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8. Examples of Application
The following examples are chosen in order to show the method applied
to different types of cameras, and also to illustrate the different types of test
objects that are required in the calibration method. All measurements of image
co-ordinates have been performed in the stereocomparator Wild StK 824 at
the Division of Photogrammetry, Stockholm. The accuracy of this instrument
is still the same that given by Hallert in [10].
8.1. PENT AX 24 x 36 MM CAMERA
An ordinary camera with picture size 24 x 36 mm and a Super-Takumar
1:1.8 / 55 mm lens has been calibrated for two focussing distances, infinity and
ten meters. Three calibrations have been made in each case. The camera has
been focussed before every exposure.
8.1.1. 7est Object.
The test object consists of 177 points in a steel framework 3.6 m wide, 2.4 m
high and 2.8 m deep. See Fig. 9. It is placed in the basement of the building,
where the Division of Photogrammetry is located. The walls, floor and ceiling of
the basement move slightly in relation to each other. The framework has then
been designed to minimize geometric deformations of the test object. The frame
work is hinged at point A and point B. The hole in the steel angle at B is oval
shaped to allow expansion and contraction depending on variation in tempera
ture. For the same reason the framework is resting on steel balls (20 mm dia
meter) between steel plates at points C and D. Extending between the upper and
lower frames are steel tubes (5 mm diameter) to which the targets are attached.
The targets have a circular pattern, see Fig. 10, giving symmetric images even
if they are out of focus. The small diagonal cross in the center of the target was
used for the theodolite measurements to determine the co-ordinates of the point.
As the test device could move around point A, and as the tripods of the theo
dolites may move, the measurements were arranged to eliminate these move
ments. The basic idea is that the points are determined by intersection from
three theodolite stations. These stations are defined by resection from reference
points in the test device. Every half-hour the theodolite position was resected
from these reference points and the angles for the intersection were adjusted
