TPC can smooth contours lines, replacing the abrubt angles found in Engineering contours with arcs that 'smooth' out the contour lines.
By default, contour lines are drawn as straight lines from triangle edge to triangle edge. If the contour direction changes at a triangle an angle is formed. Thses are called Engineering Contours and are the default type of contour that TPC creates. Engineering contours are acurate in that they always cross through the grade points on the triangle edges and do not attempt to model what happens between the triangle edges.
Engineering contours are the fastester than smoothed contours because they require fewer computations.
Contour smoothing replaces the angles formed where a contour line crosses a TIN line (triangle edge) with either an arc or a spline. There are several methods that can be use, each with their own advantages.
TPC smoothes contours by replacing the angles where the contour line changes direction with a short arc that passes through the same grade point on the edge that the Engineering contour line would have passed through. This produces a smoothed contour that is accurate as an Engineering contour at the edge. By definition, if the replacing arc passes through the same grade point, the contour line between edges must be displaced to one side or the other in order to form a tangent arc at the edge. TPC calls this possible displacement 'Tension'. If you smooth contours with a tension of 1.0 (the default), a contour line is allowed to be displaced up to one contour interval. A Tension of 0.5 would allow a contour line to be displaced up to half of a contour interval. The Tension therefore, determines the radius of each arc that replaces an angle.
Contour smoothing also lets you specify a maximum interior angle at which smoothing will be applied. An angle of 180 degrees would indicate that the contour direction does not change. An angle of 170 degrees (the default) would indicate that if a contour line changes direction less than 10 degrees at an edge,don't apply smoothing at that angle.
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