Graphics cubic splines

Figure 1 graphically depicts the numerical data relevant to our application listed by Lundberg et al. Different sets of curves off vs. X are provided for individual values of d /d0. Discrete data were provided in the numerical tables of the original work to produce the continuous traces in Figure 1, a cubic spline fitting was used. 

A schematic of the coordinate system fixed to the LV chamber is shown in Figure 3. After the transformation of the cardiac outlines to the LV-fixed coordinate system, each of the short-axis contours is displayed on the screen of the graphics terminal with a predefined number of radial divisions emanating from the center of the cross-section as shown in Figure 4. The intersection points between the radial lines and the cardiac contours (endo- and epicardium) are selected as the nodal points. Once the Xand Y coordinates of the nodal points are known, the corresponding Z coordinates are evaluated from the equation of the plane of the short-axis images. A least square or cubic spline curve is fitted... 

A simple inspection shows that cubic functions (splines) shown graphically in Figure 2.5 satisfy the above conditions. 

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