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3D-GIS of IIRS campus using ARC-view
E. V. Anoop
College of Forestry, Kerala Agricultural University
Vellanikara, Thrissur 680656
anoopev@rediffmail.com
GIS allows us to study and understand the real world process by developing and applying manipulation analysis criteria illuminate under lying trends in geographic data, making new information available. A GIS enhances this process by providing tools which can be combined in meaningful sequence to reveal new or previously hidden relationships within or between the data sets, thus increasing better understanding of the real world.
A continually varying surface can be represented by isolines (contours), and these contours can be effectively regarded as sets of closed nested polygons. While, sets of isolines are very suitable for the display of continually varying surface they are not particularly suitable for numerical analysis or modeling. So other methods have been developed in order to be able to represent and to use effectively information about the continuous variation of the attributes (usually altitude over space).
Any digital representation of the continuous variation of relief over space is know as digital elevation model (DEM). A digital elevation model is an ordered array of numbers that represent spatial distribution over elevations above some arbitrary datum in the landscape.
There are various structures for DEM in use. As such none of the data structures satisfies all requirements. One has to look for the suitable type depending upon the purpose. Commonly used structures for DEM are: (a) Line Model (b) Triangulated Irregular Network (TIN) (C) Grid Network.
The Triangulated Irregular Network (TIN) is a system designed by Peuker et. al. (1986) for digital elevation modeling. The TIN model is a vector topological structure similar in concept to the fully topologically defined structures for representing polygon networks with the exception that the TIN does not have to make provisions for islands or holes. The TIN model regards the nodes of the network as primary entities in the database. The topological relations are built into the database by constructing pointers from each node to each of its neighboring nodes.
By analysing a digital elevation model, highly useful products can be derived, which are application in various fields. Few of such products are contour maps, line of sight maps, line of sight maps volume estimation by numerical integration, maps of slope, convexity, concavity and aspect, shaded relief maps, drainage networks and drainage basin delineation etc.
The objective of the present study was to prepare a 3-dimensional Geographic Information System (3-D GIS) of the Indian Institute of Remote Sensing (IIRS) campus located at Dehradun. It was also aimed at producing a DEM of the campus and conduct various surface analysis and produce products such as slope map, contour (interpolated) map, aspect map, hill shade map etc. A profile analysis for a proposed road in the campus was also envisaged.
The study area, IIRS campus is located at 4 Kalidas road Dehradun, in Uttaranchal State. The total area of the campus is 10Ha. The topography of the area is plain with few gully structures. The vegetation is of the scrub type with few planted avenue trees and scattered forest tree species and bamboos.
Materials and Methods
Procurement of data
The 3D model of the campus was prepared, based on a survey map of the campus. Various features such as contour lines, buildings, roads, walls, fence etc. were available from the map. Other details such as distribution, height and species information of trees height information of various structures were collected directly through the field study. Digital photography of buildings and procurement of video files for the purpose of hot linking were also done.
Interpretation of data
For the interpretation of the data, a preliminary investigation was conducted in the field. Accuracy of various themes were checked and necessary corrections made. As the survey map was prepared during 1992. Many new additional structures were added to existing map. As the survey map was of multi-featured nature, it was necessary to isolate various themes through tracing, for carrying out proper digitization.
Data entry and digitization
In order to obtain accurate results, tablet digitization by using PC/ARC INFO version 3.5.1 was followed. Various layers that were digitized are as follows: 1. Contours 2. Buildings 3. Roads 4. Walls 5. Fence 6. Lawn 7. Trees 8. Drains 9. Power Line 10. Telephone Line and 11. Internet Line.
After the digitization of various layers, the planar map was transformed from screen coordinates to UTM, and was exported to Arc View 3.1 as arcshape files. Further processing was done in Arc View. Attribute data such as contour heights, building heights and names, wall heights, tree species and heights were added to the data files of the respective themes. In addition, new fields for images and videos were added to the data file of the buildings theme for the purpose of hotlinking. For hotlinking video files new scripts were written using avenue. The Triangulated Irregular Network (TIN) was created from the contour map. Various thematic layers such as roads, walls, fence, lawn, trees, drains, power line, telephone line, internet line etc. were then overlaid with the TIN.
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