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philosophies exist. Fairey Surveys operates - as far as possible - on the basis of available 
ground control. The required minimum ground control depends on the accuracy to be achieved 
and on the type of area. If ample ground control is available it is the trend to perform aerial 
friangulation without auxiliary data. Such data, with exception of statoscope data and APR data 
is considered as good second best to ground control except for small scale surveys and mapping. 
According to Huntings Surveys maximum distances between given ground control of up to 60 to 
80 miles are considered as feasible for APR controlled photo strips. - As far as the accuracy 
is concerned which is obtained with instruments producing auxiliary data, or which is inherent 
to auxiliary data or which is obtained by aerial triangulation with auxiliary data the following 
information is available ; Directorate of Overseas Surveys : For spot heights determined by 
APR an accuracy of 5 to 6 feet can be expected up to a flight height of 25, 000 ft which is the air 
craft ceiling for a Dakota. Fairey Surveys : For a rectangular area of 17, 000 sq. miles in Aden 
control was provided with APR from a flight height of 15, 000 ft and using a RC 6 A spotting ca - 
mera with 70 mm focal length. The 14 North-South and the 7 East-West APR lines beginning at 
sea level closed on each other to the order of about 20 ft. after Henry's formula corrections 
had been applied. Infra-red horizon photography was tested in Bechuanaland Protectorate and 
Tanganyika. These tests encountered difficulties in distinguishing the true horizon on the hori 
zon pictures and no numerical accuracy information is available. Huntings Surveys : An area of 
1500 sq. mi. in Nigeria was covered with 11 longitudinal (48 overlaps per strip) and 3 tie strips 
using APR controlled photography (mapping scale 1 : 50, 000, contour interval 20 ft). The maxi 
mum residual elevation errors were smaller than 10 ft. when checked against control heights 
and 80 % of the residual elevation errors were smaller than 5 ft. (Reference is made to " Char 
tered Surveyor " Nov. 1961, pp. 234-235). In West Africa a 4° x 4° square area of 40, 000 sq.mi. 
for mapping in the scale 1 : 100, 000 with 50 m contours was covered by North-South strips (75 
overlaps per strip) and 5 East-West strips at 1/2° intervals using APR and statoscope control 
led photography as well as available control at the western edge and control extended across 
the area by tellurometer and by Zeiss Ni 2 levels in clusters at 120 mi. intervals. The adjust 
ment of this block was performed by means of the Elliot 803 electronic computer. The maximum 
residual errors were less than 40 m and 86 percent of the residual errors were less than 20 m. 
In the last 5 years Doppler surveys to provide basic mapping for geophysical surveys were per 
formed by covering the area with a grid-iron pattern of Doppler lines about 1 /4 mile apart with 
a few braces to provide the necessary rigidity. In one job Doppler instrumentation yielded a pla- 
nimetric accuracy of some 300 yards. In Southern Nigeria flight missions are being performed 
using a combination of Wild super-wide angle infrared photography, Zeiss statoscope and a Wild 
horizon camera which takes four horizon photographs on 35 mm film with 34 mm focal length. It 
is anticipated that the horizon camera will yield accurate results if the atmospheric conditions 
are good as found in Tanganyika and Nyassaland but not in Nigeria. - With regard to required 
time and costs for aerial triangulation with auxiliary data little information is available. Hun - 
tings Surveys states that about 1 1 /2 hours instrumental time and about 1 1/4 hours (exclusive 
electronic computer time) for adjustment per model is required, and that these times are about 
the same whether or not auxiliary data is used. 
India : 
The available information reveals that aerial triangulation with auxiliary data is not 
used in this country. 
Iran : 
From the available information follows that in this country no aerial triangulation with 
auxiliary data is performed with the exception of the job performed by Huntings Surveys (see 
Great Britain). 
Japan : 
In this country aerial triangulation with auxiliary data is not used due to a dense natio 
nal geodetic triangulation network (points at intervals of appr. 4 km., and at intervals of appr. 
2 km in flat areas with IV. order triangulation augmented by a I. and II. order traverse net - 
work) and due to an equally dense I. and II. order leveling network. Since the required accura-