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between the points of the object space and the corresponding points of an image plane. 
This relation is often, and particularly for purposes of theory, represented as a mathe- 
matical central projection. The concepts derived from this idea, however, do not suffice 
for the requirements of instrument construction and instrumentology, which cannot, for 
example, do without considering distortion and the formulation of definitions as mea- 
suring directions. It is therefore necessary to complement the description by mathema- 
tical central projection, by that of the physical process of image formation. Both ways 
of representation are justified. Each of them forms the basis for defining a number of 
concepts, which are termed mathematical and physieal concepts and are proposed for 
standardization. As against this, the writer advises against the standardization of so- 
ealled technical definitions, which consider manufacturing errors in the physical image- 
forming process. The unavoidable coexistence of corresponding mathematical and phy- 
sical concepts entails the risk of burdening the terminology with inconvenient and con- 
fusing duplicate designations for analogous concepts. This risx may be avoided by 
observing certain principles in selecting designations. 
How these speculations work out is shown by the accompanying Table, in which 
mathematical and physical definitions are placed side by side. The most important 
concepts are explained in some detail. 
LITERATURE. 
A comprehensive list of the pertinent literature will be found in the paper by 
R. Roelofs, below. In the present paper, the following publications were principally con- 
sidered: 
1. E. Gotthardt: Zur Frage der Definitionen des Bildhauptpunktes und der Aufnahme- 
achse. 
Allgemeine Vermessungsnachrichten, 1950, pp. 55 to 5T. 
2. R. Roelofs: Distortion, Principal Point, Point of Symmetry, and Calibrated Principal 
Point. 
Photogrammetria, 1950-1951, pp. 49 to 66. 
3. W. Roos: Ueber die Lage der Projektionszentren bei einem Objektiv und ihre Be- 
deutung in der Bildmessung. 
Bildmessung und Luftbildwesen, Vol. 15, 1940, pp. 88 to 96. 
4. W. Roos: Neue Definitionen fuer einige Grundbegriffe der Bildmessung. 
Bildmessung und Luftbildwesen, Vol. 16, 1941, pp. 85 to 96. 
W. Roos: Ueber die Definition des Bildhauptpunktes und der Aufnahmeachse. 
Allgemeine Vermessungsnachrichten (Bildmessung und Luftbildwesen) 1950, pp. 235 
to 243. 
6. F. E. Washer and F. A. Case: Calibration of Precision Airplane Mapping Cameras. 
Journal of Research, National Bureau of Standards, 1950, Photogrammetric Engi 
neering, 1950, pp. 502 to 524. 
7. Photogrammetria, 1950-1951, pp. 101 to 118, especially pp. 113 to 114 and 117 to 118. 
8. Panel discussion. — Cameras, Lenses, and Calibration. Photogrammetric Engi- 
neering, 1951, pp. 391 to 424, especially pp. 401 to 405 and 415 to 415. 
9. Begriffe, Benennungen und Formelgroessen in der Photogrammetric (Bildmessung). 
Entwurf Juni 1951 des Normblattes DIN 3035. 
Mitteilungen der deutschen geodaetischen Kommission (out soon). 
ot