ELEVATION ON CASING
Figure 2
These values were 0.1 mm and 0.5 mm respeC-
tively at full scale, relative to the
University's control. The larger height error
was subsequently found to be at least partly
attributable to the deformation of the base
board when the component was placed on it for
photography. The rms residual parallax was
0.09 mm at full scale, with a maximum of
0.24 mm.
It can be argued that improved and more
consistent results could be obtained with a
purpose-built grid/height control unit. The
flatness of the grid base is critical, as well
as its ability to withstand the rigours of
travel and heavy components without distortion.
Such a unit could be designed with portability
and quick assembly in mind, as well as
provision for camera mountings.
The final absolute accuracy of the results
is dependent upon the definition of the
manufacturer's datum. Certainly in this case
the definition was unreliable as the marked
points that were measured showed a standard
error of 0.7 mm from their control positions,
which is about 30% larger than the standard
error of the photogrammetry itself.
Better results could be obtained from scribing
on metal components or possibly by defining
the datum and axis orientations relative to
distinct features on the component.
7.2 Future Developments
In a production line with a purpose-built
camera/control frame and adequate photo-
grammetric and computing facilities, a
73
digital representation of a component could
be produced in a few hours. The
representation could consist of coordinates
of premarked points or numerical profiles
and sections. A purely graphical representa-
tion would require more time but components
could be processed at least on a daily basis.
A close liaison between the photogrammetrist
and the motor vehicle engineer is essential.
The photogrammetrist must understand the
significance of the measurements required by
the engineer before the full potential of
photogrammetric techniques is to be realized
in this field.
