rry the local
ation effect).
> around the
rofile effect).
(gyro drift).
larly to these
ous reference
be forced to
' short-period
e which only
raft, increase
coriolis accel-
>” per minute
nd partly ac-
y. The errors
servo system
ertical. If, by
pensated for,
still be of the
ormance of a
ig the last 20
he laboratory
indard errors
he A-27 gyro
raud type 67
ight and level
orm 1” on the
wer, corrected
rs= 5.4.10.
nstruments to
are equivalent
o to all other
vity reference
s of this prin-
eck of vertical
gyro and its
ut solely as a
can be useful
nadir indica-
'stems become
ts.
quer couplings
icult to obtain
1. This can be
onstruction of
nera’s and the
'ormance.
SURVEY NAVIGATION, CORTEN 81
5. Navigation and orientation methods determining complete spatial position and
attitude.
5.1. Star tracking.
Automatic star tracking is a relatively new development. In space navigation, celes-
tial bodies provide the only rigid reference frame.
Principle.
A telescope, mounted on an inertial platform, is supplied with a photo-electric sen-
sor; this sensor, once it is locked onto a star, feeds a servo system so as to continuously
point the telescope to the star. If the platform is truly horizontal, and if two angles — e.g.
altitude and true azimuth of the celestial body — are measured, the standpoint's position
can be computed. This is done in an anolog computer. The output can be displayed or be
introduced into other systems.
Automatic astro compass.
Applications of these principles are the automatic astro compasses e.g. the MD-1 of
Kollsman Instrument Corp. The MD-1 tracks a celestial body photo-electrically and supplies
o
1 ;
a true heading output continuously with mean error not more than 10 Some of the dif-
ficulties inherent to this principle are the signal-to-noise ratio in daylight and the neces-
sity of a highest-accuracy inertial platform.
Applications.
In aerial survey, such extremely accurate heading information can be useful
a. for survey navigation as such: conservative precision compasses do not supply the
heading closer than 1/,°;
b. for coupling this accurate heading to a Doppler DR computer (the Doppler not being
more accurate than its attitude information);
c. for coupling this angular reference onto an inertial system in order to keep its drift
within close limits.
Applications b. and c. are examples of the useful combination of various systems.
Similar system integrations of extremely high accuracy may become of value to photo-
grammetry in the near future.
5.2. Inertial navigation.
Great efforts are being expended in the development of inertial navigational systems.
These systems provide help in flight line navigation, particularly if provided with a
navigational computer, and they supply verticality information for the control of the
camera's optical axis. It may be expected that inertial navigation can provide basic
improvements to future aerial photography.
Definition.
Inertial navigation systems can be characterized by:
1. an inertial or stable platform which is gyro stabilized with respect to space or with
respect to the earth's horizon;
2. accelerometers mounted on this inertial platform, sensing the vehicle's accelerations
and transducing these accelerations into electrical signals;
8. integration of these accelerations (a) over the time (t) so as to obtain the vehicle’s
ry
speed V, — | a .dt;
0
.