An apparatus accesses terrain data describing a surface and comprising a plurality of positions located on the surface. The apparatus determines curvatures/second derivatives of the surface between adjacent positions along surface spanning lines along the surface. The apparatus defines vertices by determining an accumulated absolute curvature along the line spanning the surface based on the curvature between positions by adding the absolute value of the curvature to the accumulated absolute curvature, determining whether the accumulated absolute curvature is equal to or greater than a reset value, and when it is determined that the accumulated absolute curvature is equal to or greater than the reset value, defining a vertex at the position. When it is determined that the accumulated absolute curvature is not equal to or greater than the reset value, the absolute value of the next curvature is added to the accumulated absolute curvature.
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