3D data acquisition and object reconstruction
Encyclopedia
3D data acquisition and reconstruction is the generation of three dimensional or spatiotemporal models from sensor data. The techniques and theories, generally speaking, work with most or all sensor types including optical, acoustic, laser scanning, radar, thermal, seismic.
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A semi-automatic method for acquiring 3D topologically structured data from 2D aerial stereo images has been presented by Sisi Zlatanova. The process involves the manual digitizing of a number of points necessary for automatically reconstructing the 3D objects. Each reconstructed object is validated by superimposition of its wire frame graphics in the stereo model. The topologically structured 3D data is stored in a database and are also used for visualization of the objects. Software used for 3D data acquisition using 2D images include e.g. ENSAIS Engineering College TIPHON (Traitement d'Image et PHOtogrammétrie Numérique). CyberCity Modeler, ORPHEUS
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A method for semi-automatic building extraction together with a concept for storing building models alongside terrain and other topographic data in a topographical information system has been developed by Franz Rottensteiner. His approach was based on the integration of building parameter estimations into the photogrammetry process applying a hybrid modeling scheme. Buildings are decomposed into a set of simple primitives that are reconstructed individually and are then combined by Boolean operators. The internal data structure of both the primitives and the compound building models are based on the boundary representation methods
Multiple images are used in Zeng's approach to surface reconstruction from multiple images. A central idea is to explore the integration of both 3D stereo data and 2D calibrated images. This approach is motivated by the fact that only robust and accurate feature points that survived the geometry scrutiny of multiple images are reconstructed in space. The density insufficiency and the inevitable holes in the stereo data should then be filled in by using information from multiple images. The idea is thus to first construct small surface patches from stereo points, then to progressively propagate only reliable patches in their neighborhood from images into the whole surface using a best-first strategy. The problem thus reduces to searching for an optimal local surface patch going through a given set of stereo points from images.
Multi-spectral images are also used for 3D building detection. The first and last pulse data and the normalized difference vegetation index are used in the process.
New measurement techniques are also employed to obtain measurements of and between objects from single images by using the projection, or the shadow as well as their combination. This technology is gaining attention given its fast processing time, and far lower cost than stereo measurements. GeoTango SilverEye technology is the first of this kind commercial product that can produce very realistic city models and buildings from single satellite and aerial images.
Using laser scans and images taken from ground level and a bird's-eye perspective, Fruh and Zakhor present an approach to automatically create textured 3D city models. This approach involves registering and merging the detailed facade models with a complementary airborne model. The airborne modeling process generates a half-meter resolution model with a bird's-eye view of the entire area, containing terrain profile and building tops. Ground-based modeling process results in a detailed model of the building facades.Using the DSM obtained from airborne laser scans, they localize the acquisition vehicle and register the ground-based facades to the airborne model by means of Monte Carlo localization (MCL). Finally, the two models are merged with different resolutions to obtain a 3D model.
Using an airborne laser altimeter, Haala, Brenner and Anders combined height data with the existing ground plans of buildings. The dgound plans of buildings had already been acquired either in analog form by maps and plans or digitally in a 2D GIS. The project was done in order to enable an automatic data capture by the integration of these different types of information. Afterwards virtual reality city models are generated in the project by texture processing, e.g. by mapping of terrestrial images. The project demonstrated the feasibility of rapid acquisition of 3D urban GIS. Ground plans proved are another very important source of information for 3D building reconstruction. Compared to results of automatic procedures, these ground plans proved more reliable since they contain aggregated information which has been made explicit by human interpretation. For this reason, ground plans, can considerably reduce costs in a reconstruction project. An example of existing ground plan data usable in building reconstruction is the digital cadastral map, which provides information on the distribution of property, including the borders of all agricultural areas and the ground plans of existing buildings. Additionally information as street names and the usage of buildings (e.g. garage, residential building, office block, industrial building, church) is provided in the form of text symbols. At the moment the digital cadastral map is build up as a data base covering an area, mainly composed by digitizing pre-existing maps or plans.
