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Physical information inputs for planning agencies

Aug 2005 | Comments Off

	Proposed Design of technology-mix based on GPS and Photogrammetry

The environment of a Municipal Information system has undergone a sea change over last few years. Couple of years back the requirements of information system was designed and projected primarily from the planners community. They were satisfi ed if the physical information was supplied on a scale of 1:5000/ 1:10,000.

Presently the demands are coming from urban engineers involved in detailed design of water supply and sewerage systems, traffic and transportation (including fire and police), electricity and power and revenue authorities that are concerned with the land/ property related matters. Comparatively new entrants are the professionals from the telecommunications (diggers for fibre cables!) and other utility – infrastructure personnel, who have started looking at the third dimension
of the town (heights of buildings) for mobile cell communications. There are hosts of other users who need accurate urban information.

The upshot of all the above information is that the Municipal Information System (MIS) which is being designed today must cater to all the future requirements which should be presented in the most friendly manner. What is mentioned above is the perspective of the proposed design incorporating the optimal use of various technologies in the realm of modern geomatics. The digital database of physical information will, in fact depend on the judicious combination of technologies of photogrammetry and Global Positioning System (GPS) which will form the ultimate Geographic Information System (GIS) of the Metro town.

Requirements and Scale Matrix of Different users

The table 1 indicates the needs/ functions in terms of scale of maps and information on elevations. For digital maps the scale depicts the density of information and inherent accuracy linked with that scale.

Determination of Scale, Elevation and Contents of Database

A glance at the table 1 clearly indicates the design of the database which should cater to the present and future needs of the various stakeholders (users) of the database. The database should also take care of the various ‘attributes’ as defi ned in GIS. For example in housing function, apart from the spatial location of the house, the ownership, tax status, number of inhabitants, usage (residential/ commercial) etc should also be stored in the Database for the benefi t of end user of GIS.

It is very evident that all the required information need not be built as one project. The urban database can be designed on the ‘evolved’ basis. The priority information needed by most of the users can be collected fi rst. The remaining information and attributes can be acquired in the phased manner. The direction of thinking has led us to first create the essential information through proper aerial photography, field surveys for ground controls and Photogrammetry which will act as foundation to link any other spatial information to be collected in subsequent phases. As a word of caution, the control technology in the field should be very reliable and accurate right from the beginning.

Objectives of the Design

To establish computer based (digital) database for an urban area or a metro area utilizing the modern technologies of: Aerial photography, Control technology of GPS Photogrammetry; Orthophoto and stereo restitution GIS and satellite imagery.

To design the information retrieval system which is friendly to the functioning departments who will utilize the databases.

To keep this database updated to the time cycle of 4 – 6 months.

Design Concepts

Methodology

In particular, we recommend the use of aerial photography, a well proven technology of Photogrammtry, which is productively and commercially being utilized for many urban projects. The modern technology of GPS will go to support the preparation of Digital Database and the processing of Photogrammetry. The basic steps involved in the methodology are described further.

a. Aerial Photography

It is proposed that the whole urban area should be covered with aerial photography on scale of 1:8000. The above scale has been selected in order to produce accurate basemaps up to1:2000 scale. These base maps can also be utilized for urban cadastral purposes (authentic map of property) and for determining the encroachments.

b. Urban vector maps

Urban agencies will be interested in true location of almost all the physical features. Keeping this in view a scale of 1:8000 for aerial photography is proposed as optimum which will be used for producing 1:2000 scale vector maps. The vector maps based on accurate technologies of GPS and photogrammetry only can resist the legal onslaught in any dispute.

c. Vital Role of GPS

Photogrammetry stipulates a minimum number of ground controls points at proper location with respect to the incidence of aerial photographs (model) on the ground. These groundcontrol points are marked very accurately on the aerial photographs and form the first and most important input to the process of photogrammetry. By resorting to the differential GPS for provision of ground control an accuracy of ± 5 cm can be achieved.

As mentioned earlier, the ground control points form the first input to Photogrammetry. In that, these control points are used to orient the aerial photographic model (stereoscopic model) for scale, elevation and accuracy. We wish to identify some ground points in the town which are small in size, peculiar and symmetrical so that these are easily identifiable on aerial photographs. We would like to provide x, y, z control points for photogrammetry. The special requirements, if any, by user agencies for identifying certain fixed points can also be taken care of.

d. Monumentation of Ground Control Points

It is the normal practice to provide some permanent pillars (x, y, and z coordinates) at suitable places in the city which will be most valuable for any future references. These references have a tendencyto crop up in land oriented legal disputes. The permanent pillars also are ideally useful for location of engineering projects on the ground. A suitable design on the survey pillar appropriate to the city and the location of the pillar can be evolved in consultation with the authorities.

e. Photogrammetric processing

This is photogrammetric operation in which initial field control (as mentioned earlier) is augmented by a set of procedures on photogrammetric instruments. The result is that the photographs (stereo models) will have control points at optimum places. These control points obtained after aerial triangulations are used for automatic orientation of models in analytical/ digital photogrammetric instruments before carrying out photogrammetric plotting/mapping. The digitization of all the physical details of the map and elevation is done mechanically while plotting. Thus in present day photogrammetric machines the map output can be obtained as hard copy as well as in digital form.

Digital Database – Contents and Format

The database will have the following information, the list is just indicative and can be modifi ed as per the requirements of Urban Agencies.

a. Physical Information

All topographical features subject to the scale of 1:1000, contours at 1 m contour interval, spot height at 100 m grid, ground control and GPS stations.

b. Buildings

Building roof; Building, heights of buildings, especially high rise buildings; Industry/ Commercial area/ Business sheds; Retaining wall; Chimney; Brick Kiln

c. Road

Metalled/ consolidated road; Unmettaled/ unconsolidated road; Parking; Traffic Island/ Boulevard; Traffic fence; Internal road; Road center line; Roa various/ path; Road Bridge

d. Drainage

Rivers (>3 m wide – 2 lines); Streams (<3 m single line); Edge of drain/ ditch; Canal bed; Canal Bank; Culvert; Well; Lake/ Pond/ Tank; Marshy land/ Bogs