Extraction of low cost houses from a high spatial resolution satellite imagery using Canny edge detection filter

Since its democratic dispensation in 1994, the South African government enacted a number of legislative and policy interventions aimed at availing equal housing opportunities to the previously marginalized citizens. Mismanagement and unreliable reporting has been widely reported in publicly funded housing programmes which necessitated the government to audit and monitor housing development projects in municipalities using more robust and independent methodologies. The objective of this study was therefore to test and demonstrate the effectiveness of high spatial resolution satellite imagery in validating the presence of government funded houses using an object-oriented classification technique that applies a Canny edge detection filter. The results of this study demonstrate that object-orientated classification applied on pan-sharpened SPOT 6 satellite imagery can be used to conduct a reliable inventory and validate the number of houses. The application of the multi-resolution segmentation and Canny edge detection filtering technique proved to be an effective means of mapping individual houses as shown by the high detection accuracy of 99% and quality percentage of 96%.Keywords: Houses, Remote Sensing, SPOT 6, Canny edge detection, Multi-resolution Segmentation, Object-Oriented Classificatio

Extraction of building boundaries using hough transform and perceptual grouping rules from high resolution orthophotos and lidar data

Son yıllarda uzaktan algılama teknolojisindeki gelişmelerle nesne belirleme çalışmalarında artış olmuştur. Özellikle LiDAR (Light Detection and Ranging) verisi ve yüksek konumsal çözünürlüklü görüntülerden bina tespiti en yaygın çalışmalar arasında yer almıştır. Bu çalışmada, yüksek çözünürlüklü renkli (Kırmızı, Yeşil, Mavi) ortofoto ve LiDAR verilerinden otomatik bina çıkarımı için Hough dönüşümü ve algısal gruplama tabanlı bir yaklaşım geliştirilmiştir. Yaklaşımın ön işlemleri, ortofoto ve LiDAR verilerinin referanslandırılması, LiDAR verisinden gürültünün temizlenmesi ve yer filtrelemesi işlemlerini içermektedir. LiDAR verisinden sayısal yüzey modeli (SYM), sayısal arazi modeli (SAM) ve normalize edilmiş SYM (nSYM), ortofotodan da VARI (Visible Atmospherically Resistant Index) bitki indeksi oluşturulur. Sadece bitki ve bina nesnelerini elde etmek için nSYM verisine bir eşik değer uygulanır. Bitki indeksi bandı kullanılarak eşiklenmiş nSYM verisinden bitki alanları maskelenir ve yalnız bina alanlarının kalması sağlanır. Bundan sonra, DoG (Difference of Gaussian) filtresi ile ortofotodan kenarlar çıkarılır. Elde edilen kenar görüntüsünden Hough dönüşümü ile binaları oluşturan çizgi segmentleri çıkarılır ve bu çalışmada uygulanan algısal gruplama kuralları ile çizgi segmentlerinden bina sınırlarının çıkarımı yapılır. Yaklaşım, İzmir ili, Bergama ilçesinden seçilen farklı özelliklere sahip test alanları üzerinde uygulanmıştır. Sonuçların doğruluk analizlerinde piksel-tabanlı ve nesne-tabanlı iki farklı yöntem kullanılmıştır. Piksel tabanlı ve nesne tabanlı yöntemlere göre, ortalama BBBüt (Building Detection Completeness – Bina Belirleme Bütünlüğü) değeri sırasıyla %79.61- %90.76 ve BBDoğ (Bina Belirleme Doğruluğu – Building Detection Correctness) değeri %95.74- %100 olarak hesaplanmıştır. Elde edilen sonuçlar, uygulanan yaklaşımın ortofoto ve LiDAR verilerinden bina çıkarımında oldukça başarılı olduğunu göstermektedir. Elde edilen sonuçlar, uygulanan yaklaşımın ortofoto ve LiDAR verilerinden bina çıkarımında oldukça başarılı olduğunu göstermektedir.In recent years, with the development of remote sensing technology there has been an increase in object detection studies. Especially, building detection from LiDAR data and high resolution images has become one of the most common used studies. In this study, an approach based on Hough transform and perceptual grouping has been developed for automatic building extraction from high resolution orthophotos and LiDAR. Pre-processing of the approach, consists of the registration of LiDAR and orthophotos, noise removal and ground filtering of LiDAR data. Digital Surface- Terrain Model (DSMDTM) and normalized Digital Surface Model (nDSM) are generated from LiDAR, and VARI index is generated from orthophoto. To obtain only the vegetation and the building objects a threshold is applied to nDSM. The vegetation areas are masked from the thresholded nDSM with the vegetation index band and the building areas remained. The edges are extracted from orthophoto using the DoG filter. Line segments that form buildings are extracted from the obtained edge image using Hough transform, and the building boundaries are constructed using these line segments through the developed perceptual grouping rules. The approach was tested on test fields with different characteristics selected from the city of Bergama/ Izmir province, Turkey. Two different methods, pixel and object-based, were used for the accuracy assessments. According to pixel- object-based methods, the average BDCom. rates were %79.61- %90.76 and and BDCor. rates were %95.74- %100, respectively. The results demonstrate that the developed approach is quite successful in the extraction of buildings from orthophotos and LiDAR

