Qualitatively, the Minimum Curvature gridding algorithm for gradient maps is attempting to fit a piece of sheet metal through all of the observations without putting any creases or kinks in the surface. Between the fixed observation points, the sheet bows a bit. The Internal tension is used to control the amount of this bowing on the interior: the higher the tension, the less the bowing. For example, a high tension makes areas between observations look like facets of a gemstone. The Boundary tension controls the amount of bowing on the edges. The range of values for Internal tension and Boundary tension are 0 to 1. By default, the Internal tension and the Boundary tension are set to 0.
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