Subject:
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Re: bend thingie creator.
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Newsgroups:
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lugnet.cad.dev
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Date:
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Mon, 27 Nov 2000 23:55:49 GMT
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Viewed:
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1128 times
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koen wrote:
>
> Doesn't this complicate things a lot? It is possible easily draw a hundred
> beziercurves that make up 1 curve, but how do you make 1 equation that
> passes through a hundred points?
Sorry, I explained myself poorly, I divide the curve in segments with
only 2 points each.
Bezier and Hermite curves are very similar, but I don't use Bezier
curves because the control points are not very user-friendly, I'd rather
have tangents and let the user move them with the mouse.
> > I'm using a different solution: I start with a given up vector for the
> > first point and then at each point I calculate the tangent vector (first
> > derivative) and make "side_vector = front_vector x up_vector; up = side
> > x front;" ('x' means cross product) to get the new up vector. Probably
> > not the ideal solution too but it's calculated only once and the results
> > stored in a display list so who cares ? :)
>
> I can calculate the tangent vector too, but just by substracting the current
> point from the next point :-) .
Are you using forward differences to calculate the curve ?
> Your solution sounds a lot faster,sturdier and geekier. I think I'm going to
> steal this idea if I can figure out how to add this up-vector to my
> rotation-matrix.
Just build the matrix with the vectors you have, here's the code I'm
using:
M(0,0) = side[0]; M(0,1) = up[0]; M(0,2) = front[0]; M(0,3) = x;
M(1,0) = side[1]; M(1,1) = up[1]; M(1,2) = front[1]; M(1,3) = y;
M(2,0) = side[2]; M(2,1) = up[2]; M(2,2) = front[2]; M(2,3) = z;
M(3,0) = 0.0; M(3,1) = 0.0; M(3,2) = 0.0; M(3,3) = 1.0;
> > I also added an option to set the axial rotation at each point so you
> > can see the elements twisting, looks very nice on an animation. :)
>
> This definitely sounds very cool, makes me wish I could program a lot
> better.
Feel free to help me with LeoCAD if you have some time to spare. :)
I'm uploading a screenshot of my current curve function to
http://gerf.org/~leo/curve.gif
Next step on my list is to calculate a bounding box and check if the
object created by the curve intersects with a line segment (for mouse
selection).
Does your program have an option to set the exact size of the hose ?
I'll have to add this sometime.
Leonardo
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Message has 1 Reply:
Message is in Reply To:
 | | Re: bend thingie creator.
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| (...) Doesn't this complicate things a lot? It is possible easily draw a hundred beziercurves that make up 1 curve, but how do you make 1 equation that passes through a hundred points? (...) mean (...) segment (...) it (...) with (...) segment in (...) (24 years ago, 26-Nov-00, to lugnet.cad.dev)
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