Mobile terrestrial LiDAR data-sets in a Spatial Database Framework

Mobile Mapping Systems (MMS) have become important and regularly used platforms for the collection of physical-environment data in commercial and governmental spheres. For example, a typical MMS may collect location, imagery, video, LiDAR and air quality data from which models of the built-environment can be generated. Numerous approaches to using these data to generate models can be envisaged which can help develop detailed knowledge in the monitoring, maintanence and development of our built-environment. In this context, the efficient storing of this raw spatial data is a significant problem such that bespoke and dynamic access is possible for the generation of modeling requirements. This fundamental requirement of managing these data, where upwards of 40 gigabytes per hour of spatial-information can be collected from an MMS survey, poses significant challanges in data management alone. Existing methodologies mantain bespoke, survey oriented approaches to data management and model generation where the original MMS spatial data is not generally used or available outside these requirements. Thus, there is a need for an MMS data management framework where effective storage and access solutions can hold this information for use and analysis in any modeling context. Towards this end we detail our storage solution and the experiments where the procedures for high volume navigation and LiDAR MMS-data loading are analysed and optimised for minimum upload times and maximum access efficiency. This solution is built upon a PostgreSQL Relational Database Management System (RDBMS) with the PostGIS spatial extension and pg bulkload data loading utility

Forest Understory Trees Can Be Segmented Accurately Within Sufficiently Dense Airborne Laser Scanning Point Clouds

Airborne laser scanning (LiDAR) point clouds over large forested areas can be processed to segment individual trees and subsequently extract tree-level information. Existing segmentation procedures typically detect more than 90% of overstory trees, yet they barely detect 60% of understory trees because of the occlusion effect of higher canopy layers. Although understory trees provide limited financial value, they are an essential component of ecosystem functioning by offering habitat for numerous wildlife species and influencing stand development. Here we model the occlusion effect in terms of point density. We estimate the fractions of points representing different canopy layers (one overstory and multiple understory) and also pinpoint the required density for reasonable tree segmentation (where accuracy plateaus). We show that at a density of ~170 pt/m² understory trees can likely be segmented as accurately as overstory trees. Given the advancements of LiDAR sensor technology, point clouds will affordably reach this required density. Using modern computational approaches for big data, the denser point clouds can efficiently be processed to ultimately allow accurate remote quantification of forest resources. The methodology can also be adopted for other similar remote sensing or advanced imaging applications such as geological subsurface modelling or biomedical tissue analysis

Forest Understory Trees Can Be Segmented Accurately Within Sufficiently Dense Airborne Laser Scanning Point Clouds

Airborne laser scanning (LiDAR) point clouds over large forested areas can be processed to segment individual trees and subsequently extract tree-level information. Existing segmentation procedures typically detect more than 90% of overstory trees, yet they barely detect 60% of understory trees because of the occlusion effect of higher canopy layers. Although understory trees provide limited financial value, they are an essential component of ecosystem functioning by offering habitat for numerous wildlife species and influencing stand development. Here we model the occlusion effect in terms of point density. We estimate the fractions of points representing different canopy layers (one overstory and multiple understory) and also pinpoint the required density for reasonable tree segmentation (where accuracy plateaus). We show that at a density of ~170 pt/m² understory trees can likely be segmented as accurately as overstory trees. Given the advancements of LiDAR sensor technology, point clouds will affordably reach this required density. Using modern computational approaches for big data, the denser point clouds can efficiently be processed to ultimately allow accurate remote quantification of forest resources. The methodology can also be adopted for other similar remote sensing or advanced imaging applications such as geological subsurface modelling or biomedical tissue analysis

LiDAR data management pipeline; from spatial database population to web-application visualization

While the existence of very large and scalable Database Management Systems (DBMSs) is well recognized, it is the usage and extension of these technologies to managing spatial data that has seen increasing amounts of research work in recent years. A focused area of this research work involves the handling of very high resolution Light Detection and Ranging (LiDAR) data. While LiDAR has many real world applications, it is usually the purview of organizations interested in capturing and monitoring our environment where it has become pervasive. In many of these cases, it has now become the de facto minimum standard expected when a need to acquire very detailed 3D spatial data is required. However, significant challenges exist when working with these data sources, from data storage to feature extraction through to data segmentation all presenting challenges relating to the very large volumes of data that exist. In this paper, we present the complete LiDAR data pipeline as managed in our spatial database framework. This involves three distinct sections, populating the database, building a spatial hierarchy that describes the available data sources, and spatially segmenting data based on user requirements which generates a visualization of these data in a WebGL enabled web-application viewer. All work presented is in an experimental results context where we show how this approach is runtime efficient given the very large volumes of LiDAR data that are being managed

Densidade de nuvens pontos UAV-Lidar na estimativa da altura de eucalipto em diferentes sistemas de manejo

