New Delhi: Delhi Development Authority plans to conduct a photogrammetry survey using a differential global positioning system (DGPS) to create a three-dimensional map of four green spaces in Hauz Khas in south Delhi. Among them are the district park opposite RK Puram, Rose Garden, Master Plan green area and sports field and the Master Plan green area with the picnic hut.DDA plans to complete the survey, for which it has invited tenders, by 45 days and has sanctioned Rs 14.6 lakh. Photogrammetry is a technique that uses photographs to create three-dimensional models of objects and landscapes. It involves capturing images, often from multiple angles, and then using specialised software to process and analyse them to extract measurements and geometric information. The exercise usually involves aerial photography using drones or aeroplanes, or terrestrial photography from fixed points on the ground.DDA officials hope the mapping will demarcate the boundaries of the parks, land contours, structures and actual areas where development can be planned in the future. “While similar methods were adopted at other places, including the Yamuna floodplain, the survey helps us understand the area in detail, its elevated portions, waterbodies, poles and other structures,” said an official. “The survey findings simplify the process to carry out development and are also helpful in checking encroachment.“While GPS and DGPS both use satellite signals for positioning, the latter offers significantly higher accuracy by incorporating a network of ground-based reference stations. GPS typically provides accuracy in a range of metres, while DGPS can achieve centimetre-level accuracy.The agency selected for the work will be responsible for a detailed photogrammetry survey, preparing orthophoto maps and submitting soft copies in a geographic information system. “The agency shall also provide on-site basic training for GIS software,” DDA’s project document stated.The orthophoto maps are geometrically corrected aerial photographs or satellite images adjusted to remove distortions caused by camera tilt, lens and terrain relief. The orthophoto maps show geographical parameters like longitudes and latitudes in 3D views and all permanent features like structures, bore wells, roads, electric and telephone poles, high tension lines, mast lights, tracks or paths, drains, sewers, trees, etc.Over 16,000 acres of green area in Delhi fall under DDA’s purview. This includes 10,400 acres spanning 729 public parks, 21,000 acres of biodiversity parks and 3,500 acres of the Yamuna floodplain, which are at various stages of restoration.
