Solid image

The Solid image is a geomatic (Geomatics) product giving the possibility to measure 3D coordinates from a simple 2D image. The solid image is an easy and complete way to describe 3D objects.

The Concept
A photo image can be considered, from a photogrammetric point of view, a central perspective of the acquired object with good approximation. If the internal and external orientation of the camera are known, in case of a digital image it is possible to establish the direction in the space of each object point represented by a pixel in the image. If only one image is available, it is impossible to determine the spatial X,Y,Z position of such object points, because the simple direction is insufficient: all the points along that direction would give the same image point. By means of a DDEM (Dense Digital elevation model) of the acquired object, every pixel (and therefore every direction in the space) can be associated to the value of distance between the centre of perspective and the object point represented by the pixel itself.

In this way each pixel can be referred to the 3D position of the corresponding object point in an absolute reference system. The DDEM can be derived from an existing map or by the use of surveying instruments and procedures. Recently, a series of new instruments, based on the laser technology (3D scanner), have been introduced on the market, giving the possibility to obtain a DDEM in a quick and cheap way.

The Idea, 2003
Definition, first results and applications of the solid image was presented in the ISPRS (International Society for Photogrammetry and Remote Sensing. The Solid Image has been conceptualized by Prof. Sergio Dequal, and developed by a DITAG Politecnico di Torino research group (Prof. Fulvio Rinaudo, Prof. Andrea Lingua, Dott. Leandro Bornaz).