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Thursday, March 20, 2008

OP of the day ! the SPLINE VOP

in my thirst for knowledge, ill attempt to write a lil bit about a SOP or OP here and there.
Theres ALOT of ops in H9...so it could take a while. i counted 124 COPS alone !)
ill probably skip over the easier ones...and look toward learning new stuff.

so to break the ice have randomly chosen to look at the spline COP.
ok this one seems tricky because i dont have the math of splines in me...but i get the impression you define a type of spline and give it some input points - then it can retun a nice smoothly interpolated point for you.

so in the simplest example if you gave it two points 0 and 1 and then asked for the midpoint - obviously it would give you .5. This could be handy if you specified interpolation on a nice smooth spline where the point positions aren't so easy to calculate.

the help file refers me to the FIRE VOP example which generates 2D fire by blending some colors.

It talks about Cardinal Splines vs Linear...so i looked into this.
the maths here is a bit full on for me. but a useful link if your into splines and how to plot them.

www.ibiblio.org/e-notes/Splines/Intro.htm

at last something i can read ! from the Microsoft Developer network
(i f you believe anything from MS)

"A cardinal spline is a sequence of individual curves joined to form a larger curve.
The spline is specified by an array of points and a tension parameter. A cardinal spline passes smoothly through each point in the array; there are no sharp corners and no abrupt changes in the tightness of the curve. "

hers some cool java interactive spline demos...or you could just open Houdini :)
www.cs.uu.nl/docs/vakken/ddm/curvedemos.htm

unrelated bbut googling led me to this page with some XSI rigging effots
www.matkovic.com

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any how - lets look at the FIRE VOP.
cool !
where in hot hell is a spline used here ? - i see - the color ramp VOP is actually a spline VOP that has been renamed to suit its purpose better as there are several colors that make up the 2D fire being blended together. The interpolation bewteen colours can be a cardinal spline or linear interpolation. the results change visually...and this means more to me as i am more of a visual person :)


On the left is linear interpolation and on the right cardinal spline interpolation. There are some others but i have ignored these as they are related to RSL - renderman shader language...
and i havnt gotten in to those depths yet...

as black is one of the colours or points on the slpine - the flames appear taller in the cardinal pic, as they are being interpolated differently - lust like motion is interpolated differently in a motion graph - if your an animator. hmmm interesting. but how can i use it...maybe a post for another day.

next VOP....stone !
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