scholarly journals Automatic Extraction of Road Points from Airborne LiDAR Based on Bidirectional Skewness Balancing

2020 ◽  
Vol 12 (12) ◽  
pp. 2025
Author(s):  
Jorge Martínez Sánchez ◽  
Francisco Fernández Rivera ◽  
José Carlos Cabaleiro Domínguez ◽  
David López Vilariño ◽  
Tomás Fernández Pena
Keyword(s):  
Urban Areas ◽  
Local Density ◽  
Airborne Lidar ◽  
Critical Parameters ◽  
Automatic Extraction ◽  
Intensity Threshold ◽  
Key Factor ◽  
Optimal Intensity ◽  
Study Sites ◽  
Manual Input

Road extraction from Light Detection and Ranging (LiDAR) has become a hot topic over recent years. Nevertheless, it is still challenging to perform this task in a fully automatic way. Experiments are often carried out over small datasets with a focus on urban areas and it is unclear how these methods perform in less urbanized sites. Furthermore, some methods require the manual input of critical parameters, such as an intensity threshold. Aiming to address these issues, this paper proposes a method for the automatic extraction of road points suitable for different landscapes. Road points are identified using pipeline filtering based on a set of constraints defined on the intensity, curvature, local density, and area. We focus especially on the intensity constraint, as it is the key factor to distinguish between road and ground points. The optimal intensity threshold is established automatically by an improved version of the skewness balancing algorithm. Evaluation was conducted on ten study sites with different degrees of urbanization. Road points were successfully extracted in all of them with an overall completeness of 93%, a correctness of 83%, and a quality of 78%. These results are competitive with the state-of-the-art.

scholarly journals Performance Comparison of Filtering Algorithms for High-Density Airborne LiDAR Point Clouds over Complex LandScapes

2021 ◽  
Vol 13 (14) ◽  
pp. 2663
Author(s):  
Chuanfa Chen ◽  
Jiaojiao Guo ◽  
Huiming Wu ◽  
Yanyan Li ◽  
Bo Shi
Keyword(s):  
Urban Areas ◽  
Total Error ◽  
Point Clouds ◽  
Performance Comparison ◽  
High Density ◽  
Airborne Lidar ◽  
Type I ◽  
Filtering Algorithms ◽  
Study Sites ◽  
Complex Landscapes

Airborne light detection and ranging (LiDAR) technology has become the mainstream data source in geosciences and environmental sciences. Point cloud filtering is a prerequisite for almost all LiDAR-based applications. However, it is challenging to select a suitable filtering algorithm for handling high-density point clouds over complex landscapes. Therefore, to determine an appropriate filter on a specific environment, this paper comparatively assessed the performance of five representative filtering algorithms on six study sites with different terrain characteristics, where three plots are located in urban areas and three in forest areas. The representative filtering methods include simple morphological filter (SMRF), multiresolution hierarchical filter (MHF), slope-based filter (SBF), progressive TIN densification (PTD) and segmentation-based filter (SegBF). Results demonstrate that SMRF performs the best in urban areas, and compared to MHF, SBF, PTD and SegBF, the total error of SMRF is reduced by 1.38%, 48.21%, 48.25% and 31.03%, respectively. MHF outperforms the others in forest areas, and compared to SMRF, SBF, PTD and SegBF, the total error of MHF is reduced by 1.98%, 35.87%, 45.11% and 9.42%, respectively. Moreover, both SMRF and MHF keep a good balance between type I and II errors, which makes the produced DEMs much similar to the references. Overall, SMRF and MHF are recommended for urban and forest areas, respectively, and MHF averagely performs slightly better than SMRF on all areas with respect to kappa coefficient.

scholarly journals Mobilities of Older Chinese Rural-Urban Migrants: A Case Study in Beijing

2019 ◽  
Vol 16 (3) ◽  
pp. 488 ◽  
Author(s):  
Yang Cheng ◽  
Mark Rosenberg ◽  
Rachel Winterton ◽  
Irene Blackberry ◽  
Siyao Gao
Keyword(s):  
Urban Areas ◽  
Comparative Method ◽  
Service Planning ◽  
Urban Migration ◽  
Rapid Urbanization ◽  
Older Migrants ◽  
Urban Migrants ◽  
Key Factor ◽  
Study Sites ◽  
Cultural Mobility

