PHOTOGRAMMETRIC MEASUREMENT OF SMALL 
COMPONENTS FOR MOTOR VEHICLES 
M A R Cooper 
and 
M R Shortis 
Department of Civil Engineering 
The City University,London 
l. Introduction 
The automobile industry is at present 
interested in developing new techniques to 
carry out standard measuring procedures. 
Because of advances in instrumentation and 
computer systems, one such technique now 
available is close-range photogrammetry. 
A small component typical of those measured 
at the prototype stage and during quality 
control of normal production by an automobile 
manufacturer was subjected to inspection, 
photography and measurement by the Terrestrial 
Photogrammetry Unit of The Department of 
Civil Engineering at The City University, 
London. 
The component had been measured by the 
automobile manufacturer using standard 
techniques. Limited marking of definitive 
points was carried out at that stage. It 
was left to the Unit to show the precision of 
the photogrammetric technique and to indicate 
the ways in which the results of the measure- 
ment could be presented to the automobile 
engineer. 
2. Preparation of the Component 
The component was a model of part of an 
engine cowling, constructed of polished 
wood and about 720 mm x 420 mm x 200 mm.It was 
sprayed with water-based paint to reduce 
surface reflections and aid stereoscopic 
fusion. The paint could afterwards be easily 
removed to return the model to its original 
appearance. 
An existing computer program for single 
terrestrial models was modified to reduce 
measurements taken from the proposed 
configuration for the photography. The 
program converts stereocomparator measure- 
ments into space coordinates as well as 
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giving details of the exterior orientations 
of the cameras, residual parallaxes and 
residuals at control points. 
3. Stereomodel Control 
The control supplied by the manufacturer 
consisted of lines scribed into the model 
surface and an indication of the coordinate 
origin position. This control was considered 
unsatisfactory for photogrammetry primarily 
because of the width and the indistinctness 
of the scribing. Furthermore, there was a 
lack of documentation and some points 
referenced to the coordinate origin would 
not be visible as they were not on the side 
of the component to be photographed. It was 
therefore decided to provide separate control 
suitable for the photogrammetry. 
A grid sheet with an arbitrary origin was 
prepared as a method of controlling the 
Stereomodel. The grid was drawn on polyester 
draughting foil using a coordinatograph 
which has an estimated precision of 0.1 mm 
relative to the origin. The polyester sheet 
was allowed to settle on a flat baseboard 
in constant temperature and humidity. 
The component was then placed on the grid 
and thus had numerous control points (i.e. 
grid intersections) immediately adjacent to 
it. However, because the taking distance was 
à minimum so as to obtain the maximum picture 
scale, there was a large depth range in the 
Stereomodel. Control over this large depth 
range was obtained by standing calibrated 
length bars vertically around the model (see 
Figure l ). These were used in a similar way 
to the use of height control of aerial 
photography. 
4. Photography 
A single &eiss UMK 10/1318 terrestrial camera 
was used for the photography of the component. 
The camera was placed in a specially construct- 
ed mount with the axis approximately vertical. 
The minimum taking distance of 1.6 m was used 
with a small aperture to ensure a large depth 
of field. Black and white emulsion on glass 
plates was used with photoflood lighting and 
a long exposure. A camera base of 400 mm was 
used to give a base/height ratio of 1:4, the 
maximum allowable in relation to possible 
later use of a stereoplotter. 
5, Measurement 
The photographs were first placed in a 
stereocomparator and measurements taken to 
the grid and height-bar control.  Measure- 
ments were also taken to the points marked 
by the manufacturer and the targets 
attached during preparation. 
The photographs were then placed in a 
stereoplotter and orientations carried out 
using the grid and length bar control and 
the exterior orientation parameters produced 
by the computer program. The coordinated 
points on the surface of the component 
were also included as control to check the 
orientations.