f
REPORT OF COMMISSION V GV-101
TABLE 1. PARALLAX READINGS AND PARALLAX CORRECTIONS FOR STEREO-PAIR NO. 3
i1. Parallax Parallax Corrected
Point Reading (mm.) Correction (mm.) Parallax (mm.)
a 4.30 —0.04 4.26
b 4.22 +0.04 4.26
C 4.26 +0.00 4.26
d 4.24 +0.02 4.26
e 4.28 —0.02 4.26
f 4.84 —0.04 4.80
g 4.76 +0.04 4.80
h 4.75 +0.02 4.77
i 4.81 —0.02 4.79
i 5.36 —0.02 5.34
k 5.31 +0.02 5.33
1 5.32 +0.01 5.33
m 5.34 —0.01 5.33
n 5.85 0.00 5.85
5) Refer to the MANUAL OF PHOTOGRAMMETRY? for instructions on stere-
ometer-type instruments. The parallax readings and parallax corrections
for stereo-pair No. 3 are given in Table 1.
[f there were no tilt (negative
plane parallel to grid plane), lens dis-
tortion, film distortion, calibration ao 5:99 ere}
error, operator's error in reading the 19 4
parallax, or other inaccuracies, the
parallax correction would be zero for
all points. A parallax correction of
zero for all points is an idealized con-
dition and is never realized in prac-
———
10.00
— 6,00 —————*
tice. However, the parallax correction +8
is so easily computed that it can be 2 1
accomplished mentally. The parallax A
correction permits the simplification
of the procedure outlined in this re- F1G. 6.—Micrometer dimensions of test
port, such as the total disregard for object in millimeters.
lens distortion, location of the princi-
pal point, and the magnitude of tilt. There is a resultant error owing to the
intentional neglect of these and other factors, but the bulk of the resultant error
is compensation in one simple parallax correction operation.
For example, it is known that points a, b, c, d, and e are of equal elevation
since they lie in the plane of the grid. It is also known that parallax readings on
points of equal elevation are identical, under the idealized normal case of
stereophotogrammetry. Selecting point c as the reference (since it is located
near the center of the photograph) point a must be corrected by —0.04 milli-
meter to equal the parallax reading at ¢; b by 40.04 millimeter, d by 4-0.02
millimeter, and e by —0.02 millimeter. All other points are corrected by
mentally interpolating between the correction values for the grid points a,
b. c, d, and e. The correction for point j is —0.02 millimeter since it is approxi-
mately half way between point a with a correction of —0.04 millimeter and
point c, with a correction of 0.00 millimeter.
6) Points a, b, c, d, and e are designated as plane No. 1; points f, g, ^, and
i as plane No. 2; points j, k, I, and m as plane No. 3; and point z as