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Acquisition
Acquisition can occur from a multitude of methods including 2D images, acquired sensor data and on site sensors.Acquisition from 2D images
3D data acquisition and object reconstruction can be performed using stereo image pairs. Stereo photogrammetry or photogrammetry based on a block of overlapped images is the primary approach for 3D mapping and object reconstruction using 2D images. Close-range photogrammetry has also matured to the level where cameras or digital cameras can be used to capture the close-look images of objects, e.g., buildings, and reconstruct them using the very same theory as the aerial photogrammetry. An example of software which could do this is Vexcel FotoG 5. This software has now been replaced by Vexcel GeoSynth. Another similar software program is Microsoft PhotosynthMicrosoft Photosynth
Photosynth is a software application from Microsoft Live Labs and the University of Washington that analyzes digital photographs and generates a three-dimensional model of the photos and a point cloud of a photographed object. Pattern recognition components compare portions of images to create...
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A semi-automatic method for acquiring 3D topologically structured data from 2D aerial stereo images has been presented by Sisi Zlatanova. The process involves the manual digitizing of a number of points necessary for automatically reconstructing the 3D objects. Each reconstructed object is validated by superimposition of its wire frame graphics in the stereo model. The topologically structured 3D data is stored in a database and are also used for visualization of the objects. Software used for 3D data acquisition using 2D images include e.g. ENSAIS Engineering College TIPHON (Traitement d'Image et PHOtogrammétrie Numérique). CyberCity Modeler, ORPHEUS
Orpheus
Orpheus was a legendary musician, poet, and prophet in ancient Greek religion and myth. The major stories about him are centered on his ability to charm all living things and even stones with his music; his attempt to retrieve his wife from the underworld; and his death at the hands of those who...
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A method for semi-automatic building extraction together with a concept for storing building models alongside terrain and other topographic data in a topographical information system has been developed by Franz Rottensteiner. His approach was based on the integration of building parameter estimations into the photogrammetry process applying a hybrid modeling scheme. Buildings are decomposed into a set of simple primitives that are reconstructed individually and are then combined by Boolean operators. The internal data structure of both the primitives and the compound building models are based on the boundary representation methods
Multiple images are used in Zeng's approach to surface reconstruction from multiple images. A central idea is to explore the integration of both 3D stereo data and 2D calibrated images. This approach is motivated by the fact that only robust and accurate feature points that survived the geometry scrutiny of multiple images are reconstructed in space. The density insufficiency and the inevitable holes in the stereo data should then be filled in by using information from multiple images. The idea is thus to first construct small surface patches from stereo points, then to progressively propagate only reliable patches in their neighborhood from images into the whole surface using a best-first strategy. The problem thus reduces to searching for an optimal local surface patch going through a given set of stereo points from images.
Multi-spectral images are also used for 3D building detection. The first and last pulse data and the normalized difference vegetation index are used in the process.
New measurement techniques are also employed to obtain measurements of and between objects from single images by using the projection, or the shadow as well as their combination. This technology is gaining attention given its fast processing time, and far lower cost than stereo measurements. GeoTango SilverEye technology is the first of this kind commercial product that can produce very realistic city models and buildings from single satellite and aerial images.
Acquisition from acquired sensor data
Semi-Automatic building extraction from LIDAR Data and High-Resolution Images is also a possibility. Again, this approach allows modelling without physically moving towards the location or object. From airborne LIDAR data, digital surface model (DSM) can be generated and then the objects higher than the ground are automatically detected from the DSM. Based on general knowledge about buildings, geometric characteristics such as size, height and shape information are then used to separate the buildings from other objects. The extracted building outlines are then simplified using an orthogonal algorithm to obtain better cartographic quality. Watershed analysis can be conducted to extract the ridgelines of building roofs. The ridgelines as well as slope information are used to classify the buildings per type. The buildings are then reconstructed using three parametric building models (flat, gabled, hipped).Acquisition from on-site sensors
LIDAR and other terrestrial laser scanning technology offers the fastest, automated way to collect height or distance information. LIDAR or laser for height measurement of buildings is becoming very promising. Commercial applications of both airborne LIDAR and ground laser scanning technology have proven to be fast and accurate methods for building height extraction. The building extraction task is needed to determine building locations, ground elevation, orientations, building size, rooftop heights, etc. Most buildings are described to sufficient details in terms of general polyhedra, i.e., their boundaries can be represented by a set of planar surfaces and straight lines. Further processing such as expressing building footprints as polygons is used for data storing in GIS databases.Using laser scans and images taken from ground level and a bird's-eye perspective, Fruh and Zakhor present an approach to automatically create textured 3D city models. This approach involves registering and merging the detailed facade models with a complementary airborne model. The airborne modeling process generates a half-meter resolution model with a bird's-eye view of the entire area, containing terrain profile and building tops. Ground-based modeling process results in a detailed model of the building facades.Using the DSM obtained from airborne laser scans, they localize the acquisition vehicle and register the ground-based facades to the airborne model by means of Monte Carlo localization (MCL). Finally, the two models are merged with different resolutions to obtain a 3D model.
