Second Derivative
The Grids | Calculate | Calculus directional derivative, Second Derivative, calculates the rate of change of slope along a given direction. Second derivative grid files produce contour maps that show isolines of constant rate of change of slope across the surface. If the slope is uphill, the rate of change is positive and downhill is negative.
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Contour map of original grid file is overlaid on second derivative map. Areas of greatest change in slope in the X direction occur on ridges (light gray) and valleys (dark gray). |
The directional second derivative is the directional derivative of the first directional derivative:
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The compass-based grid notation difference equation used in Surfer takes the form:
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