Orientador: Prof. Dr. Carlos Roberto SanquettaCoorientadora: Profa. Dra. Ana Paula Dalla CorteDissertação (mestrado) - Universidade Federal do Paraná, Setor de Ciências Agrárias, Programa de Pós-Graduação em Engenharia Florestal. Defesa : Curitiba, 23/02/2021Inclui referências: p. 44-55Área de concentração: Manejo FlorestalResumo: O manejo florestal evoluiu para a fronteira 4.0, a qual utiliza tecnologias a seu favor, destas, destacam-se os Lasers scanners, os quais podem mensurar a floresta. Contudo, essa ferramenta é onerosa, de modo que uma alternativa mais barata e de alta densidade de pontos é a união destes sensores com veículos aéreos não tripulados (UAV-Lidar). Logo, deve-se verificar a influência da densidade de pontos na acurácia das métricas da floresta. Neste sentido, objetivou-se avaliar o desempenho de diferentes densidades de nuvens de pontos UAV-Lidar na estimativa da altura individual de Eucalyptus benthamii em sistemas agrosilvipastoris, implantados em 2012. O estudo foi conduzido na fazenda Canguiri, Pinhais, Paraná, na qual foi realizado o censo das árvores, medindo-se o diâmetro e altura. Os dados UAV-Lidar foram coletados com o sistema GatorEye. A nuvem de pontos foi pré-processada no LASTOOLS, onde foi unida e recortada para a área de estudo. Posteriormente, em linguagem de programação R, esta foi homogeneizada em nove diferentes densidades: 2.000, 1.500, 1.000, 500, 250, 100, 50, 25 e 5 pts/m². Estas nove nuvens de pontos foram classificadas quanto ao solo e normalizadas, favorecendo a determinação dos modelos digitais de terreno, superfície e copas. Foi extraído a altura máxima das árvores, com base no pixel mais alto presente no modelo digital de copas e na nuvem de pontos normalizada. As alturas derivadas foram avaliadas em relação as alturas medidas em campo pelo coeficiente de correlação de Pearson, raiz quadrada do erro médio, viés, análise gráfica e teste t pareado. A densidade de 2.000 pts/m² melhor representou o perfil da árvore e o solo, obtendo maior correlação (0,79) e menor RMSE (14,55 %). Em todas as densidades, as alturas derivadas e mensuradas foram estatisticamente semelhantes. A redução da densidade de pontos ocasionou divergências no perfil da árvore e modelo de copas, não havendo grandes diferenças no modelo digital do terreno. O sistema GatorEye foi acurado para derivar a altura total do Eucalyptus benthamii. Até 100 pts/m² não há perda de acurácia na derivação da altura.Abstract: The 4.0 frontier has arrived in the forest management, employing technologies in its benefit, among them, Lasers scanners, which measure the forest. However, this tool is expensive, so a cheaper and high point density alternative is the union of these sensors with unmanned aerial vehicles (UAV-Lidar). Therefore, the point density influence on the forest metrics' accuracy should be verified. We evaluate the performance of UAV-Lidar's different point cloud densities in the individual height of the Eucalyptus benthamii estimates on different Crop-Livestock-Forest systems, implemented in 2012. It was conducted at Canguiri Farm, Pinhais, Paraná, where the census of the trees was performed, measuring the diameter and height. The UAV-Lidar data were collected with the GatorEye system. The Point Cloud was pre-processing in the LASTOOLS software, where it was merged and clipped into the study area. Then in R programming language, it was thinned in nine densities: 2,000, 1,500, 1,000, 500, 250, 100, 50, 25 and 5 pts/m². The point clouds were classified in ground and normalized, improving the digital models of terrain, surface, and crown. The highest tree height was extracted, based on the highest pixel on the digital crown model and the normalized point cloud. Heights were evaluated by Pearson's correlation, rootsquare- mean error, bias, graphic analysis, and paired t-test. The processing was performed in R language. The tree's profile and the soil were better represented by 2,000 returns.m-², obtaining higher correlation (0.79) and lower RMSE (14.55 %). At all densities, the derived and measured heights were statistically similar. The point cloud density's reduction produced variances in tree profile and CHM, with few differences in DTM. The GatorEye system was accurate to derive the Eucalyptus benthamii's total height. There is no accuracy decrease in the height's derivation until 100 returns.m-²

AUTOMATED TREE-LEVEL FOREST QUANTIFICATION USING AIRBORNE LIDAR

Traditional forest management relies on a small field sample and interpretation of aerial photography that not only are costly to execute but also yield inaccurate estimates of the entire forest in question. Airborne light detection and ranging (LiDAR) is a remote sensing technology that records point clouds representing the 3D structure of a forest canopy and the terrain underneath. We present a method for segmenting individual trees from the LiDAR point clouds without making prior assumptions about tree crown shapes and sizes. We then present a method that vertically stratifies the point cloud to an overstory and multiple understory tree canopy layers. Using the stratification method, we modeled the occlusion of higher canopy layers with respect to point density. We also present a distributed computing approach that enables processing the massive data of an arbitrarily large forest. Lastly, we investigated using deep learning for coniferous/deciduous classification of point cloud segments representing individual tree crowns. We applied the developed methods to the University of Kentucky Robinson Forest, a natural, majorly deciduous, closed-canopy forest. 90% of overstory and 47% of understory trees were detected with false positive rates of 14% and 2% respectively. Vertical stratification improved the detection rate of understory trees to 67% at the cost of increasing their false positive rate to 12%. According to our occlusion model, a point density of about 170 pt/m² is needed to segment understory trees located in the third layer as accurately as overstory trees. Using our distributed processing method, we segmented about two million trees within a 7400-ha forest in 2.5 hours using 192 processing cores, showing a speedup of ~170. Our deep learning experiments showed high classification accuracies (~82% coniferous and ~90% deciduous) without the need to manually assemble the features. In conclusion, the methods developed are steps forward to remote, accurate quantification of large natural forests at the individual tree level