controlling*length* of tangent of a 3d datum curve

hi all,

I usually create surface models using datum points and datum curves
through points subsequently creating boundary blends using these.
I can control the tangeny (and the curvature) by creating tangent vectors.
But now I would like to know wether I can control the *length* of the
tangent.
Is that at all possible?
wzzl

 

............ But now I would like to know wether I can

You can expose the control vertices and tweak the tangent weight if it's a
two point spline (datum and sketcher). Can't if there are internal fit
points, though.

A couple of ways to do what I think you're after:

_ Create the foundation curve.
_ Trim the ends back an appropriate amount.
_ Create two point curves to replace the trimmed ends,
applying G1 and / or G2 end conditions and tweak (G1 only).
_ Create an approximate composite copy of the three curves.

--- or ----

Create the curve as the intersection of two surfaces. The advantage is that
you can (unlike the spline) use multiple sections for a Boundary Blend and
still specify tangent (or curvature) weights.

=======================

 

: hi all,
:
: I usually create surface models using datum points and datum curves
: through points subsequently creating boundary blends using these.
: I can control the tangeny (and the curvature) by creating tangent vectors.
: But now I would like to know wether I can control the *length* of the
: tangent.
: Is that at all possible?
: wzzl

You always could do it with ISDX. Now Wildfire has this ability, as well. It
throws in an arbitray length which you can adjust and it even has drag handles for
the adjusting the tangency length.

Previous versions had something called 'Tweak', functionality down toward the
bottom of the Menu Manager list of functions. With a curve through only two points
and only end point tangency governing the shape of the curve, it would give you
control points and a control poly for adjusting the shape. The only direct way
though was adding curvature to the surface tangent end point condition. And you
would only get that check box after you'd set both start and end point tangency to
surface tangent. Checking the 'curvature' box would change the length of the
tangency.

David Janes

 

Minor correction, if I may. 8~)

Checking Curvature sets a curvature continous end condition (G2 or C2,
depending on terminology used). There's a difference.

--------------------------

Are the "drag handles" something new to WF2, or are you refering to the
control vertices?

================================

 

:
: > ..... Checking the 'curvature' box would change
: > the length of the tangency.
:
: Minor correction, if I may. 8~)
:
: Checking Curvature sets a curvature continous end condition (G2 or C2,
: depending on terminology used). There's a difference.
:
You're right, I should have said 'effectively' or 'apparently', as this does
change the shape of the curve, shown by curve analysis, at the boundaries. I was
thinking that wzzl might have been after making the tangency better, not just
longer.

DJ
: --------------------------
:
: Are the "drag handles" something new to WF2, or are you refering to the
: control vertices?
:
: ================================
:
:
: