on a WILD STK-1 Stereocomparator, which has a least read-out
of 1 micron. The stereocomparator provided the data typed on
paper and simultaneously punched on IBM cards.
A matrix of 81 points (Fig, 17) was marked on the slab
using gummed reinforcements of 1.5 cm and 0.6 cm outer and
inner diameters, respectively (Fig. 18).
The loading and supporting systems in the case of the
bending tests (refer to Fig. 14) are shown in Fig. 16. With
minor modifications in the loading and supporting systems, the
same apparatus was used for the torsion tests (Fig. 15).
3.3. Three-Dimensional Transformation
It might be of some interest to briefly discuss the matters
of control and absolute orientation in the project. The slab
was freely suspended by four (4) steel rods (Fig. 16) and was
free to change its position and attitude as the loads were
applied. Furthermore, the structural group was interested
only in Ax, Ay, and Az deformations rather than absolute x,
y, and z coordinates of discrete targeted points. Taking
these two factors into consideration, there was no point in
securing ''fixed control' beyond the slab being tested.
This situation was taken care of by using a system
of cartesian coordinates which would move or ''float'' together
g
with the slab.
In the absence of ''fixed'' control points, the unitary
orthogonal transformation regularly used in photogrammetry for
absolute orientation could not be used in this case. Instead, a
three-dimensional conformal transformation, based on two inter-