Digital Map Polyline Simplification via Angle-Threshold Graph Path
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional polyline simplification methods in digital maps can result in angles being reversed or excessively changed, leading to inaccuracies in representing road routes and boundaries, which can cause incorrect directions or 'inside-out' boundaries, reducing the utility of simplified polylines.
Innovation Solution
A method involving the creation of a directed graph with nodes representing potential chords and links between them, where costs are assigned to ensure a least-cost path is chosen that maintains the original polyline's integrity within a specified tolerance, preventing angle reversals and excessive changes by considering chord transitions and nearby objects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If conventional polyline simplification methods are used to reduce the number of shape points, then the data file size and processing time are reduced, but angles may be reversed or excessively changed leading to topological errors
Solution Approach 1:
The patent implements feedback by calculating the angle difference between the original polyline and the simplified polyline at each vertex, and using this feedback to adjust the simplification process. The angle difference is computed and compared against a threshold, and if it exceeds the threshold, the simplification is adjusted to prevent angle reversal or excessive change, thus maintaining topological correctness while still achieving data reduction.
2Quantity of substance
If conventional polyline simplification methods are used to reduce the number of shape points, then the data file size is reduced, but angles may be reversed or excessively changed leading to topological errors
Solution Approach 1:
The patent implements feedback by calculating the angle difference between the original polyline and the simplified polyline at each vertex, and using this feedback to adjust the simplification process. The angle difference is computed and compared against a threshold, and if it exceeds the threshold, the simplification is adjusted to prevent angle reversal or excessive change, thus maintaining topological correctness while still achieving data reduction.
3Device complexity
If maximum deviation distance is used as the sole criterion for simplification, then the simplification process is simple, but angles may be reversed or excessively changed
Solution Approach 1:
The patent combines multiple criteria for polyline simplification: the maximum deviation distance criterion and the angle difference criterion. By using a composite approach that considers both the geometric deviation and the angular change at vertices, the method achieves more accurate angle preservation while maintaining reasonable simplification complexity. The angle difference is calculated and used as an additional constraint alongside the deviation distance.
Data Source
Figure 1
Figure 2
Figure 3
AI summary
Generalization of features in a digital map is enabled by performing a simplificatio of polylines. A set of chords between points on a polyline is selected such that each chord does not violate specified rules such as maximum distance from the original polyline. If a chord is acceptable, a node representing the chord is created, described by the start and en points of the chord. For pairs of nodes created, a transition from the first node to the secon node is evaluated to determine whether it is acceptable. In one embodiment, a transition is acceptable if the absolute value of the angle formed by the chords is within a threshold ang from the angle formed by the original polyline at that point. If the transition is acceptable, link between the two nodes is established. A least-cost path through the graph is chosen, and a simplified polyline is then generated.