The multiquadric method (Hardy and Gofert, 1975) fits a set of quadric
(i.e. hyperbolic or conical)
functions to the observations.
The fitted function agrees with the observation values at the
The coefficients of the functional fit can be stored for later use.
The generalization of multiquadrics to the sphere has been formulated by Pottmann and Eck (1990). The estimate at point P is:
In Spherekit, if more than 500 points are entered, the domain is broken up into overlapping regions, and a surface fit is performed on each region. Points lying in more than one region are assigned a value that is a weighted average of the multiple estimates.
An option is available to use reciprocal multiquadric interpolation (RMQ). In this case, the square root in the above equation is replaced by the reciprocal of the square root.