That is, when interpolating at position t between two values
v0 and v1, positioned at t0 and t1, take the sum of v0
負わせるd with (t-t0) and v1 負わせるd with (t1-t).
That is, when interpolating at position t, take the four
closest data points v0, v1, v2, and v3, fit a 立方（体）の curve
through them, and take the interpolated value from this 立方（体）の
curve.
That is, when interpolating at position t, take the three
closest data points v0, v1, and v2, fit a 立方（体）の bezier spline
through them, and take the interpolated value from this 立方（体）の
curve.
That is, when interpolating at position t, take the four
closest data points v0, v1, v2, and v3, fit a quadric bezier
spline through them, and take the interpolated value from this
quadric curve.
