Digital map editing process using active contour manipulation
A method for realigning network elements in a digital map based on a new data set using active contour manipulation techniques. The active contour optimization process is controlled so that certain desirable features in the original shape of the active contour(s) are not distorted. In the case of network features which may be represented by two or more open active contours, the active contours are coupled prior to optimizing so that the original desirable shape, e.g., the parallel spacing of lanes in a dual carriageway road, may be maintained during the optimization process. In the case of certain closed active contours, for example roundabout geometries, a single closed active contour may be coupled to itself by linking its control points one-to-another and maintaining a proportional direction and distance movement during the optimizing process. As a result, data base networks can be assessed and aligned with less difficulty and geometric distortion.
1. A method for improving a digital map using active contour manipulation techniques, said method comprising the steps of:
providing a digital map corresponding to a region of land in reality, the digital map having at least one network element corresponding to a feature in reality;
providing a new data set corresponding to the same feature in reality as the network element;
treating one of the network and the new data set as a source geometry having at least first and second active contours spaced apart one from the other and forming a relative shape therebetween, while treating the other of the network and the new data set as an external energy source;
assigning internal and external energy values to each of the first and second active contours, and assigning a velocity field to the external energy source; and
coupling the first active contour to the second active contour while simultaneously optimizing the positions of the first and second active contours relative to the external energy source using an active contour manipulation strategy wherein the positions of the first and second active contours relative to the external energy source are together iteratively adjusted to more desired positions by trying to lower their respective internal energies in relation to the external energy source without changing the relative shape between the first and second active contours during the said optimizing process.
2. The method of claim 1 wherein each of the first and second active contours include a plurality of control points spaced therealong, said coupling step including linking a control point in the first active contour with a corresponding control point in the second active contour and further including proportionally moving the linked control points in direction and distance during the respective said optimizing steps.
3. The method of claim 2 wherein said step of proportionally moving the linked control points includes maintaining a constant distance between the linked control points throughout said step of simultaneously optimizing the positions of the first and second active contours.
4. The method according to claim 1 wherein said step of providing a new data set includes collecting probe data from a plurality of probes, each probe developing a respective probe trace comprising a sequence of discrete time-stamped probe positions plotted relative to the digital map.
5. The method according to claim 1 wherein said step of providing a new data set includes providing a secondary digital map network.
6. The method according to claim 1 wherein said step of providing a new data set includes providing generally parallel first and second active contours corresponding to a dual carriageway road feature.
7. The method according to claim 1 wherein said step of providing a new data set includes providing generally arcuate first and second active contours corresponding to a roundabout road feature.
8. The method according to claim 1 wherein said step of assigning internal and external energy values includes assigning equal energy values to the first and second active contours.
9. The method according to claim 1 wherein said step of assigning a velocity field includes drawing probe traces on raster images and then using the resulting gradient values between pixels as the assigned velocity field.
10. The method according to claim 1 wherein said step of assigning a velocity field includes creating raster images from another network geometry and then using the resulting gradient values between pixels as the assigned velocity field.
11. A method for re-aligning network elements in a digital map using active contour manipulation techniques, said method comprising the steps of:
providing a digital map corresponding to a region of land in reality, the digital map having at least one network element corresponding to a feature in reality;
providing a new data set corresponding to the same feature in reality as the network element;
treating one of the network and the new data set as a source geometry having at least one closed active contour forming an original relative shape, the closed active contour including a plurality of control points spaced thereabout;
treating the other of the network and the new data set as an external energy source;
assigning internal and external energy values to the closed active contour, and assigning a velocity field to the external energy source; and
coupling each control point in the closed active contour to another control point in the closed active contour while simultaneously optimizing the position of the closed active contour relative to the external energy source using an active contour manipulation strategy wherein the position of the closed active contour relative to the external energy source is iteratively adjusted to a more desired position without changing the original relative shape within the closed active contour during the said optimizing process.
12. The method of claim 11 wherein said coupling step includes linking at least two control points and moving the linked control points in unison during said optimizing step.
13. The method of claim 11 wherein said step of providing a new data set includes collecting probe data from a plurality of probes, each probe developing a respective probe trace comprising a sequence of discrete time-stamped probe positions plotted relative to the digital map.
14. The method of claim 11 wherein said step of providing a new data set includes providing a secondary digital map network.