Database for efficient storage of track geometry and feature locations
A database schema is disclosed that can significantly reduce the quantity of data required to describe the geometry of a train track and the geo-locations of features (e.g., grade crossings, mileposts, signals, platforms, switches, spurs, etc.) along the track. In accordance with the illustrative embodiment, a railroad track is represented as a plurality of partitions, each of which has its geometry contained within unique track point elements. Multiple track partitions are then joined together by common track point elements at their boundaries to create continuous rail networks. A compact table schema is employed that enables continuous sections of three-dimensional track splines to be rendered accurately in the track database, irrespective of the location of vertical and horizontal curvature along track segments. The data representation scheme also enables efficient storage of the geo-locations of features along a track, as well as the direct reconstitution of accurate three-dimensional track splines.
1. A method for operating a train on a train track according to a smaller-size database that captures the geometry of the train track, the method comprising:
obtaining a set of geo-locations from a survey of the train track, wherein each geo-location is a point on the centerline of the train track, and wherein a first database comprises the obtained set of centerline geo-locations;
converting the centerline geo-locations from latitude/longitude/altitude to a set of points expressed in three-dimensional Earth-Centered Earth-Fixed Cartesian coordinates;
generating, by a data-processing system, based on the three-dimensional coordinates of the set of points, a piecewise polynomial spline that is defined in terms of a proper subset of the set of points;
populating, by the data-processing system, a first data structure in a second database, wherein the first data structure stores for each point P in the subset of the piecewise polynomial spline:
(i) the three-dimensional Earth-Centered Earth-Fixed Cartesian coordinates of the point P,
(ii) an estimate of the heading of the train track at the point P,
(iii) an estimate of the grade of the train track at the point P, and
(iv) an estimate of the curvature of the train track at the point P;
populating, by the data-processing system, a second data structure in the second database, wherein the second data structure stores for each of a non-empty set of features along the train track:
(i) an indicium of a point in the subset of the piecewise polynomial spline, and
(ii) an offset from the point to the feature;
wherein the second database comprises a smaller quantity of data than the first database; and
operating the train on the train track according to the second database.
2. The method of claim 1 further comprising conditioning the set of centerline geo-locations to ensure the absence of direction reversals and discontinuities.
3. The method of claim 1 wherein the first data structure identifies one of the points in the subset as the first point, and wherein the data-processing system further populates the first data structure for each point P in the subset with an offset from the first point.
4. The method of claim 1 wherein the first data structure and the second data structure are lists stored in respective files in the second database.
5. The method of claim 1 wherein at least one of the features is a station.
6. The method of claim 1 wherein at least one of the features is a grade crossing.
7. The method of claim 1 wherein a data store comprises the first data structure and the second data structure.
8. The method of claim 1 wherein the second data structure represents the locations of the non-empty set of features along the train track.
9. The method of claim 1 further comprising:
deriving, by the data-processing system, the exact location of a feature in the non-empty set of features from the piecewise polynomial spline and corresponding entries in the second data structure.