Each Interpolation has it's own equation (linear, quadratic in,
sinusiodal in-out, etc etc)
For linear, the general equation (using x and y since they're
familiar) is:
y= a.x + c
For your range mapping [0,1] —> [-1,1], simultaneous equations can
quickly tell us the values of a and c:
When x=0, y=-1 ∴ c= -1 ie, y= a.x -1
For x=1, y=1 so substituting into y= a.x -1,
1 = a*1 -1
⇔ a=2
So your equation for linear mapping of [0,1] —> [-1,1]
is y = 2.x -1,
Test our formula for x=0.5,
y = 2*0.5 -1
= 0 ✔ It checks out ok!
Other general equations to use:
y = a(x+b)² +c [Quadratic] or
y = a.x² +b.x + c or
y = (x+a)(x+b) + c (Fixed the Typo present in the version I sent
you earlier Oscar)
y = a.sin(x+b) +c [Sinusoidal]
y = cb(x+a) + d [Exponential] or
y = a.exp(x+b) + c
y = a.x³ + b.x² + c.x +d [cubic]
Solving some of these equations can be a bit more involved but mostly
not to difficult by substituting in your range limits and mid-point or
whatever. These should work for In-Out. In cases of just In or just
Out you'll need two equations. One being say quadratic the other
linear. Then switch from one equation to the other depending if x is <
or ≥ the crossover point. I find Apples Grapher app (Utilities
Folder) helps to visualise these equations. Many resources via
wikipedia too.
Hope that helps
Alastair
On 04/01/2011, at 9:03 PM, Oscar 'offonoll' wrote:
Hello and happy new year!
I am wondering what is the Interpolation mathematical equation. as I
normaly use it to transform a range of 0-1 (position) to my personal
range such as -1 to 1.
thank you!!
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