Calculation of Enclosure Index for Assessing Urban Landscapes Using Digital Surface Models

Abstract

Local governments in Japan need to assess landscape quality from the perspective of aesthetics before approving new construction. However, ground surveys are time-consuming and expensive to perform over wide areas. This paper proposes a methodology using a digital surface model (DSM) to estimate a local landscape index, referred to as the “enclosure index”, in urban areas. The index is defined as the ratio of occluded area to the entire field of view. The index can be applied to local landscape assessment from the viewpoint of a human, and it is expected to allow for estimating the landscape quality over a wide area at low cost. The index is defined in two different projections, and two types of DSMs for calculating the index were investigated: DSM from airborne LiDAR (LiDAR-DSM) and DSM generated from stereoscopic aerial images (Image-DSM). Enclosure index (occlusion) maps were generated, and the indices were calculated in the study area of Higashiyama, Kyoto, Japan. As a result of validation based on ground truth data, it was found that the index from LiDAR-DSM was more accurate than that from Image-DSM because the height accuracy of LiDAR-DSM was higher than that of Image-DSM, especially for narrow streets, where three-dimensional coordinates are difficult to restore by using aerial images. Even though last-pulse mode LiDAR data may yield underestimated DSM, it was found that the proposed methodology is effective for estimating the index over a wide area at low cost.