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illuminated through the grating and also seen 
through it appear bright and form moire 
fringes. 
Referring to Figure 1, which shows the pro- 
jection of light paths to a plane vertical to the 
ruling of the grating, the depth of the fringe 
changes with the position on the object when 
the height of a viewpoint from the grating 
surface is different from that of the light 
source (Figure 1, left). When the height of 
viewpoint is equal to that of light source, the 
depth of each fringe is constant (Figure 1, 
right). The depth of Nth bright fringe is ob- 
tained as follows: 
hs N/(diS, — N) (1) 
where is the height of light source and view 
point from the grid surface, S, is the pitch of 
the grating, and d is the distance between 
light source and the viewpoint, measured 
normal to the ruling of the grating. This 
means that the light source need not neces- 
sarily be a point, but may be a linear light 
source or several light sources aligned with a 
straight line which is parallel to the ruling of 
the grating (multiple light source). The same 
fringe can be obtained also with the light 
source on either side of the viewpoint. 
So, it is possible to erase the shadow on the 
object by using two light sources, one on each 
side of and equidistant from the viewpoint, 
(shadow free illumination). 
Suppose now the grating is translated 
    
   
  
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PHOTOGRAMMETRIC ENGINEERING & REMOTE SENSING, 1975 
parallel in its plane. The bright spots move, 
keeping the same depth from the grating. 
Thus, if the grating is moved during expos- 
ure, the fringes formed by the succession of 
bright spots become continuous lines, and the 
grating structure is averaged out (i.e., elimi- 
nated from) in the picture. As a result, the 
picture becomes clearer and the accuracy of 
the measurement is improved because the 
pitch errors in the grating are averaged over 
the length of translation (technique of mov- 
ing grating). 
APPARATUS 
A schematic diagram of the apparatus is 
shown in Figure 1. The purpose of this ap- 
paratus is to take contour moiré pictures from 
opposing directions in a very short time in 
order to make all-round measurement of a 
living body. Details of the instrument are as 
follows: Camera position | = 1880 mm, 
source offset d = 613 mm; grating, effective 
size 1800 x 800 mm, pitch 1.50 mm, width 
and clearance of threads 1 to 1, blackening 3M 
101 C velvet coating, separation 600 mm, ver- 
tical movement; light source, four 500 watt 
iodyne lamps with cylindrical reflectors for 
each channel; cameras, Nikon F with motor 
drive; C.P. Nikkor f = 35 mm lens. The time 
schedule of operation of the two channels is 
shown in Figure 3. 
The lens should be stopped down to f/11 to 
get good fringe visibility at the maximum 
depth of the field, 600 mm, but in most cases 
  
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Schematic diagram of the principle of moiré topography.