Along with the rapid urbanization process in Beijing, China, the number of older rural-urban migrants is increasing. This study aims to understand how Chinese rural-urban migration in older age is influenced by, and impacts on the migrants’ mobilities. This study draws on a new conceptual framework of mobile vulnerability, influenced by physical, economic, institutional, social and cultural mobility, to understand older people’ experiences of migration from rural to urban areas. Forty-five structured in-depth interviews with older rural-urban migrants aged 55 and over were undertaken in four study sites in Beijing, using the constant comparative method. Results demonstrate that rural household registration (hukou) is an important factor that restricts rural older migrants’ institutional mobility. As older migrants’ physical mobility declines, their mobile vulnerability increases. Economic mobility is the key factor that influences their intention to stay in Beijing. Older migrants also described coping strategies to improve their socio-cultural mobility post-migration. These findings will inform service planning for older rural-urban migrants aimed at maintaining their health and wellbeing.

scholarly journals Estimating Environmental Contamination and Element Deposition at an Urban Area of Central Italy

Urban Science ◽  
2019 ◽  
Vol 3 (3) ◽  
pp. 76 ◽  
Author(s):  
Stefano Loppi ◽  
Adelmo Corsini ◽  
Luca Paoli
Keyword(s):  
Urban Area ◽  
Environmental Contamination ◽  
Urban Areas ◽  
Central Italy ◽  
Protective Role ◽  
Evernia Prunastri ◽  
Physico Chemical ◽  
Living Organisms ◽  
Study Sites ◽  
Economic Constraints

Air quality monitoring in many urban areas is based on sophisticated and costly equipment to check for the respect of environmental quality standards, but capillary monitoring is often not feasible due to economic constraints. In such cases, the use of living organisms may be very useful to complement the sparse data obtained by physico-chemical measurements. In this study, the bioaccumulation of selected trace elements (Al, As, Cd, Ce, Cr, Cu, Fe, Ni, Pb, S, Sb, Zn) in lichen samples (Evernia prunastri) transplanted for three months at an urban area of Central Italy was investigated to assess the main environmental contaminants, their sources, and the fluxes of element depositions. The results pinpointed Cu and Sb as the main contaminants and suggested a common origin for these two elements from non-exhaust sources of vehicular traffic, such as brake abrasion. Most study sites were, however, found to be subjected to low or moderate environmental contamination, and the lowest contamination corresponded to the main green areas, confirming the important protective role of urban forests against air pollution. Ranges of estimated mean annual element deposition rates in the study area were similar or lower than those reported for other urban areas.

scholarly journals Insects in the City: Does Remnant Native Habitat Influence Insect Order Distributions?

Diversity ◽  
2021 ◽  
Vol 13 (4) ◽  
pp. 148
Author(s):  
Mani Shrestha ◽  
Jair E. Garcia ◽  
Freya Thomas ◽  
Scarlett R. Howard ◽  
Justin H. J. Chua ◽  
...  
Keyword(s):  
Urban Areas ◽  
Rapid Expansion ◽  
Ecological Value ◽  
Native Habitat ◽  
Insect Order ◽  
Insect Pollinator ◽  
Pollinating Insects ◽  
Study Sites ◽  
Taxonomic Groups

There is increasing interest in developing urban design principles that incorporate good ecological management. Research on understanding the distribution and role of beneficial pollinating insects, in particular, is changing our view of the ecological value of cities. With the rapid expansion of the built environment comes a need to understand how insects may be affected in extensive urban areas. We therefore investigated insect pollinator capture rates in a rapidly growing and densely urbanized city (Melbourne, Australia). We identified a remnant native habitat contained within the expansive urban boundary, and established study sites at two nearby populated urban areas. We employed standard pan trap sampling techniques to passively sample insect orders in the different environments. Our results show that, even though the types of taxonomic groups of insects captured are comparable between locations, important pollinators like bees and hoverflies were more frequently captured in the remnant native habitat. By contrast, beetles (Coleoptera) and butterflies/moths (Lepidoptera) were more frequently observed in the urban residential regions. Our results suggest that the maintenance of native habitat zones within cities is likely to be valuable for the conservation of bees and the ecosystem services they provide.

scholarly journals Supervised Classification of Power Lines from Airborne LiDAR Data in Urban Areas

2017 ◽  
Vol 9 (8) ◽  
pp. 771 ◽  
Author(s):  
Yanjun Wang ◽  
Qi Chen ◽  
Lin Liu ◽  
Dunyong Zheng ◽  
Chaokui Li ◽  
...  
Keyword(s):  
Urban Areas ◽  
Supervised Classification ◽  
Airborne Lidar ◽  
Power Lines ◽  
Lidar Data ◽  
Airborne Lidar Data

scholarly journals Application and Validation of a Model for Terrain Slope Estimation Using Space-Borne LiDAR Waveform Data