Building Extraction from High Resolution Space Images in High Density Residential Areas in the Great Cairo Region

This study evaluates a methodology for using IKONOS stereo imagery to determine the height and position of buildings in dense residential areas. The method was tested on three selected sites in an area of 8.5 km long by 7 km wide and covered by two overlapping (97% overlap) IKONOS images. The images were oriented using rational function models in addition to ground control points. Buildings were identified using an algorithm that utilized the Digital Surface Model (DSM) extracted from the images in addition to the image spectral properties. A digital terrain model was used with the DSM created from the IKONOS stereo imagery to compute building heights. Positional accuracy and building heights were evaluated using corner coordinates extracted from topographic maps and surveyed building heights. The results showed that the average building detection percentage for the test area was 82.6% with an average missing factor of 0.16. When the image rational polynomial coefficients were used to build the image model, results showed a horizontal accuracy of 2.42 and 2.39 m Root Mean Square Error (RMSE) for the easting and northing coordinates, respectively. When ground control points were used, the results improved to the sub-meter level. Differences between building heights extracted from the image model and the corresponding heights obtained through traditional ground surveying had a RMSE of 1.05 m

Estimating Solar Energy Production in Urban Areas for Electric Vehicles

Cities have a high potential for solar energy from PVs installed on buildings\u27 rooftops. There is an increased demand for solar energy in cities to reduce the negative effect of climate change. The thesis investigates solar energy potential in urban areas. It tries to determine how to detect and identify available rooftop areas, how to calculate suitable ones after excluding the effects of the shade, and the estimated energy generated from PVs. Geographic Information Sciences (GIS) and Remote Sensing (RS) are used in solar city planning. The goal of this research is to assess available and suitable rooftops areas using different GIS and RS techniques for installing PVs and estimating solar energy production for a sample of six compounds in New Cairo, and explore how to map urban areas on the city scale. In this research, the study area is the new Cairo city which has a high potential for harvesting solar energy, buildings in each compound have the same height, which does not cast shade on other buildings affecting PV efficiency. When applying GIS and RS techniques in New Cairo city, it is found that environmental factors - such as bare soil - affect the accuracy of the result, which reached 67% on the city scale. Researching more minor scales, such as compounds, required Very High Resolution (VHR) satellite images with a spatial resolution of up to 0.5 meter. The RS techniques applied in this research included supervised classification, and feature extraction, on Pleiades-1b VHR. On the compound scale, the accuracy assessment for the samples ranged between 74.6% and 96.875%. Estimating the PV energy production requires solar data; which was collected using a weather station and a pyrometer at the American University in Cairo, which is typical of the neighboring compounds in the new Cairo region. It took three years to collect the solar incidence data. The Hay- Devis, Klucher, and Reindl (HDKR) model is then employed to extrapolate the solar radiation measured on horizontal surfaces β =0°, to that on tilted surfaces with inclination angles β =10°, 20°, 30° and 45°. The calculated (with help of GIS and Solar radiation models) net rooftop area available for capturing solar radiation was determined for sample New Cairo compounds . The available rooftop areas were subject to the restriction that all the PVs would be coplanar, none of the PVs would protrude outside the rooftop boundaries, and no shading of PVs would occur at any time of the year; moreover typical other rooftop occupied areas, and actual dimensions of typical roof top PVs were taken into consideration. From those calculations, both the realistic total annual Electrical energy produced by the PVs and their daily monthly energy produced are deduced. The former is relevant if the PVs are tied to a grid, whereas the other is more relevant if it is not; optimization is different for both. Results were extended to estimate the total number of cars that may be driven off PV converted solar radiation per home, for different scenarios

