Three-Dimensional Urban Land Cover Classification by Prior-Level Fusion of LiDAR Point Cloud and Optical Imagery

Yanming Chen,Qiqi Zhao,Xiaoqiang Liu,Yijia Xiao,Sida Wan

doi:10.3390/rs13234928

Abstract

The heterogeneity of urban landscape in the vertical direction should not be neglected in urban ecology research, which requires urban land cover product transformation from two-dimensions to three-dimensions using light detection and ranging system (LiDAR) point clouds. Previous studies have demonstrated that the performance of two-dimensional land cover classification can be improved by fusing optical imagery and LiDAR data using several strategies. However, few studies have focused on the fusion of LiDAR point clouds and optical imagery for three-dimensional land cover classification, especially using a deep learning framework. In this study, we proposed a novel prior-level fusion strategy and compared it with the no-fusion strategy (baseline) and three other commonly used fusion strategies (point-level, feature-level, and decision-level). The proposed prior-level fusion strategy uses two-dimensional land cover derived from optical imagery as the prior knowledge for three-dimensional classification. Then, a LiDAR point cloud is linked to the prior information using the nearest neighbor method and classified by a deep neural network. Our proposed prior-fusion strategy has higher overall accuracy (82.47%) on data from the International Society for Photogrammetry and Remote Sensing, compared with the baseline (74.62%), point-level (79.86%), feature-level (76.22%), and decision-level (81.12%). The improved accuracy reflects two features: (1) fusing optical imagery to LiDAR point clouds improves the performance of three-dimensional urban land cover classification, and (2) the proposed prior-level strategy directly uses semantic information provided by the two-dimensional land cover classification rather than the original spectral information of optical imagery. Furthermore, the proposed prior-level fusion strategy provides a series that fills the gap between two- and three-dimensional land cover classification.

Highlights

Sustainable development of the urban environment is related to human well-being, and monitoring and managing the urban environment have long been a research hotspot wherein two-dimensional land cover products have played an important role [1,2,3]
Optical imagery is classified by a deep convolutional neural network (DCNN), and the result of DCNN is the probability belonging to each class
The light detection and ranging system (LiDAR) point cloud and optical imagery used in this experiment were provided by the International Society for Photogrammetry and Remote Sensing (ISPRS) and downloaded from https://www.isprs.org/education/benchmarks.aspx on 12 July 2019

Summary

Introduction

Sustainable development of the urban environment is related to human well-being, and monitoring and managing the urban environment have long been a research hotspot wherein two-dimensional land cover products have played an important role [1,2,3]. Geoobjects in the urban environment are diverse and have unique three-dimensional structures, such as a building with a roof and façade, or a tree with a height and diameter. While these three-dimensional structures cannot be derived from current two-dimensional land cover products, they should not be neglected in the study of the urban environment, including urban form analysis [4], local climate zone [5], and urban woody biomass estimation [6]. The urban land cover should proceed from two-dimensional to three-dimensional analysis, where the type of land cover is indexed by point cloud instead of pixels in the three-dimensional land cover (Figure 1).

Objectives

Methods

Results

Discussion

Conclusion