2018 ◽  
Vol 10 (11) ◽  
pp. 1691 ◽  
Author(s):  
Xuebo Yang ◽  
Cheng Wang ◽  
Sheng Nie ◽  
Xiaohuan Xi ◽  
Zhenyue Hu ◽  
...  
Keyword(s):  
Surface Characteristics ◽  
Airborne Lidar ◽  
Estimation Accuracy ◽  
Estimation Model ◽  
Large Area ◽  
Waveform Data ◽  
Terrain Slope ◽  
Lidar Measurements ◽  
Slope Estimation ◽  
Study Sites

The terrain slope is one of the most important surface characteristics for quantifying the Earth surface processes. Space-borne LiDAR sensors have produced high-accuracy and large-area terrain measurement within the footprint. However, rigorous procedures are required to accurately estimate the terrain slope especially within the large footprint since the estimated slope is likely affected by footprint size, shape, orientation, and terrain aspect. Therefore, based on multiple available datasets, we explored the performance of a proposed terrain slope estimation model over several study sites and various footprint shapes. The terrain slopes were derived from the ICESAT/GLAS waveform data by the proposed method and five other methods in this study. Compared with five other methods, the proposed method considered the influence of footprint shape, orientation, and terrain aspect on the terrain slope estimation. Validation against the airborne LiDAR measurements showed that the proposed method performed better than five other methods (R2 = 0.829, increased by ~0.07, RMSE = 3.596°, reduced by ~0.6°, n = 858). In addition, more statistics indicated that the proposed method significantly improved the terrain slope estimation accuracy in high-relief region (RMSE = 5.180°, reduced by ~1.8°, n = 218) or in the footprint with a great eccentricity (RMSE = 3.421°, reduced by ~1.1°, n = 313). Therefore, from these experiments, we concluded that this terrain slope estimation approach was beneficial for different terrains and various footprint shapes in practice and the improvement of estimated accuracy was distinctly related with the terrain slope and footprint eccentricity.

Urban Thematic Mapping by Integrating LiDAR Point Cloud with Colour Imagery

GEOMATICA ◽  
2011 ◽  
Vol 65 (4) ◽  
pp. 375-385 ◽  
Author(s):  
Haiyan Guan ◽  
Jonathan Li ◽  
Michael A. Chapman
Keyword(s):  
Urban Areas ◽  
Point Cloud ◽  
Local Variation ◽  
Airborne Lidar ◽  
Aerial Imagery ◽  
Building Detection ◽  
Thematic Mapping ◽  
Airborne Lidar Data ◽  
Spectral Channels ◽  
Height Data

This paper presents an effective approach to integrating airborne lidar data and colour imagery acquired simultaneously for urban mapping. Texture and height information extracted from lidar point cloud is integrated with spectral channels of aerial imagery into an image segmentation process. Then, the segmented polygons are integrated with the extracted geometric features (height information between first- and lastreturn, eigenvalue-based local variation and filtered height data) and spectral features (line segments) into a supervised classifier. The results for two different urban areas in Toronto, Canada, demonstrated that a satisfactory overall accuracy of 84.96% and Kappa of 0.76 were achieved in Scene I, while a building detection rate of 92.11%, comission error of 2.10% and omission error of 9.25% were obtained in Scene II.

scholarly journals The Cross Roads of Heritage

2021 ◽  
Author(s):  
◽  
Philippa Dalgety
Keyword(s):  
New Zealand ◽  
Urban Areas ◽  
Large Scale ◽  
Adaptive Reuse ◽  
Built Form ◽  
Depth Analysis ◽  
Key Factor ◽  
History Of ◽  
Fit For Purpose ◽  
The Town

<p>This research explores an approach for adaptive reuse to enhance livability and greater connection to place within provincial towns of New Zealand. There are existing buildings which are often left in disrepair or considered too expensive to refurbish or strengthen. They are often demolished with little consideration to the building’s significance, therefore adaptive reuse has become a missed opportunity in New Zealand.  Many of our provincial cities have uninhabited large-scale buildings, which need upgrading due to being outdated and no longer fit for purpose. Seismic upgrading is a key factor in why these buildings are left uninhabited. One of the urban areas which this is prevalent is Whanganui. Whanganui has the opportunity to blend the old and the new built form to create a revitalized and timeless street appearance.   The regeneration of Whanganui can be achieved through adaptive reuse to enhance the crafted beauty of the town through its architecture. The revitalization of Whanganui can give guidance to other provincial cities in New Zealand while enhancing the quality of life within the town.  An in-depth analysis of the history of Whanganui, will allow for heritage significance to play a major role in the redesign. This design will be developed at three different scales to demonstrate how the built form can enhance connection to place and livability. These scales are at an urban, a built and a detailed scale.   The main cross roads linking the city of Whanganui to its river is surrounded by character and historical buildings. It will be used as a key area illustrating Whanganui’s past to better inform the future.</p>

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