Using an airborne laser altimeter, Haala, Brenner and Anders combined height data with the existing ground plans of buildings. The dgound plans of buildings had already been acquired either in analog form by maps and plans or digitally in a 2D GIS. The project was done in order to enable an automatic data capture by the integration of these different types of information. Afterwards virtual reality city models are generated in the project by texture processing, e.g. by mapping of terrestrial images. The project demonstrated the feasibility of rapid acquisition of 3D urban GIS. Ground plans proved are another very important source of information for 3D building reconstruction. Compared to results of automatic procedures, these ground plans proved more reliable since they contain aggregated information which has been made explicit by human interpretation. For this reason, ground plans, can considerably reduce costs in a reconstruction project. An example of existing ground plan data usable in building reconstruction is the digital cadastral map, which provides information on the distribution of property, including the borders of all agricultural areas and the ground plans of existing buildings. Additionally information as street names and the usage of buildings (e.g. garage, residential building, office block, industrial building, church) is provided in the form of text symbols. At the moment the digital cadastral map is build up as a data base covering an area, mainly composed by digitizing pre-existing maps or plans.
Software
Software used for airborne laser scanning includes OPALS (Orientation and Processing of Airborne Laser Scanning data), ...Cost
The financial costs of 3D data acquisition and object reconstruction are not to be underestimated.- Terrestric laserscandevices (pulse or phase devices) + processing software generally start at a price of 150,000 €. Some less precise devices (as the Trimble VX) cost around 75,000€.
- Terrestric LIDAR systems cost around 300,000 €.
- Systems using regular still cameras mounted on RC helicopters (PhotogrammetryPhotogrammetryPhotogrammetry is the practice of determining the geometric properties of objects from photographic images. Photogrammetry is as old as modern photography and can be dated to the mid-nineteenth century....
) are also possible, and cost around 25,000€. Systems that use still cameras with balloons are even cheaper (around 2,500 €), but require additional manual processing. As the manual processing takes around 1 month of labour for every day of taking pictures, this is thus also still an expensive solution in the long run.
- Obtaining satellite images is also an expensive endeavour. High resolution stereo images (0.5 m resolution) cost around 11,000€. Image satellites include Quikbird, Ikonos. High resolution monoscopic images cost around 5,500€. Somewhat lower resolution images (e.g. from the CORONA satellite; with a 2m resolution) cost around 1.000€ per 2 images. Note that Google Earth images are btw too low in resolution to make an accurate 3D model.
Object reconstruction
After the data has been collected, the acquired (and sometimes already processed) data from images or sensors needs to be reconstructed. This may be done in the same program or in some cases, the 3D data needs to be exported and imported into another program for further refining, and/or to add additional data. Such additional data could be gps-location data, ... Also, after the reconstruction, the data might be directly implemented into a local (GIS) map or a worldwide map such as Google EarthGoogle Earth
Google Earth is a virtual globe, map and geographical information program that was originally called EarthViewer 3D, and was created by Keyhole, Inc, a Central Intelligence Agency funded company acquired by Google in 2004 . It maps the Earth by the superimposition of images obtained from satellite...
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Software
Several software packets are used in which the acquired (and sometimes already processed) data from images or sensors is imported. The software packets include:- Cyclone
- Leica Photogrammetry SuiteLeica Photogrammetry SuiteLeica Photogrammetry Suite is a software application for performing photogrammetric operations on imagery and extracting information from imagery...
- PhotoModelerPhotoModelerPhotoModeler is a software application that performs image-based modeling and close range photogrammetry – producing 3D models and measurements from photography....
- SketchUpSketchUpSketchUp is a 3D modeling program marketed by Google and designed for architectural, civil, and mechanical engineers as well as filmmakers, game developers,...
- Rhinophoto