INDIA 3 
arried out, Stereotope has been employed for plotting on scales 1 : 20,000, 1 : 25,000 and 1 : 50,000 with 
| contours at 10 and 20 metres vertical intervals. 
  
  
| . . . . : : : : : : : 
—— | Aerial Triangulation.—Aerial Triangulation adjustment is still being done graphically. 
ARES | Lens distortion is eliminated by using compensation plates. Uniform film shrinkage is corrected by 
| correcting the Plotting Principal Distance. Uptill now, for all types of work, diapositives on film 
T | have been used. 
During the years 1958-59 Aerial Triangulation on A 7 for about 50 strips measuring about 
1,800 Kms. in length was carried out. Particulars are given below :— 
| | | 
nly vertical Map scales . . | 1 : 50,000 | 6” to 1 mile | 3” to 1 mile 1: 25,000 
Photo scale. . oe 1: 50,000 | 2” to 1 mile | 2” to 1 mile 1: 40,000 
| Purpose  .. .. | Plan and height control, or | Plan only | Plan and | Plan and 
| plan by slotted templet | heights heights 
assembly and heights by | 
Aerial Triangulation | 
  
  
  
  
Camera used | RC 5a WA | RC 5a 1C 5a | RC 5 
rgest scales Eagle IX wa | wa‘. | WA | wA 
ng 1: 6,000 | 
Contour Interval po dl 20 m. | 5 ft. 10 ft. F 10m. i 
Accuracy achieved for | + 2:5 m. | Heights by | + 1-7 ft. + 2 m. 
heights for an average | | levelling | | 
strip of 12 models | | 
) 
Out-turns.—Photogrammetry has increased the out-turns of large scale mapping by 2 to 3 | 
times as compared to ground survey methods. The primary purpose of equipping the Department dl 
with Photogrammetric instruments is thus being achieved beyond expectations. A glance at the table "I 
below confirms it :— | 
| 
Sinn | Out-turn by Photo- ; i 
Scale of Survey Out-turn by ground | grammetric methods Approximate per cent 
: methods per man-month ; increase in out-turn 
| per man-month 
d 
1:50,000 .. ve 20 sq. m. | 40 sq. m. 100%, 
V.I. of 20 m : 
1:25,000 .. . 5 to 6 sq. m. | 12 to 15 sq. m. 150% 
V.I. of 10 m | 
1:10,000 .. i 1-5 sq. m. | 4 sq. m. 170% 
| by Aerial V.I. of 5 ft. | 
necessitates | 
iangulation | 1:3,960 .. s 200 Acres 600 Acres 200% 
| depending | V.L 8 ft. 
| 1:1,000 .. ‘e 20 to 25 Acres 90 Acres 350% 
V.I. 2 ft. 
), 1 : 25,000 
ervals. 
  
Future Plans.—India, being a vast country, requires a complete map cover, mostly, on small 
10,000 and | scales, with special surveys on large scale to meet other demands. The latter has not presented us 
with much difficulty as the 1st and 2nd order instruments are more than adequate to cope with all