Accuracy improvement in area-based matching for structural displacement measurements

Measuring and monitoring of structure deformations such as beams have an essential role in civil structural analysis. Measurements obtained pertaining to their displacements, among others, provide the information needed for the studies on material behaviours and structural designs. These measurements can also provide important indicators regarding to their failures. Under controlled laboratory conditions, these displacements can be determined using, for instance, high precision Linear Voltage Differential Transducers (LVDT). The high precision capabilities of these sensors make them suitable for structural deflection experiments. However, these LVDT sensors face a number of major drawbacks, such as, the sensors may be subjected to movement or damaged during the experiment, and the points measured are at pre-determined locations. In other words, displacements can only be measured at points where the LVDTs sensors are fixed. In addition, when large numbers of points of displacement are required or desired, the use of these sensors becomes prohibitively expensive and laborious. Whilst various researchers have used digital close range photogrammetry and the area-based matching approach in determining movements but work on the use of more than two images and surface models has not been reported. Therefore, this study proposes a revised method of precisely determining the displacements of structures using a multi-image area-based matching approach that uses surface models, i.e. a non-contact method. Experiments on beams under loading were performed under laboratory conditions. A series of multiple digital images were captured simultaneously using three digital single-lens reflex cameras throughout the experiments. The beam’s vertical displacements obtained from the proposed method were then validated by comparing against those obtained from the LVDTs. The results indicate that the mean differences between the displacement obtained from the proposed method and LVDTs are less than 0.5mm.The ttest conducted with a confidence level of 5% revealed that the differences between the two sets of results are not significant. It can be concluded that the use of multi-image area-based image matching using surface models is capable of measuring displacements and be used as an additional approach that complements the traditional methods in beam displacement measurements

Effect of lighting difference in reconstruction of three dimensional dense model using close range photogrammetry

Lighting is one of the main elements in photographic process. Adequate source of lighting is required to give enough illumination to the object. Close Range Photogrammetry (CRP) is one of the technique and it has been used in variety of fields for example forensic, traffic management, archeology, medical, construction and else. These kinds of fields have different condition and environment for instance in term of source of lighting. The lack of illumination on the object can cause many problems, for example the quality of images, the accuracy of the project and more. Therefore, in this study, consumer grade digital camera is used to capture the image of an object and reconstruct the three dimensional (3D) model, under the different of intensity of light. The images were processed by using PhotoModeler Scanner and irfanView software. This software is help to generate the 3D model and histogram graph for analysis and result. For geometry evaluation, the model comparison is conducted between the model from CRP approach and laser scanning method. Lastly, the models constructed give different result depending on the intensity of light used

Effect of lighting difference in reconstruction of three dimensional dense model using close range photogrammetry

Lighting is one of the main elements in photographic process. Adequate source of lighting is required to give enough illumination to the object. Close Range Photogrammetry (CRP) is one of the technique and it has been used in variety of fields for example forensic, traffic management, archeology, medical, construction and else. These kinds of fields have different condition and environment for instance in term of source of lighting. The lack of illumination on the object can cause many problems, for example the quality of images, the accuracy of the project and more. Therefore, in this study, consumer grade digital camera is used to capture the image of an object and reconstruct the three dimensional (3D) model, under the different of intensity of light. The images were processed by using PhotoModeler Scanner and irfanView software. This software is help to generate the 3D model and histogram graph for analysis and result. For geometry evaluation, the model comparison is conducted between the model from CRP approach and laser scanning method. Lastly, the models constructed give different result depending on the intensity of light used

Fotogrametría SfM como herramienta para la preservación del patrimonio cultural de Bogotá (Colombia): Caso de estudio La Rebeca

According to Unesco, cultural heritage is both a product and a process that provides societies with a wealth of resources that are inherited from the past, are created in the present and passed on to future generations for their benefit. According to their needs, each country has regulated and undertaken actions aimed at the conservation of its heritage. In the case of Bogotá (capital of Colombia) different norms have been promulgated seeking to protect and preserve the cultural heritage. In this sense, this project seeks to contribute, from the academy, in the virtualization of the cultural heritage of the city using the available technologies and specifically SfM photogrammetry. For this, about 120 images were acquired from the Rebeca monument, located in the center of the city, and which has had to be reconstructed after several acts of vandalism that have affected its structure. Using a non-metric commercial camera and the free software Regards3D and Meshlab, the 3D reconstruction of this monument was achieved. Although there are aspects to be improved in the capture of the data that guarantee the fulfillment of the objective of this project, the results are promising for the conservation of the cultural heritage of the city to be known by future generationsSegún la Unesco el patrimonio cultural es a la vez un producto y un proceso que suministra a las sociedades un caudal de recursos que se heredan del pasado, se crean en el presente y se transmiten a las generaciones futuras para su beneficio. De acuerdo a sus necesidades, cada país ha reglamentado y emprendido acciones tendientes a la conservación de su patrimonio. En el caso de Bogotá (capital de Colombia) diferentes normas han sido promulgadas buscando proteger y preservar el patrimonio cultural. En ese sentido este proyecto busca aportar, desde la academia, en la virtualización del patrimonio cultural de la ciudad usando las tecnologías disponibles y específicamente la fotogrametría SfM. Para esto, cerca de 120 imágenes fueron adquiridas del monumento de la Rebeca, localizado en el centro de la ciudad, y el cual ha tenido la necesidad de ser reconstruido luego de varios actos de vandalismo que han afectado su estructura. Usando una cámara comercial no métrica y los softwares libres Regards3D y Meshlab se logró la reconstrucción 3D de este monumento. A pesar que hay aspectos por mejorar en la captura de los datos que garanticen el cumplimiento a cabalidad del objetivo de este proyecto, los resultados son prometedores para la conservación del patrimonio cultural de la ciudad para que sean conocidas por futuras generaciones