Methodology In a conventional map, which is in two-dimension, the height information is shown in the form of contours. However, the elevation of each object in the map cannot be shown unless the elevation of each object is measured and then incorporated in the map. The calculation of elevation of each object is either done through conventional survey methods or through aerial photography, combined with GCPs (Ground Control Points) to generate 3D models on digital machines. This technique is time consuming and cumbersome. In the present pilot study of Chandni Chowk, in addition to the existing technologies, video mapping has been incorporated to its best use. The data and information required for building and maintaining a 3D GIS include:
Thus, apart from a large number of ground control points, the ALTM (Airborne Laser Terrain Mapping) data of Delhi (see box) was used. ALTM offers very high accuracy, in terms of height, which can generate very high resolution digital elevation model and/or contours of 10-15cm spacing, which is otherwise not possible using the conventional aerial photography or any other ground methods. In brief, the methodology adopted is firstly to provide GCPs, fly an ALTM mission and map heights at every 10-15cms. Taking the height control points, adjust it to the scale with high resolution satellite image and make it into an ortho map. On this ortho map, take the video of the area, and the ortho map and stitch them up.  Fig. 3. GCPs Used for Georeferencing . This will result into an live 3D GIS map. Since the stitching is done digitally and the map used is ortho, the height information in the final map is fairly accurate. The basic requirements for the 3D GIS model are,
The study area (Figure-2a) for the current pilot study comprises the Delhi City Zone Area I and covers 20 sq. km area. The area lies between 77o12’30”E to 77o15’30”E and 28o35’30”N to 28o42’30”N covering Chandni Chowk, Red Fort, Darya Ganj, Sadar Bazar,Tilak Bridge, Pragati Maidan, Hauz Khas, Civil Lines, Minto Road, Nai Sarak etc. The transportation network of the area is shown in Figure-2b. The GCPs used in the study for LiDAR is shown in Figure-3. Putting to use The generated 3D GIS of the area was put to use with collection of thematic information on the residents, buildings and availability of different utilities. As the study was done in a pilot mode, only 10,000 samples were taken from the study area for which every data on people, housing and utility was collected and analysed. Data on property tax calculation was also incorporated which resulted in automated property tax calculation, devoid of any ambiguities. After making the database, in the area of 20sqkm, every inch of detail can be seen. The collected data can further be used, if it is continuously monitored with additional information from the information tracking cameras (Figure-6a and 6b).  Fig. 4 2D GIS of Chandni Chowk and Fig. 5 Resultant 3D Model |