The use of Unmanned Aerial Vehicle based photogrammetric point cloud data for winter wheat intra-field variable retrieval and yield estimation in Southwestern Ontario

Precision agriculture uses high spatial and temporal resolution soil and crop information to control the crop intra-field variability to achieve optimal economic benefit and environmental resources sustainable development. As a new imagery collection platform between airborne and ground measurements, Unmanned Aerial Vehicle (UAV) is used to collect high spatial resolution images at a user selected period for precision agriculture. Most studies extract crop parameters from the UAV-based orthomosaic imagery using spectral methods derived from the satellite and airborne based remote sensing. The new dataset, photogrammetric point cloud data (PCD), generated from the Structure from Motion (SfM) methods using the UAV-based images contains the feature’s structural information, which has not been fully utilized to extract crop’s biophysical information. This thesis explores the potential for the applications of the UAV-based photogrammetric PCD in crop biophysical variable retrieval and in final biomass and yield estimation. First, a new moving cuboid filter is applied to the voxel of UAV-based photogrammetric PCD of winter wheat to eliminate noise points, and the crop height is calculated from the highest and lowest points in each voxel. The results show that the winter wheat height can be estimated from the UAV-based photogrammetric PCD directly with high accuracy. Secondly, a new Simulated Observation of Point Cloud (SOPC) method was designed to obtain the 3D spatial distribution of vegetation and bare ground points and calculate the gap fraction and effective leaf area index (LAIe). It reveals that the ground-based crop biophysical methods are possible to be adopted by the PCD to retrieve LAIe without ground measurements. Finally, the SOPC method derived LAIe maps were applied to the Simple Algorithm for Yield estimation (SAFY) to generate the sub-field biomass and yield maps. The pixel-based biomass and yield maps were generated in this study revealed clearly the intra-field yield variation. This framework using the UAV-based SOPC-LAIe maps and SAFY model could be a simple and low-cost alternative for final yield estimation at the sub-field scale. The results of this thesis show that the UAV-based photogrammetric PCD is an alternative source of data in crop monitoring for precision agriculture

Understanding spatial growth and resilience of megacities based on the DPSIR conceptual model:study case: Greater Cairo Metropolis, Egypt

Die Bewältigung stadtplanerischer Aufgaben in komplexen urbanen Systemen, wie des Großraums Kairo (GCM) bedarf eines vertieften Verständnisses dieses sozio-ökologischen Systems. In dieser Studie werden die Konzepte des räumlichen Wachstums und der räumlichen Resilienz genutzt, um über die Analyse der physisch-räumlichen Gegebenheiten hinaus, auf die Prozesse und Beziehungen der Akteure zur sie umgebenden Umwelt zu schließen und zu analysieren, wie sich diese in Raum und Zeit verändert haben. Die Basis bildet das DPSIR-Schema als Rahmenkonzept, um räumliche Indikatoren auf zwei Ebenen abzubilden. Diese resultieren aus pixel- und objektorientierten Klassifikationen von Fernerkundungsdaten (LANDSAT und SPOT), welche die Änderungen in der Landbedeckung und Landnutzung in mehreren Zeitschnitten abbilden. In der Studie konnten über vierzehn Hotspots identifiziert werden, die in verschiedene Kategorien eingeteilt werden konnten. Auf sie sollte die Stadtentwicklung ein verstärktes Augenmerk richten.Planning the sustainable development of complex socio-ecological systems such as the megacity Greater Cairo Metropolis (GCM) requires an understanding of the physical change of the main components of the system. From that point of view, this study introduces the analysis of spatial growth and spatial resilience as two fundamental concepts to find out the relation between social actors and activities, and their physical and environmental expressions and impacts in time and space. The thesis uses the DPSIR conceptual model as a framework to examine spatial indicators on different levels. Both of them represent pixel and object based interpretations of remotedly sensed data (LANDSAT and SPOT) especially focused on land use/land cover change (LULCC). The study could show that there are about fourteen hot spot areas which are in need of different responses e.g. by land management based on their types, properties and spatial features. Most of them can be categorized as open corridors of urban sprawl and saturated closed slums

