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In this post we want to talk about Photomodeling, that is the creation of 3D models from 2D pictures taken with an ordinary camera. This method is a cost-effective alternative to laser scanning , for fast documentation and survey, and the final model can be easily exported and shared. It doesn’t mean that it needs less attention: the choice of shooting device , the illumination, the viewpoints from which catch the photos, the number of shots and their quality required a certain degree of accuracy instead.
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First of all, it is necessary to choose the right device to capture the images: nowadays the market offers several typologies of cameras, from the digital compact ones, to the so-called “bridge” and single-lens reflex cameras. For the creation of our 3D models we have chosen the latter kind of camera, because it permits a high control on exposure time, focus, output file and other facilities for image quality control.
The photo-capture must take into consideration every detail of the object, thus, the more the complex and detailed the object, the more the images should be taken. Remember to keep an overlapping of at least 1/3 of the scene between each photo, in order to facilitate the reconstruction process.
Once the shooting is finished, the choice of the software may take two main directions:
- The use of a freeware (i.e. 123D Catch and Recap Photo, both developed by Autodesk)
- The use of a license software (Agisoft Photoscan)
The first ones offer a totally automatic process, in which the calibration of internal parameters and the camera orientation, the principal moments of 3D reconstruction of the scene, are all managed by the server, which then propose the final resulton the online application.
These models can then be edited or reprocessed for a better quality of the polygon mesh (the collection of vertices, edges and faces that define the object shape), although they don’t offer models with a good quality texture (the object skin, carrying the colour information). Moreover, note that model processing may take from few minutes to some hours.
The choice a license software such as Photoscan brings the work to a high control of a number of parameters, either in the alignment phase (calibration and orientation of the cameras), and on the geometry building-up phase, and finally on the realization of the texture. Moreover, the software allows some other editing procedures, scaling of the model, and most of all the exportation of an orthophoto for further measurements in CAD environment.
The great limit of Photoscan is that the models exported in .obj format are actually splitted into two files: the .obj carries the information of the mesh, while another file (usually an image) carries the texture information. This is translated into the difficulty to upload the model in a 3D viewer online without losing the original high quality.
The software listed here permit all to export the 3D models in the most common file formats used in the field of 3D graphic (i.e. .stl, .obj, .ply, .3ds, .dxf).