• 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.

• 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.