Detecção e extração de vegetação utilizando dados lidar: determinação de indivíduos e aglomerados
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Data
2017-04-28
Autores
Barbosa, Lucas Jamiro
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Universidade Estadual Paulista (Unesp)
Resumo
O Sensoriamento Remoto tem-se mostrado, nos últimos anos, uma excelente ferramenta na aquisição de informações da cobertura da Terra. Dentre os diversos sensores remotos, o sistema de aquisição de dados por varredura LASER (Light Amplification by Stimulated Emission of Radiation) se apresenta como uma ferramenta poderosa na coleta de informações tridimensionais. A tecnologia lidar (Light Detection And Ranging), quando a bordo de aeronaves, pode ser denominada como Airborne Laser Scanning (ALS), diferente dos sistemas aerofotogramétricos de imageamento tradicionais, permite coletar, simultaneamente, pontos com coordenadas 3D sobre copas de árvores, bem como o terreno abaixo dela, em função da capacidade de registro de múltiplos retornos e da divergência do pulso. Por esta razão, esta tecnologia tem sido utilizada em diversas aplicações florestais, como manejo e recuperação florestal, silvicultura, exploração madeireira, dentre outras. Diversas pesquisas têm mostrado a possibilidade de utilização dos dados lidar na extração e delimitação de indivíduos arbóreos e, portanto, na estimativa de variáveis dendrométricas. Desta forma, o desenvolvimento de técnicas que proporcionem a automatização no delineamento das copas das árvores e na estimativa destas informações é de grande interesse. Contudo, grande parte das pesquisas relacionadas à detecção de árvores, delimitação de copa e estimativa de algumas variáveis são desenvolvidas considerando cenários homogêneos e específicos, onde a vegetação é caracterizada pela presença de árvores coníferas e/ou deciduais, ou florestas de exploração madeireira. Portanto, o objetivo desta pesquisa foi a implementação e avaliação de uma técnica que permita detectar indivíduos arbóreos e aglomerados, considerando um cenário urbano heterogêneo e complexo; e, destes indivíduos, estimar variáveis dendrométricas como área da copa; altura da árvore; e raio médio da copa. A metodologia proposta é realizada em três etapas e se baseia no uso do método de crescimento de regiões, aplicado à nuvem de pontos originais, ordenados quanto à altura. Além disso, são usados polígonos convexos visando a extração de indivíduos arbóreos e aglomerados. Para isso, são utilizados três parâmetros: distância mínima, buffer e perímetro comum. Foram realizados experimentos considerando dados reais e cenários diferentes em uma área urbana, para diferentes conjuntos de parâmetros utilizados no processo de delimitação das copas. Os mesmos foram avaliados quanto a acurácia temática, completeza e F-Score, calculados em função de referências obtidas de forma manual. Na delimitação de indivíduos arbóreos e aglomerados, simultaneamente, o maior valor de F-Score foi de 54% e na delimitação de indivíduos e aglomerados, em separado, o melhor resultado obtido foi 74% e 39%, respectivamente. Embora melhorias possam ser feitas visando aumentar estes indicadores, principalmente para aglomerados, pode-se considerar que o método proposto tem potencial de aplicação, sobretudo quando se tem por objetivo a extração de árvores individuais em ambiente urbano.
Remote Sensing has shown to be, in the last years, an excellent way of acquiring Earth’s surface data. Among all remote sensors, the system of data acquisition by LASER (Light Amplification by Stimulated Emission of Radiation) scanning has been presented as a powerful tool for three-dimensional information collection. lidar (Light Detection And Ranging) technology, when onboard of airplanes can be named Airborne Laser Scanning (ALS) and, differently from traditional photogrammetric techniques, allows the collection of simultaneously 3D points over tree crowns, as well as the ground underneath it, due to the recording capacity of multiple echoes arising from the divergence of the pulse. For this reason, this technology has been used in many different forest applications, as management and forest recovery, forestry, logging and others. Some researchers have shown the possibility of using lidar data on tree extraction and crown delineation and, therefore, on the estimation of their dendrometric variables. In this way, the development of techniques that can provide the automation of tree crowns delineation and estimation of this information has increased. However, most of the researches performed ever related to tree detection, canopy delineation and estimation of some dendrometric variables are developed considering homogeneous and specific scenarios where the vegetation is characterized by the presence of coniferous and/or deciduous trees. For this purpose, the objective of this research was the implementation and evaluation of a technique capable of detecting individual trees and clumps, considering a heterogeneous urban scenario. Additionally, from those individual trees some dendrometric variables such as crown area; tree height and average crown radius were estimated. Experiments were conducted considering different study areas in an urban environment varying the parameters used in the crown delineation process. Those experiments were evaluated in terms of thematic accuracy, completeness and F-Score, computed based on reference values obtained manually. When the simultaneous delimitation of arboreal individuals and agglomerates was performed the best F-Score was 54%. For independent processing, the best result was 74% and 39%, respectively, for individuals and agglomerates. Although improvements can be performed aiming to improve those indicators, mainly to clumps, it is possible to consider that the proposed method has potential, especially when the objective is the extraction of individual trees in an urban environment.
Remote Sensing has shown to be, in the last years, an excellent way of acquiring Earth’s surface data. Among all remote sensors, the system of data acquisition by LASER (Light Amplification by Stimulated Emission of Radiation) scanning has been presented as a powerful tool for three-dimensional information collection. lidar (Light Detection And Ranging) technology, when onboard of airplanes can be named Airborne Laser Scanning (ALS) and, differently from traditional photogrammetric techniques, allows the collection of simultaneously 3D points over tree crowns, as well as the ground underneath it, due to the recording capacity of multiple echoes arising from the divergence of the pulse. For this reason, this technology has been used in many different forest applications, as management and forest recovery, forestry, logging and others. Some researchers have shown the possibility of using lidar data on tree extraction and crown delineation and, therefore, on the estimation of their dendrometric variables. In this way, the development of techniques that can provide the automation of tree crowns delineation and estimation of this information has increased. However, most of the researches performed ever related to tree detection, canopy delineation and estimation of some dendrometric variables are developed considering homogeneous and specific scenarios where the vegetation is characterized by the presence of coniferous and/or deciduous trees. For this purpose, the objective of this research was the implementation and evaluation of a technique capable of detecting individual trees and clumps, considering a heterogeneous urban scenario. Additionally, from those individual trees some dendrometric variables such as crown area; tree height and average crown radius were estimated. Experiments were conducted considering different study areas in an urban environment varying the parameters used in the crown delineation process. Those experiments were evaluated in terms of thematic accuracy, completeness and F-Score, computed based on reference values obtained manually. When the simultaneous delimitation of arboreal individuals and agglomerates was performed the best F-Score was 54%. For independent processing, the best result was 74% and 39%, respectively, for individuals and agglomerates. Although improvements can be performed aiming to improve those indicators, mainly to clumps, it is possible to consider that the proposed method has potential, especially when the objective is the extraction of individual trees in an urban environment.
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Palavras-chave
Dados lidar, Varredura LASER, Detecção de árvores, Delimitação de copas, Extração de árvores, Variável dendrométrica, Lidar data, LASER scanning, Tree detection, Canopy delimitation, Tree extraction, Dendrometric variable