(384) 
The two motions bz and f now having been adjusted, the expression for 
the remaining parallax 4 in the model is known to be: 
A = = ay + xy, + = (b — x)as + (b — x)». 
At N (0,0), à depends only on ya, the motion of the second projector about 
its Z-axis (swing); by removing the parallax at this point with this motion, one 
corrects y». At Nz (b. 0) one corrects y1 in the same way. 
In the plane x = O, À depends only on as, the motion of the second projec- 
tor abouts its y-axis (y-tilt, tip, 0); by removing the parallax at points in this 
plane with this motion, one corrects a». The correction of «i is obtained in the 
same way in the plane x — b. (This should complete the relative orientation). 
This method of operation fails if the model is distorted in the region of the 
points N; and N». But in the plane x —0, x — b, and y — 0 one has respectively, 
À EZ be; biz, 4 bas + by, 4á—x(n—)y)-tby. 
By removing the parallax 1 with the by motion at two points in the plane 
y — o, one obtains two values that permit the determination, graphically for 
example, of by: and bys. If these values are set with the by motion in their re- 
spective plane x — b and x — o, only the parallax due to «1, or a» remains, which 
can be corrected as indicated above. After returning the by to zero, one corrects 
?1 and y» by removing 4 in these same planes by changing the two swing motions. 
If no point satisfies the terrain near the plane x — b, for example, the cor- 
rection of y1 is done at the point of maximum residual parallax in the plane 
y — o after correcting a» and y». The maximum residual parallax in the pair is 
finally removed by adjusting as. 
In the case of a small island, for example, it is possible that the planes x=0 
and x = b cannot be used. After an approximate orientation, the parallax 1 is 
removed with by at two points in the plane y/z = t and at two points of another 
plane y/z=t". The two lines determined by these pairs of points are constructed. 
Their y-coordinates at the origin and at the point x — b have the values, 
respectively 
b (ta2 + ya), b(t'a2 + y2), and b (tei -- e), b (t'as + y1) 
which can be solved for bys and by. 
At a point in the model having an abscissa x and ordinate y, and z such 
that y/z=t, the value of the parallax due only to the error of setting ai, has for 
its expression 
Y— Xyı — (b—x) (tas + ya). 
Consequently, one may introduce with the by-motion 
by = xy1 t (b—x) (tas -F ys) 
where the elements are furnished by the graphic solution. The residual parallax 
is removed by changing the e-setting. y: is corrected then at the same point 
after having returned the by to zero. One can operate in the same way for a» 
and ys. 
Oblique and Panoramic Photographs. The axes of the camera are essenti- 
ally perpendicular to the air base and are strongly inclined from the vertical: 
—Óm