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SpaceNet Road Detection and Routing Challenge Part II — APLS Implementation

Adam Van Etten
Nov 3, 2017 · 3 min read

1. APLS Overview

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Equation 1. APLS metric. Node a’ is the node in the proposal graph G’ nearest the location of node a in the ground truth graph G. L(a,b) denotes a path distance in the ground truth graph G, and L(a’, b’) denotes the path length between the corresponding nodes in the proposal graph.

2. Road Network Comparison Complications

2.1. Node Snapping

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Figure 1. Node snapping procedure. A: Ground truth graph with control nodes. B: Proposal graph. C: Ground truth graph (orange) and ground truth control points (red) overlaid on proposal graph (grey). D: Same as graph C, but showing an 8 meter buffer (yellow) around the proposal graph. E: Ground truth control nodes are injected into the proposal graph at the nearest edge, except for nodes outside the buffer (grey). F: Final proposal graph with nodes injected at the appropriate location to compare to graph A.

2.2. Symmetric Comparisons

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Figure 2. Illustration of the need to apply Equation 1 symmetrically (i.e.: ground truth to proposal, and proposal to ground truth). A: Ground truth graph. B: Proposal graph with many short, spurious connections well outside the buffer. C: Proposal nodes snapped onto the ground truth graph; snapping proposal control points onto the ground truth graph and then computing the metric penalizes the many extraneous predictions (grey nodes).

3. APLS Code

4. Conclusions

The DownLinQ

Welcome to the official blog of CosmiQ Works, an IQT Lab…

Adam Van Etten

Written by

The DownLinQ

Welcome to the official blog of CosmiQ Works, an IQT Lab dedicated to exploring the rapid advances delivered by artificial intelligence and geospatial startups, industry, academia, and the open source community

Adam Van Etten

Written by

The DownLinQ

Welcome to the official blog of CosmiQ Works, an IQT Lab dedicated to exploring the rapid advances delivered by artificial intelligence and geospatial startups, industry, academia, and the open source community

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