Method for applying clothoid curve values to roadways in a geographic data information system

1. A method for applying clothoid curve values to roadways in a geographic data information system, comprising:

selecting database segments in the geographic data information system, wherein the database segments describe roadways;

determining segment chains from the selected database segments, wherein determining the segment chains comprises:

identifying a plurality of at grade junctions of the selected segments and all dead ends of the selected segments as important locations; and

finding each geographic chain of segments that traverse from any such important location, and touch no other such important location, until reaching the same or other such important location;

preparing the segment chains for transition to curvature space;

transitioning to a curvature function in the curvature space, by computing heading change at points along the segment chains, resulting in a transformation of the segment chains into clothoids;

smoothing the curvature function;

fitting the smoothed curvature function with a more generalized form which remains within a selected tolerance of the smoothed curvature function; and

storing parametric values of the smoothed curvature function for the segment chains in the geographic data information system;

wherein the more generalized form of the smoothed curvature function is obtained by recursively applying a regression technique to said smoothed curvature function and seaming together the resulting plurality of regression-fit functions into a piecewise linear function, said seaming being achieved by assigning a common value to the more generalized form of the smoothed curvature function at the point where successive regression-fit functions are seamed together.

2. The method of claim 1 , wherein preparing the segment chains for transition to curvature space further comprises finding corner interfaces.

3. The method of claim 2 , wherein finding corner interfaces incorporates shape generalization to remove nearly collinear shape points.

4. The method of claim 2 , wherein finding corner interfaces comprises:

using relative accuracy information to approximate a line attached to a curve defined by three successive shape points.

5. The method of claim 2 , wherein preparing the segment chains for transition to curvature space further comprises:

generalization of shape points that have not been identified as part of a corner interface.

6. The method of claim 1 , wherein preparing the segment chains for transition to curvature space comprises:

determination of each segment chain's geographic context.

7. The method of claim 1 , wherein smoothing the curvature function comprises Gaussian smoothing.

8. The method of claim 1 , wherein smoothing the curvature function comprises:

an approximation to Gaussian smoothing with a piecewise linear function connecting Gaussian sample points placed at intervals from shape points.

9. The method of claim 8 , wherein the approximation to Gaussian smoothing is obtained from iterative samples stored in a table that associates Gaussian intervals with numeric parameters.

10. The method of claim 1 , wherein the regression-fit functions are weighted least squares regression fit functions.

11. The method of claim 10 , wherein fitting the smoothed curvature function further comprises:

applying a search for acceptable straight line substitutions to the piecewise linear fit function.