+ 
The large areas covered are an index of the rapid pace of development in the country 
and of the awareness of various disciplines concerned with earth resources and of the benefits 
of aerial photography. 
Radial Triangulation.—Extention of control was carried out by combination of 
slotted templets and/or stereo-templets over large areas basically for the purpose of up-dating 
and revising the existing map cover on the scale of 1: 50,000 and occasionally at the scale 
of 1:25,000. In most cases photography on scales ranging from 1 : 40,000 to 1 : 60,000 was 
utilised. Accent for surveys on these scales was on the insertion of new planimetric detail 
- and correction of out-dated information. The table below indicates the work done in this. 
  
  
regard :— 
Scale of com- | Approximate scale No. of | Area in | M 
aoc | | ethod 
bination | of photography | photos | sq km 
1 : 50,000 1 : 40,000 to | 6,800 |  1,42,500 | Stereotemplet/slotted 
1 : 60,000 | | | templet 
1:25.000  1(4)1:30,000t0. . | 500 4,800. | ditto 
1 : 40,000 | | | 
(b) 1: 50,000 to | 2,100 | 30,500 | ditto 
1 : 60,000 | | 
1 : 15,000 1 : 15,000 Li 4150 400 | Slotted templet 
  
Aerial Triangulation.—Almost all productive work carried out for the department 
was based on control obtained by classical aero-polygon method. Adjustments were carried 
out either by graphical or by the ITC Jerie block adjustment methods. This classical method 
is, however, now being increasingly replaced by independent model observations adjusted with 
the help of electronic computers. Strip formation and block adjustment in this analytical 
work are carried out using programmes widely known as NRC-9695 and NRC-7906 developed 
bv Professor G. H. Schut of the National Research Centre, Canada. 
Recording of photograph co-ordinates and preliminary investigations are carried out 
with the help of EK-5 and EK-8 automatie co-ordinate recording devices and electronic desk 
calculators. Efforts are in hand to develop similar machines indigenously. 
The table below indicates some of the more important tasks for which aerial triangula- 
tion and its adjustment were carried out :— 
Nuniber of strips with 
Approx. LA | : 061] : | 
scale of | No. of | Areain | : 
hotography models sq km | Method of Adjustment 
photography more than 20 to 10 less than | | | 
  
20 models models | 10 models | - | | 
^ 11500 | - | 10 | 2 | 130 | 350 | Combination of stereo-templet 
| | | | | and height by ITC Jerie method 
1:25,000 | ps | 5 | | 70 | 550 Programmed for IBM 1620. 
1: 25.000 | | 4 | 30 | 230 ditto 
1 : 65,000 2 | 6 | 7 | 160 | 70 ditto 
1 : 40,000 qu] 11 | i | 280 | 3,000 ditto 
| | | 
1 : 40,000 16 | i | er | 540 | 6,500 | ditto 
| | | | 
1 : 40,000 3 | 3 | 2 | 150 | 3,000 ditto 
1:40,000 | 11 | + | iE | 250 | 3,000 | ditto 
1:25,000 | am goo] À st {i 1,500 ditto 
1: 30,000 : | | | | 
and smaller 77 389 | 374 | 9,658 | 1,89,500 | Graphical/analytical