INDIA 5 
IV. PHOTOGRAMMETRIC MAPPING 
i. Instruments.—The aerial cameras used for survey photography in India during the period 
1960-64 are as follows :— 
Table 4.—Aerial Cameras used in India during 1960-64 
Manufacturer 
f 
in cm 
Size 
in cm 
Type 
Williamson Ross 
15 
23 X 23 
Eagle IX Mk. II 
Williamson Ross 
30 
23 X 23 
Eagle IX Mk. II 
Wild 
11-5 
18 X 18 
RC 5(a) 
Wild 
21-0 
18 X 18 
RC 5( a ) 
Wild 
11-5 
18 X 18 
RC 8 
The following photogrammetric instruments have been used in the Survey of India during the 
period under report:— 
3 Williamson Ross S.P. 3 Multiplex 
2 Zeiss SEG V Rectifiers 
14 Zeiss Radial Secators RS I 
4 Zeiss Radial Secators RS II 
2 Zeiss Sketchmasters 
8 Wild Autographs A7 
16 Wild Autographs A8 
44 Zeiss Stereotopes 
4 Zeiss Parallax Convertors 
2 I.T.C. - Jerie Analogue Computers for Block Adjustment. 
Seven Wild Aviographs B8 have just been received and some more Wild Aviographs B8 and 
Kern PG 2 plotters which are on order are expected shortly. 
2. Methods.—In the Arundel method of graphical air survey, the scale of photography is normally 
kept about two times the desired scale of the map and the air survey also is carried out on twice the 
scale of final map. The reason for this practice was to minimize the errors of graphical air survey 
by reduction. Another practice for increasing accuracy is to carry out the completion surveys by 
ground verification on blue-prints obtained from the air survey sections where the details and con 
tours are further checked from plane-table fixings. 
The employment of photogrammetric instruments altogether changed the pattern of completion 
surveys. The accuracy of photogrammetric survey being higher than that of ground survey, no 
ground check was necessary as such. If the details which are not easily interpretable on aerial photo 
graphs and information like classification of roads, perenniality of rivers and place names, etc., are 
ground verified and marked on the aerial photographs before the photogrammetric plotting is com 
menced, it has been found that the efficiency and accuracy of the photogrammetric plotting is im 
proved to a great extent as the operator finds all the relevant information readily available and he 
does not have to spend time on the expensive instruments in interpreting unfamiliar object images. 
The speed of ground completion survey is also increased by the use of aerial photographs as 
these serve as a more up-to-date and easily readable map for the movement of the ground verifier 
than the blue-prints of the air survey sections. From experience in India, it has been found that 
except for very large scales of survey, it is always more economical and efficient to carry out ground 
verification of aerial photographs prior to photogrammetric plotting.