Professor Dr Dipl-Ing., Hans Georg Jerie (1929-2008)
In memoriam (ITC News, ITC, Enschede, The Netherlands, 2008-3, pp25.)
Photogrammetry, the application of photography as an aid to mapping and surveying, was first pioneered during the late nineteenth century. The essential principle was that a number of photographs, taken from different angles, could be used to create a map if they share a common set of identifiable control points. During the mid 20th century, new methods were suggested but required the solution of a large system of simultaneous equations. The analogue computer proposed by Professor HG Jerie of the International Training Centre for Aerial Survey (ITC) in Delft, the Netherlands, was a special purpose, mechanical device for solving these problems. The computer was patented by Information Communication Technology (ICT) and was marketed and manufactured with reasonable success.
In order to use a set of photographs for mapping, it was necessary to calculate the respective positioning of each photograph and to resolve the images by identifying known control points. This is known as aerial triangulation and at the time when Jerie invented his computational aid, a large number of control points were required in order to obtain the generally desired accuracy. By splitting up the area into blocks rather than strips as was then the custom, the problem required fewer control points to be identified; at the same time this led to a large system of simultaneous equations requiring solution. This meant that solution by numerical methods was very difficult and Jerie turned to the application of analogue computing techniques to the problem. His invention, which he referred to as an analogue computer, used a mechanical design in which the unknowns of the equations were represented by elastic connections between photographic plates.
The machine, as shown below, essentially constructed an analogue to the problem. In a typical problem many photographs will overlap, and it is necessary to resolve the different views of each image. In the Jerie computer, the various images were transferred onto overlapping plates and the control points of each plate anchored together. Other than at these anchor points, the plates were free to move within the constraints of their elastic connections, eventually stabilising on a solution that best satisfied the positional constraints between the plates.
