Superimposition: Description, precision, applications

Superimposition was developed as an instrumental extension and a further perfection of the photogrammetric stereoplotter. Superimposition implies the injection of a digital line map in the oculairs of a stereoplotter such that photo and data file of a given area can be seen simultaneously, providing a link between stereoplotter and geographic information system. A literature study of four existing superimposition systems (Intergraph, Kern, Wild and Zeiss) was carried out. Tests show that superimposition systems have a precision of 40 microns in the photo and a line thickness of 30 to 70 microns. The value of superimposition lies in the support of the process and in the detection of changes by revision activities. For the evaluation of the precision of data files or measurements, the injection is too inaccurate as compared to the precision of the stereoplotter.