Consultant, Land Information Technologies,
J-94, South Extension – Part One
New Delhi – 110049.
Tel: (011) 462 3106
Conventional aerial photography (format 23cm x 23cm) has been practised in India for the last 60 years or more. There are three agencies in India which carry out aerial photography, namely, National Remote Sensing Agency (NRSA), Hyderabad, Air Survey Company, Calcutta and the Indian Air Force. The traditional format is quite all right if the project area is large and mapping is the main objective.
Of late, however, a number of requirements of land information pertaining to small areas like jhuggi-jhompri (JJ) clusters, unauthorised construction etc have become predominant, specially, for the urban administrators and planners. The information which is almost techno-legal in nature is required in a short time. It is very useful for taking strip photography of a highway corridor. The project authorities cannot wait to commission large agencies because the lead-time for an aircraft to come, for instance, from Hyderabad to Delhi is undesirably high. This also becomes too costly in case the area is insignificantly small say a jhuggi cluster covering an area of covering an area of ½ km x ½ km. Prof. Misra in collaboration with Prof Juppenlatz of ITC, Netherlands introduced of the SFAP technology in India. The Rohini Project of DDA, Chandigarh and Haridwar were photographed using Small Format Aerial Photography.
The liberalisation policy in India has provided a big fillip to the highway and transportation sector which deservedly gets the top priority amongst infrastructure related projects. Getting proper physical information for planning the highway related projects still remains a major bottleneck and causes major delays. This is primarily due to the utilisation of the traditional surveying technology of field-oriented surveys. In a specific case, the cost of marking the centre line of proposed alignment, cross sections and preparation of acquisition plan is quoted to about Rs.20, 000 + per kilometer. Small Format Aerial Photography (SFAP) is a proven technology through which, it is visualized to reduce the cost to more than 50% of the conventional method. SFAP is not only cost-effective, it is also highly time-effective, technically accurate and verified in office.To get an idea on the national scale i.e. for highways of 40,000 km, the saving to the national exchequer is likely to the extent of (30,000 x 10,000) 30 crore.
Small Format Aerial Photography
In SFAP, a simple method of taking aerial photography has been designed. Instead of large and conventional format of 23cms x 23cms, an ordinary/commercial camera of 35mm or preferably 70mm format is used. The film is also ordinary film (black & white or colour) which is readily available in the market.
The camera is taken aboard a single engine, small aircraft of low cruising speed (also helicopter). The photographer uses the camera in a hand-held mode. In some cases, a simple modification is done in the aircraft by creating a hole and the camera is fitted in a suitable mount. The photography is done with 60% overlap so as to provide a three-dimensional view of the terrain.
All aerial photography including SFAP is governed by Aircraft Rules. Defence Security clearance is necessary before any flying can be undertaken in India. In case all procedures/requests are according to the rules, the security clearance takes from 1½ month to 2 months. Even after the aerial photography is done under the supervision of the security officer, the exposed film is subjected to the security checks.
Option 1 – Through Visual Inspection of Photographs
- Landuse in the corridor
- Extent and type of vegetation/trees, density of vegetation
- High tension/low tension, telephone poles
- Topography; contours can also be obtained from overlapping photographs in case precise (metric) camera and photogrammetric techniques are utilised.
- Built up areas in the corridor.
- Rough plan of roadside village abadi (built up) area.
- Ribbon development, if any. Unauthorised structures
- Railway crossings
- Culverts and their catchment areas, cross- drainage sites.
- Towns astride the road (partial)
- Bridges and proposed sites (can be seen on 1:2000 enlargements)
- Water bodies/tanks in or near the corridor
- Water-logged areas, denuded land and other environmental information
- Rock outcrops, quarry sites
- Geological/geomorphological hazardous areas
- Acquisition plan on 1:4000 scale (equivalent to cadastral/revenue maps).
- Condition of the road surface
- Sites for social forestry and plantations by the side of the highway
- Sites for construction materials
Option 2 – Through Photogrammetric Processing of Photographs For this option, one has to use metric–camera, preferably, with reseau marks. Hasselblad MK-70 and Rolleimetric 6006 are such cameras which have been used for precise photogrammetric work by the author.
In addition to what we get from option one, longitudinal and cross-sections along with the elevations/spot heights, which help in generating the Digital Terrain Model (DTM) of the highway can be obtained after photogrammetric processing.
Products and Services from SFAP, in general
General Products (Option One) The products which can be obtained through SFAP are:
- Negative film on scales of 1:10,000 to 1:30,000. The positive postcard size enlargements from negative film enlargements are produced at the project-specific-scale of 1:4000, or in some selected places, upto 1:2000 scale.
- The enlargements and postcard size enlargements will have overlap in the direction of flight. The overlapping photographs when viewed under a stereoscope can produce three-dimensional optical model of the ground.
Photogrammetric Products in Special Cases (Option Two)
Photogrammetry implies precise measurements on photographs. In this option, the photography is done with the help of a precise (metric) small format camera. The overlapping photographs are mounted on a special machine called photogrammetric-plotter which can handle SFAP. The products which can be obtained, after due photogrammetric process, are as follows:
- Digital Terrain Model (DTM) with (any) desired density of ground points covering a corridor of ¼ km on either side of the centre line. DTM will be able to generate longitudinal-section and cross-section at desired intervals through software.
- Acquisition plans (map) of the strip of ground alongside the centre line of road on 1:4000 scale. 1:4000 is generally the scale of revenue/cadastral maps.
Note: The present practice is to take a strip of only 100 metres width for producing DTM
Estimated Cost of SFAP per 100 kms (without field visit)
Cost can be broken into sub-activities which are as follows:
- Hiring of aircraft/helicopter
- Cost of film + processing
- Cost of postcard size enlargement of whole film
- Cost of large scale (1:4000) enlargement @ Rs.400 per enlargement, at selected places, (10% of length)
- Cost of tracing details for producing acquisition plan (cartography)
At an average working cost, it comes to about Rs 3000/- to Rs 4000/- per km.
Photogrammetric Option (A stretch of 100 kms of highway is assumed)
Field surveying is required to provide control points. Major activities are as follows:
- Cost of flying (aircraft or helicopter)
- Field control by theodolite traverse, and/or Global Positioning Systems (GPS) for 100 kms.
- Cost of photogrammetric processing including stereo-analytical-digitisation (triangulation) @ 5 models/day or 5 km/day at 1:20000 negative scale
- Photogrammetric plotting @ 4 models/day, for mapping of acquisition plans on 1:4000 scale
- Cost of photogrammetric option (full physical details + contours at 2 metre contour interval) is Rs 8000/- to Rs 10,000/- per km.
Time for SFAP operation:
- Flying mission per 100 km about 2 days
- Photo/Photogrammetric Processing 25 to 30 days
Traditional surveys generally take about 4 to 6 months.
Conclusion
The aerial photography and photogrammetric options provide the planner a good alternative for the physical inputs. The records in the form of aerial photography (SFAP) are permanent. Inspite of the impediment due to the defence security, the technology of SFAP is worth trying with a view to gain major advantage of productivity i.e. cost, time and reliability —— less than one third in cost, time and, of course, reliable.
