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 
.