# 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
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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.
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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.
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: 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
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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.
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Are the "drag handles" something new to WF2, or are you refering to the control vertices?
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: : > ..... 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? : : ===============================: : :
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