How to create workpoints defining equal-length segments of a spline?

[Anonymous]

I want to build a space-frame by taking a lofted surface and sub-dividing it into equal segments.
My idea is to create a slider that allows me to dynamically increase and decrease the amount of segments along each rail and profile of the surface, basically changing the segmentation in either the U direction or V direction of the surface.

With segments defined, I'll then try to create workpoints at each segment connection point, and that will be repeated on an offset surface which has the segments offset by 0.5 the segment length, in order to produce the triangulated members that connect between upper chords and lower chords of the space-frame.

The workpoints are needed for assembly constraints. The actual frame members could be generated from an iPart which creates or deletes children depending on the segmentation values currently set in the slider, and updates the length parameter of each child to suit the space-frame segmentation.

Any help is greatly appreciated!

Santiago

[Anonymous]

If you have a spline you can use its CurveEvaluator object to do what you
want. First, you can use the evaluator to determine the length of the
curve. Then you can use the evaluator to find points along the curve at a
specified distance from a point as measured along the curve. You may need
to convert between parametric and model space, but this is also supported by
the CurveEvaluator object.
--
Brian Ekins
Autodesk Inventor API Product Designer
http://blogs.autodesk.com/modthemachine

[Anonymous]

Thanks Brian,

Here's another question for the same program.
I have two 3D Sketch Points.
I have created a function for each X, Y and Z, which I use to create 3D Sketch Points that are used to create a 3D Spline which approximates an arc (with a given radius and center).

I want to change the functions so that the arc is drawn with a given radius which starts at one of the 3D Sketch Points and ends at the other 3D Sketch Point.

I also need the arc to be a spline which is in the 3D Sketch, because I'll need to modify it in X, Y and Z. In other words it's created to approximate a 2D arc but can be manipulated in 3D.


I guess this might be more math-related than Inventor API-related.
Would you happen to know how to create that arc?
How does AutoCAD draw an arc based on 2 points and a radius??

I'm sure I'll get to it eventually (I'm trying to remember analytic geometry, etc), but any insight will help alot.

Santiago

Edited by: SantiagoDiaz on Oct 22, 2009 2:39 PM Edited by: SantiagoDiaz on Oct 22, 2009 2:42 PM

[Anonymous]

Unless you really need a spline for some reason, I would suggest creating an
arc instead. For a 3D sketch, the SketchArcs3D collection support several
methods for creating an arc. Which one to use depends on the kind of
information you already have. Two points and a radius isn't enough
information to fully a 3D arc. You need something else to define the plane
that the arc will lie on. Then it's time to see if you can compute enough
information to be able to use one of the Add methods. I know this probably
isn't that much help but I don't have enough information about your problem
to be more specific.
--
Brian Ekins
Autodesk Inventor API Product Designer
http://blogs.autodesk.com/modthemachine