my shape curve then used extrude.
In order to sweep the obj, it had to be converted to a polyhedron.
That gave it a whole lot of un-needed vertexes.
I spent over an hour removing the un-needed ones!
P.S. spacekdet, I took your advice and removed half the control points before using extrude. |
Post by TomG // Feb 6, 2009, 6:46am
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TomG
Total Posts: 3397
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Removing unnecessary vertices and edges can often be accomplished this way - create a cube not touching your original object; select your original object that needs unnecessary vertices / edges removing; right click boolean subtract on the Model side and ensure "Delete Edges" is enabled; using boolean subtract, subtract the non-touching cube from the original object.
Any edges that are not required to maintain geometry will be removed (eg if a face on a cube was triangulated). Edges that remain are needed to ensure that all faces have co-planar vertices (ie that all faces are flat). If a face is flat without those extra edges, they will be deleted automatically.
HTH!
Tom |
Post by Nez // Feb 6, 2009, 7:50am
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Nez
Total Posts: 1102
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I have to confess, for that shape I'd have simply formed two cuboids and a pair of cylinders, subtracting the smaller cylinder from the bigger to get a tube of appropriate thickness and then sliced half the tube off with another subtract and assembled all the bits.... |
Post by spacekdet // Feb 6, 2009, 8:37am
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spacekdet
Total Posts: 1360
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Yep, I would have converted the closed curve to a polygon while it was still 2D, and then swept it. I probably should have been a little more specific on that step.
You ended up with a lot more polygons than needed probably because you lofted it first and then converted to poly- the conversion process can be a little extravagant with the number of polygons it creates in a 3D object.
There's a little more control if you start out with a 2D shape and sweep it yourself. |
Post by LongWolf // Feb 6, 2009, 10:26am
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LongWolf
Total Posts: 62
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Did some more tests.
test 1
Taking the closed curve shape, extruding and sweeping gave 321 vertexes and 542 faces.
test2
Converting the curve to polygon and then sweeping it gave 108 vertexes and 56 faces.
test3
But, using Toms trick on the 321 vertex obj took it down to 76 vertexes and 39 faces.
Out of the 76, 12 were not needed so it ended up with 64 vertexes and 33 faces.
Thx for the tip Tom! |
Post by SteveBe // Feb 6, 2009, 6:42pm
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SteveBe
Total Posts: 282
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For this kind of shape I wouldn't use NURBS unless I wanted to keep the object as a solid.
Attached video shows how this can be done in approx. 1 minute with the workspace poly tools. |
Post by LongWolf // Feb 7, 2009, 7:54am
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LongWolf
Total Posts: 62
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Thx Steve,
Maybe someday I'll get as fast as y'all :) |
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