Locating a point on a curve via distances.. how?

[naughty]

I'm trying to calculate points on a curve at a set distance apart,

e.g. I want to start at curve.u[0] and return the .u value TWO UNITS(cm) ALONG the curve, then FOUR cm along, SIX cm, etc...

My curves are not going to be parametrically uniform and will have differing numbers of spans and min/max values...

Is there an existing command to do this or an easy way without having to rebuild my curves from .u[0] to [1] and then dividing the total arcLen by this...

:nathaN

[naughty]

Never mind folks, I just found it.. you can query the .un[n] values of a curve and it returns the normalised u value...

[EDIT:]

actually no, that's not it... how do I specify say the exact CENTER point of a curve..? or 0.25% along it..?

even with a curve that has a min-max of 0-1, selecting curve1.un[0.5] doesn't give you the middle because of the spans... can anyone help me here...?

:nathaN

[failure]

Create your curves with chord length parametrisation. That way, the parameter value will be equal to the arc length

[joojaa]

Or you can use arc len to find this out by iterating with it.

Anyway theres a even niftier way to do this and its to use the path anim node as it actualy works on percentual distance instead of parametrisation.

[naughty]

yeah, that seems to work, but does that mean I can't do this with curves NOT built using this chord method..?

Is there a rebuild method that'll convert a uniform knot spaced curve to chord length one?

[failure]

I think you cannot rebuild to chord length. It's strange that it isn't included.

You can write a script that will do that by drawing a new chord-length curve from existing curve's cv's.

If you must work with uniform parametrisation use one of the methods suggested by joojaa.

[naughty]

thanks.. that's a decent workround for now..

If you must work with uniform parametrisation use one of the methods suggested by joojaa

If I ever understood what the hell he was talking about I would!

:nathaN

[naughty]

Or you can use arc len to find this out by iterating with it.

how do I iterate with arcLen...? I'm not sure what you mean..

what, and where is a "path anim node"..? do you mean a motionPath node? I'm not sure how I'd use this to get the curve Point info I want. do you have any working examples.. or some pointers (in layman's terms ) to get me started?

:nathaN

[failure]

There already is a script here on highend that does rebuilding to chord len.
Search for "makeChordLength"

[naughty]

yeah, how odd, that script is in our aliasmaya6.0scriptsunsupported folder too...

I just tried it and my original curve has changed noticably... why is it so hard to do something so straightforward sometimes...?

all I want to do is select the mid point of a line!

:nathaN

[failure]

Try with motion path as mentioned earlier:
Create locator and do attach to motion path ( your curve being the motion path ). Now select motionPath node, break default connection for "u value" and set it to 0.5. Locator will now be at the middle of the curve no matter what.

[naughty]

This is all getting very compilcated for such a basic idea... do Alias not think people will want to query distance points on curves..?!?

anyway thanks for all your helpful suggestions but in the end I've just gotten one of our API programmers to write me a plugin that does it..!

:nathaN

[campbell]

yeah, it should be out of the box. and it should also be integrated into snapping - curve halves/quaters/etc and arcLength steps.