Dr. Aniruddha Roy
Navayuga Spatial Technologies Pvt. Ltd.
Email: [email protected]
Delhi State Spatial Data Infrastructure (DSSDI) is a project undertaken by Delhi administration in 3D geospatial data creation and management. The project has been executed by Navayuga Spatial Technologies as a turnkey project and supervised by the Survey of India conforming to national mapping standards and specifications. The datasets have been handed over to Geospatial Delhi Ltd, a geo-knowledge company formed under Government of National Capital Territory of Delhi (GNCTD) for its effective usage in governance and public domain as per the guidelines of Delhi GeoSpatial Act, 2011.
Need for Delhi SDI
The Delhi administration felt the need of large scale accurate spatial datasets covering 1500 sq. km area for planning and monitoring of various developmental activities and providing citizen-centric services. In order to ensure the updated procedure in the spatial and attribute datasets, the need to create a geospatial act was felt to mandate keeping the data and services updated and current, conforming to the emerging technologies and standards.
In the past, several government departments developed spatial datasets with 2D geometry pertaining to their domain but the datasets from different organisations follow different standards in terms of scale, projection, accuracy, content and format. The objective of the project was to build the 3D spatial datasets using modern technologies. The Project Directorate gathered inputs from each participating line department and built every component of the project from the scratch. The base map was created through the photogrammetric procedures on a large scale (1:2000), using aerial photography substantiated by various kinds of field surveys, namely topographic survey, property survey of dwelling units, underground utility surveys (including water, sewer and energy utility ) and field photography in order to generate textures for the 3D models of the buildings. At the peak of the project execution, close to 1000 field surveyors were deployed. The different components of the DSSDI Project are shown in Fig. 1.
The project’s technical team established the control network through GPS survey in the field. In a secured facility of Survey of India office building, about 120 production staff of Navayuga, under supervision of Survey of India personnel, carried out photogrammetric and GIS data capture and extract processes of spatial features supported by integrating the inputs from more than 30 different line department’s attributes and field topographic datasets.
From the aerial photographs, 3-dimensional coordinates were calculated for real-world elements through establishment of the mathematical relationship between aerial photographs, camera and the ground through aero-triangulation process. The digital elevation model (DEM) was created for the entire area with high accuracy. Ortho-mosaic of the aerial photographs was generated by removing the distortion caused by camera optics, camera tilt and differences in elevation, maintaining uniform scale and true geometry.
Fig. 1: Components of Delhi 3D GIS Project
Fig. 2: GPR Survey with Terravision equipment
Fig. 3: Schematics showing the underground utilities
In the field, the utility survey was carried out through state-of-the-art terra-vision GPR equipment for capturing details of all underground utility lines up to 4 metre depth below the surface of the ground. Another 3D component relevant to the subject was 3D pictorial GIS. It comprised organising texture-photo based GIS for the buildings mapped from the aerial photographs with 3D topology so as to provide 3D visualisation. For this activity, field photography for the buildings textures was done and processed on the production floor through the 3D workflow. The 3D workflow is a highly efficient, custom workflow that was used to generate 3D models and 3D terrain databases in a production setting. Spatial data acquisition was carried out for feature geometry data, such as stereo compilation results for buildings and other 3D objects, as well as collection of ground level texture images from GPS-enabled digital cameras.
The workflow for the 3D pictorial GIS can be broken down into four main phases with unique goals, data inputs and software components.
- Process data: Processing of the stereo compilation was done to achieve optimised 3D geometry suitable for building 3D models. It also included processing of GPS-enabled field photographs that were used as texture sources for 3D objects.
- Build models – The texture imagery, acquired through GPS-enabled photographs, was used to extract and apply textures onto the faces of the individual 3D model. Advanced modelling was done to remove the bad textures which resulted from the field photography owing to obstructions, cut-offs etc. Mosaic of the images provided the generation of the final model. Different levels of details (LOD) in 3D models were created based on project requirements.
- Construct 3D scene –Textured 3D models, a terrain surface (DEM), geo-referenced imagery and other data sources were combined to build a 3D scene, or 3D terrain database, which represented a single, integrated virtual environment.
- Visualise / Analyse – The 3D scene constructed above was loaded into a visualisation environment in OGC complaint software Citysurf, which enabled to provide feeds for 3D Pictorial GIS to ten monitoring centres set up in various locations of Delhi. The sample data provided by Survey of India is shown in Fig. 5 and Fig. 6.
Fig. 4: 3D Pictorial GIS workflow process
Fig. 5: Overview of the 3D building models
Fig. 6: 3D Pictorial GIS of buildings
An SDI, based on open standards, provides a platform (data interfaces) for the development of “apps” for urban decision support. In order to integrate the building textures into the 3D models and then share with the user community, OGC approved KML version 2.2 was adopted. KML is an XML-based programming language, originally developed to manage the display of geospatial data in Google Earth. However, based on its growing popularity, it is now being supported by the majority of the GIS software OEMs. Provisions are being made for using key standards like CityGML and CSW-ebRIM which developers can access in the SDI and readily develop applications to deal with all manners of urban problems, including emission reduction, building ventilation, solar heating and power generation, green roofs and walls, crowding and traffic management.
Access to a comprehensive, large-scale spatial database comprising more than 350 spatial features integrated in an enterprise database is being provided to 30 functional line departments of the government from a control centre through secured lease line. The information on underground utilities comprising water, sewer, power lines etc is also being used now by engineering departments for all excavation planning and execution activities through an enterprise application – PDM (plan, dig and monitor). The hardcopy maps printed out from the project database are being used by various departments for their routine activities. Citizen-centric services will soon be provided through a public geoportal using Navayuga GeoPortal software solution.
In DSSDI, a 3D GIS project, citywide mapping coupled with enterprise GIS applications supported through metadata query process has been developed in Delhi. Support from the Delhi administration and Survey of India, besides cooperation from all line departments, has led to the successful completion of this project. The maintenance for the data and applications for next five years started from July 1, 2012. SDI does not mean everyone will be provided with all information, but that the information we visualise and operate on, be consistent for everyone. The data and design model developed under the aegis of Survey of India forms the foundation for the future large scale 3D mapping projects.