Abstract
Roadway elevation data is critical for a variety of transportation analyses. However, it has been challenging to obtain such data and most roadway GIS databases do not have them. This paper intends to address this need by proposing a method to extract roadway elevation data from Google Earth (GE) for transportation applications. A comprehensive accuracy assessment of the GE-extracted elevation data is conducted for the area of conterminous USA. The GE elevation data was compared with the ground truth data from nationwide GPS benchmarks and roadway monuments from six states in the conterminous USA. This study also compares the GE elevation data with the elevation raster data from the U.S. Geological Survey National Elevation Dataset (USGS NED), which is a widely used data source for extracting roadway elevation. Mean absolute error (MAE) and root mean squared error (RMSE) are used to assess the accuracy and the test results show MAE, RMSE and standard deviation of GE roadway elevation error are 1.32 meters, 2.27 meters and 2.27 meters, respectively. Finally, the proposed extraction method was implemented and validated for the following three scenarios: (1) extracting roadway elevation differentiating by directions, (2) multi-layered roadway recognition in freeway segment and (3) slope segmentation and grade calculation in freeway segment. The methodology validation results indicate that the proposed extraction method can locate the extracting route accurately, recognize multi-layered roadway section, and segment the extracted route by grade automatically. Overall, it is found that the high accuracy elevation data available from GE provide a reliable data source for various transportation applications.
Highlights
This paper aims at evaluating Google Earth as a possible elevation data source for transportation applications
To understand the accuracy of Google Earth (GE) elevation data, a comprehensive accuracy assessment on GE elevation data was conducted in the area of conterminous USA
The GE elevation data was compared with the ground truth data from nationwide GPS benchmarks and six states’ roadway monuments in the conterminous USA
Summary
Roadway elevation data play a critical role in a wide range of transportation analysis and design applications including roadway geometric design, infrastructure construction, safety. The prevailing feature of the errors caused by overlapping infrastructure is that the elevation along the lower layer route suddenly steps upward to the elevation of top layer in the overlapping segment, and falls back to lower layer elevation at the end of overlap Based on this characteristic, the following method has been developed to recognize the overlapping area: first, ΔEi and ti are defined in Eqs 6 and 7, describing the elevation difference and variation trend between each sampling point i and its previous one. The method assumes that the infrastructure overlapping will not occur at the starting or ending section of the extracting route, and compares all the subsequent sampling points iteratively by the following procedure to find the overlapping areas and correct the elevation: 1.
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