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Catmull Rom splines, scaling the input.

  1. Jan 20, 2010 #1
    Hi. I've tried doing some camull-rom interpolation for the following data.
    x y
    0.2 1.221402861
    0.3 1.349864712
    0.4 1.491929555
    0.5 1.649697833
    0.6 1.828165418
    0.7 2.042000232
    0.8 2.332915111
    0.9 2.808281551
    1 3.718281828
    1.1 5.597908484
    1.2 9.511853345
    1.3 17.45514585
    1.4 32.98066546
    1.5 62.14672813
    1.6 114.9041952
    1.7 207.0733374
    1.8 363.0963701
    1.9 619.7925202
    2 1031.389056

    I chose to interpolate for point 1.1 (i'm assuming this point is non-existent).
    I am using the following method:

    f(x) = [1, x, x^2, x^3] * M * [p0, p1, p2, p3]

    And M is the matrix,

    0.0 1.0 0.0 1.0
    -0.5 0.0 0.5 0.0
    1.0 -2.5 2.0 -0.5
    -0.5 1.5 -1.5 0.5

    The "tension" value (greek letter tau) is 0.5.

    Thus, the 4 points chosen were 0.9, 1, (2 before 1.1), 1.2, 1.3 (the 2 after 1.1).

    I did it in matlab and got wrong values (using an input of 1.1 and expecting to get a value close to 5.5979). I have since learnt that the input needs to be between 0 and 1. How do I scale this value of 1.1 to be between 0 and 1 ? And does anything else change , in the M matrix, matrix of points [p0, p1, p2, p3] ?

    Thankyou.
     
  2. jcsd
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