Figure 1 below is not a photograph. It is a 3-D model created with Geometra using photographs and subsequently rendered by Geometra from a viewpoint from which no photograph was ever taken.
Figure 1: This is not a photograph
Geometra creates 3-D models from ordinary pictures stored as files on computer disk. These pictures may be obtained by familiar processes such a conventional photography, using a scanner to read the images into the computer or digital photography where photographs are loaded onto the computer straight from the camera.
Obtaining a picture of a real world 3-D object is a familiar process. Be it by manual means such as drawing and painting or automatically using photographic or film means.
Deriving information about a real world 3-D object from a single picture is only possible to a very limited extent. Obviously size is lost as a close up picture of a toy car looks a lot like an picture of a real car taken at a larger distance. Also a single picture can only show a single aspect of an object so a photographs of the front of a house will not contain any information about the back of the house. Proper positional information is also lost. Two objects which line up in the view (of the camera) will appear in the same position on the picture.
With multiple pictures most of these limitations are gone. All points on the object that are now visible in two or more pictures can have their position triangulated. The only thing which remains ambiguous is the scale of the object but if this is important it can be restored if even a single measurement on the object is known.
Geometra aids in the construction of 3-D models from pictures. The basic model creation process works as follows.
A Geometra 3-D model consists of the 3-D positions of a number of points and information on the structures (lines, surfaces) which link up these points to form an object or objects. Geometra can extract photo-textures from the images used to build the model and apply these to the model in perspectively correct fashion.
Once the model has been calculated it can then be used. If measurements are required they can be made directly within the Geometra user interface.
The model can be rendered using Geometra's internal 3-D viewer or the model can be exported in VRML (Virtual Reality Modelling Language) format which is well suited for publication on the internet or in DXF format which is more directly suitable for import into CAD programs. Also it possible to export numerical data on feature co-ordinates for use in spreadsheets or other numerical analysis programs.