Trends in Cad-based Photogrammetric Measurement

In the past few decades, Computer Aided Design (CAD) systems have evolved from 2D tools that assist in construction design to the basis of software systems for a variety of applications, such as (re)design, manufacturing, quality control, and facility management. The basic functions of a modern CAD system are storage and retrieval of 3D data, their construction, manipulation, and visualisation. All these functions are needed in a photogrammetric measurement system. Therefore, photogrammetry benefits from integration with CAD, and thereby from developments in this field. There are two main interpretations of the term CAD-based photogrammetry. The first interpretation is on a system level: there is a trend towards integration of photogrammetric tools in existing CAD systems. The second interpretation is on an algorithmic level: developments in the field of CAD regarding object modelling techniques are being implemented in photogrammetric systems. In practice, the two interpretations overlap to a varying extent. The integrated photogrammetric processing of geometry and topology is defined as a minimum requirement for CAD-based photogrammetry. The paper discusses the relation between CAD and photogrammetry with an emphasis on close-range photogrammetry. Several approaches for the integration of CAD and photogrammetry are briefly reviewed, and trends in CAD-based photogrammetry are outlined. First of all, the trend towards CAD-based photogrammetry is observed. The integration of photogrammetry and CAD increases the efficiency of photogrammetric modelling. One of the reasons for this is the improvement of the user-interface, which allows better interaction with the data. A more fundamental improvement is the use of advanced object modelling techniques such as Constructive Solid Geometry, and the incorporation of geometric object constraints. Furthermore, research emphasis is on CAD-based matching techniques for automatic precise measurement of CAD-models. An overall conclusion remains: the integration of photogrammetry and CAD has great potential for widening the acceptance of photogrammetry, especially in industry. This is firstly because of the improvement in efficiency, and secondly because of the established and well-known concept of CAD.