Abstract
The most important aspect of digital terrain model generation from airborne laser scan- ning (ALS) data is that of filtering a point cloud to obtain ground points. Numerous automatic filters have been proposed since ALS data became available. However, to filter out nonground points, a slope threshold is usually introduced to classify points into ground and nonground points; this leads to frequent over-filteringproblems in cliff-like terrains.A solution to this problem is proposed, using a dual-directional slope-based filter originating from a conventional slope-based filter is proposed. This filter is designed as a directional filter in one dimension and is applied to every profile of light detection and ranging (LiDAR) points. In this process, a directional filter is first applied to the profile, and another directional filter is then applied at an angle of 180 deg from the first one. Each directional slope-based filter is complementary to the others, thus avoiding over-filtering. We utilize ISPRS LiDAR data for the test. A comparison of this filter approach with existing meth- ods is presented. The comparison result shows that the proposed method obtains a classification accuracy that is as good as most of the compared methods, but is superior to them with regard to handling data from abrupt surfaces. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI. (DOI: 10.1117/1.JRS.8.083619)
Highlights
The mapping of topographical surfaces has become extremely efficient and accurate since the availability of airborne laser scanning (ALS) systems
The directional slope-based (DS) filter was compared with some known filters, including the filter indicated in the commercial software TerraSolid
When points locate near the landscape boundary, regions outside the test areas where no data were sensed will not provide the geometric information for the DS filtering algorithm to judge the points
Summary
The mapping of topographical surfaces has become extremely efficient and accurate since the availability of airborne laser scanning (ALS) systems. Given that DTMs accurately map the Earth’s surface, a key step in DTM generation is to remove nonground points from ALS point cloud data This process is frequently called pointcloud filtering. Meng et al.[5] utilized a four-directional filter with slope and elevation difference conditions to filter out nonground points They did not estimate an approximate ground surface, which is critical for a slope-based filter. Each directional slope-based filter is complementary to the others, avoiding over-filtering This new algorithm retains sharp topographic features that are over-smoothed by a conventional slope-based filter and upgrades the quality of the generated DTMs. An initial filtering result was first introduced in our previously presented article.[22] In this article, we propose an improvement of a preprocessing step that co-operates with the DS filter for point-cloud filtering. The theoretical formulas of the DS filter and the DTM generation are elucidated
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