Abstract
The introduced research is about 3D modeling technique that can be considered as an assembly point of photography, topography, photogrammetry, and computer graphics. The chapter present survey methods based on spherical panoramas produced by image stitching techniques, which are proved efficient in order to obtain a high metric quality. It is an interactive survey system to generating 3D models of architectural structures and urban scenes. Photogrammetric fundamentals are applied using two different approaches to obtain the 3D model: the first one is by using texture-mapping techniques in the way of creating the virtual models; while the second is by using parametric visual programing process.
TopBackground
The most widespread use of the close-range photogrammetric techniques was for the representation of the facades or elevation of the historic buildings and structures. The most common product was the line drawing, which delineates architectural form. Such surveys are needed by the various disciplines involved in building repair and conservation. However, this field has changed a lot since the early years of development. Similarly with other close range applications and indeed the whole of photogrammetric methodology, the introduction of computers have progressively changed the ways in which the technique works and is applied (Dallas, 1996). In addition, photogrammetry can be used with other technologies in some cases since the barriers between the different surveying disciplines are being broken and integration of the technologies is taking place.
Image-based modeling (IBM) is a photogrammetric application field that intends to obtain, not only the metric data, but also the 3D model directly collimating points on photos. This method is used for geometric surfaces of architectural objects or city modeling. In most cases, the most impressive and accurate results remaining are those that are achieved with interactive approaches. Recently, image-based models can be used also for virtual reality, digital cinematography and urban planning applications.
The research is based on spherical panoramic photos, which are exclusive outcome of the digital image. R. Szeliski has developed the digital multi-image panoramic photo in 1994 for Apple Computers, then, many stitching software came out to combine panoramas by registration, calibration and blending images (Szeliski, 2005)
The interest in panoramic images is growing rapidly. Currently they are used widely and mainly as documentation in several applications such as 3D virtual tours and Street Views. Furthermore, by providing the panorama with accurate information of its location and orientation, it will add a great metric value allowing the users to acquire metric information of the scene. Moreover, they have metric capabilities enabling the 3D evaluation of an architectural object provided at least two panoramas (Fangi, 2007, 2008). The procedure already very well tested, is highly efficient and fast, and has been applied for the metric documentation of many cultural heritage structures (Fangi, Piermattei & Wahbeh, 2013).
Key Terms in this Chapter
Visual Programing: Programming language that lets users create 3D models by manipulating program elements (components) graphically rather than by specifying them textually. Components are usually parametric, therefore, changing any parameter in any step of the process changes the result model. Usually they are available as plugins in 3D modeling software. The most famous application is Grasshopper 3D for Rhinoceros3D, as well, Dynamo Studio and Dynamo for Revit and Vasari.
Orientation: The orientation is the rotation and translation of the panorama to give it the right position and rotation according to a specific coordinate system it is determined by six parameters. If the coordinate system is another Panorama’s system the orientation is called “Relative orientation”. However, if the coordinate system is the global one, it is called the “Absolute orientation”.
Equirectangular Projection: Equirectangular image projections maps the latitude and longitude coordinates of a spherical globe directly onto horizontal and vertical coordinates of a grid, where, in a case of entire sphere, this grid results twice as wide as it is tall. Consequently, horizontal stretching increases further from the poles, with the north and south poles being stretched across the entire upper and lower edges of the flattened grid. Equirectangular projections can show the entire vertical and horizontal angle of view up to 360° x 180°.
Image-based Modeling: It is three-dimensional modeling based on measures derived from images. It unifies tow fields, photogrammetry and computer graphics.
Spherical Photogrammetry: The spherical photogrammetry is here intended the photogrammetric technique making use of the so-called spherical panorama. It is a close-range photogrammetric technique.
Mapping: Or texture mapping, Is the relationship between the texture (raster image) and the 3D model several ways are available to deform the raster image to map it on the 3D model. Standard mapping methods are Planar, Box (cubic), cylindrical and Spherical projections. In this research, spherical projection is used to map an equirectangular image on 3D models. It works as a central projection.
Triangulation: It is the principle used by both photogrammetry and theodolites to produce three dimensional point measurements. By mathematically intersecting converging lines in space.