Merging digital surface models sourced from multi-satellite imagery and their consequent application in automating 3D building modelling

Recently, especially within the last two decades, the demand for DSMs (Digital Surface Models) and 3D city models has increased dramatically. This has arisen due to the emergence of new applications beyond construction or analysis and consequently to a focus on accuracy and the cost. This thesis addresses two linked subjects: first improving the quality of the DSM by merging different source DSMs using a Bayesian approach; and second, extracting building footprints using approaches, including Bayesian approaches, and producing 3D models. Regarding the first topic, a probabilistic model has been generated based on the Bayesian approach in order to merge different source DSMs from different sensors. The Bayesian approach is specified to be ideal in the case when the data is limited and this can consequently be compensated by introducing the a priori. The implemented prior is based on the hypothesis that the building roof outlines are specified to be smooth, for that reason local entropy has been implemented in order to infer the a priori data. In addition to the a priori estimation, the quality of the DSMs is obtained by using field checkpoints from differential GNSS. The validation results have shown that the model was successfully able to improve the quality of the DSMs and improving some characteristics such as the roof surfaces, which consequently led to better representations. In addition to that, the developed model has been compared with the Maximum Likelihood model which showed similar quantitative statistical results and better qualitative results. Perhaps it is worth mentioning that, although the DSMs used in the merging have been produced using satellite images, the model can be applied on any type of DSM. The second topic is building footprint extraction based on using satellite imagery. An efficient flow-line for automatic building footprint extraction and 3D model construction, from both stereo panchromatic and multispectral satellite imagery was developed. This flow-line has been applied in an area of different building types, with both hipped and sloped roofs. The flow line consisted of multi stages. First, data preparation, digital orthoimagery and DSMs are created from WorldView-1. Pleiades imagery is used to create a vegetation mask. The orthoimagery then undergoes binary classification into ‘foreground’ (including buildings, shadows, open-water, roads and trees) and ‘background’ (including grass, bare soil, and clay). From the foreground class, shadows and open water are removed after creating a shadow mask by thresholding the same orthoimagery. Likewise roads have been removed, for the time being, after interactively creating a mask using the orthoimagery. NDVI processing of the Pleiades imagery has been used to create a mask for removing the trees. An ‘edge map’ is produced using Canny edge detection to define the exact building boundary outlines, from enhanced orthoimagery. A normalised digital surface model (nDSM) is produced from the original DSM using smoothing and subtracting techniques. Second, start Building Detection and Extraction. Buildings can be detected, in part, in the nDSM as isolated relatively elevated ‘blobs’. These nDSM ‘blobs’ are uniquely labelled to identify rudimentary buildings. Each ‘blob’ is paired with its corresponding ‘foreground’ area from the orthoimagery. Each ‘foreground’ area is used as an initial building boundary, which is then vectorised and simplified. Some unnecessary details in the ‘edge map’, particularly on the roofs of the buildings can be removed using mathematical morphology. Some building edges are not detected in the ‘edge map’ due to low contrast in some parts of the orthoimagery. The ‘edge map’ is subsequently further improved also using mathematical morphology, leading to the ‘modified edge map’. Finally, A Bayesian approach is used to find the most probable coordinates of the building footprints, based on the ‘modified edge map’. The proposal that is made for the footprint a priori data is based on the creating a PDF which assumes that the probable footprint angle at the corner is 90o and along the edge is 180o, with a less probable value given to the other angles such as 45o and 135o. The 3D model is constructed by extracting the elevation of the buildings from the DSM and combining it with the regularized building boundary. Validation, both quantitatively and qualitatively has shown that the developed process and associated algorithms have successfully been able to extract building footprints and create 3D models