The cutting edge `geoinformation’ revolution

Abstract
The rapid developments in Global Positioning System (GPS) and other geoinformation technologies, especially Geographic Information System (GIS), remote sensing, photogrammetric techniques and World Wide Web (WWW); offers efficient tools for integrated solutions in surveying. The effectiveness of decision-making using Geographic Information Systems (GIS) mainly depends upon availability of up-to-date data. The use of GIS for development and maintenance of an integrated database, shared by many users, eliminates problems of data duplication. The inter- and intra disciplinary integration provides an opportunity for augmentation of real-time data from field, directly into commonly accepted enterprise data structure. The paper highlights innovations in GPS that have revolutionised the way we collect, share and maintain data.

Introduction
The effectiveness of decision-making depends upon real-time data availability, whereas lack of up-to-date planning and social databases, particularly in most developing countries, leads to unguided development. The development plans in most developing countries do not reflect actual field conditions. As a result, officers in local authorities lay a major road passing through a plot of land, actually where an unauthorised slum has come-up. As a result, we are following Building-Occupation-Planning-Surveying instead of Planning-Surveying-Building-Occupation. The development planning without referring to actual field condition and sever delays in resurveying leaves the planning mechanism in danger of not reflecting actual field conditions, which in association with other institutional problems leads to mismatch with unprecedented speed of urbanisation.

Furthermore, survey networks in most developing country are established during colonial rule using traditional measurement and triangulation methods, which were updated using different techniques at different times giving varying accuracy. In addition, many studies have reported that ground survey monuments are vulnerable to displacement or removal due to various reasons, which are reference points for new surveys. The above discussion indicates that the use of traditional terrestrial surveying methods such as theodolite, levelling instruments, Electronic Distance Meter (EDM), and total station have proved cumbersome, time consuming and relatively inaccurate. Above methods and approaches have been dominant until very recently, however, evolution of Global Positioning System (GPS) and innovations in integrating Information and Communication Technologies (ICTs) has revolutionised modern surveying, mapping, navigation and positioning.

GPS
The evolution of GPS has revolutionised the way we measure length, area, height, time, and velocity and this has created new opportunities through out the interdisciplinary world. The GPS system can be divided in three segments – space, control and user segments. The space segment consists of constellation of 24 satellites in six evenly spaced orbital planes, placed in circular 12-hour orbits inclined at fifty-five degree to equatorial plane. The control segment consists of a system of tracking stations located around the world. These stations measure signals from Space Vehicles (SVs), compute orbital data, upload data to the SVs, and then SVs send data to user segment GPS receivers over radio signals. This constellation provides the user with between five to eight SVs visible from any point on the earth. On clear visibility of four satellites, it provides three-dimensional position; X, Y, Z and T (time) on a 24-hour-per-day basis all around the world.

The NAVSTAR GPS is funded by and controlled by the U.S. Department of Defence (DOD), initially to support military applications and later also for civilian uses with certain restrictions (Logsdon, 1992). In addition to NAVSTAR GPS, Global Navigation Satellite System (GLONASS) from Russia and European Global Navigation Satellite System (GNSS) also provides worldwide GPS services (Zarraoa et al., 1998 and Gallileo’s World, 2000). During the discussion in this paper NAVSTAR GPS is referred as GPS unless and until specified. Recently, civilian use of GPS has stretched the limits of technology to explore applications in georeferencing, positioning, navigation, and for time and frequency control using GPS receivers. GPS satellite signals cannot pass through buildings, metal, mountains, or trees. Therefore, in locations where at least four satellite signals with good geometry cannot be tracked with sufficient accuracy, GPS is unusable.

GPS can provide Precise Positioning Services (PPS) and Standard Positioning Services (SPS). The PSS is limited to military uses with a 22-meter horizontal and a 27.7-meter vertical accuracy, whereas the SPS for civilian use can provide 100 meter horizontal and a 156-meter vertical accuracy. Prior to 2nd May 2000, accuracy of PPS was degraded for civilian uses by the use of Selective Availability (SA). With Selective Availability in operation, accuracy in point positioning is only 10 to 20 meters, which is not suitable for most mapping purpose. The removal of SA gives much higher accuracy for standard positioning, as good as 20 meters horizontal and 30 meters vertical (Dana, 1997). The issues regarding removal of SA represents different views, some users believe that now it is possible to achieve sub meter accuracy by averaging readings, however, Wadhwani (2002) argued that there is possibilities of multiplying the embedded errors in inaccurate readings (for further reading see Bennett, 1991 and Jacobson 1991).

GPS errors are a combination of noise (instrumental deformation), bias (SA, clock error, signal delays, multipath signals), and blunders (hardware and human error). The error due to noise could be around 1 meter, whereas bias error can amount from 1-10 meters and above all these, blunder error can cause positional difference of hundreds of kilometres (Dana, 1997). Furthermore, it is important to note that the radio signals from SVs travel at the speed of light, 186000 miles per second, and the delay of even a 1/100th second due to any of these errors can put the accuracy off by 1860 miles (Leick, 1992). After removal of SA the cumulative effect of these errors can be expected to be approximately 10-meter, significantly better than the 100-meter under SA (Harrington, 2000). The effects of bias errors can be overcome with innovative developments of Differential GPS (DGPS). In DGPS an additional reference receiver is used to compute corrections in real-time or later as post-processing, which can provide batter precision.

Potential developments
For hundreds of years, traditional surveying has been constrained with required line of sight, but after evolution of GPS, one does not need to maintain clear line of sight. GPS offers all weather surveying with a clear view to the sky without need to traverse across intervening land or around obstacles. Developments in GPS occur at an unbelievably rapid speed, which can be appreciated by looking at the speed of GPS innovation. For example, observation time has been shortened from 5 hours to 5 minutes, and most notably the accuracy level has improved from couple of centimetres over a few kilometres to a couple of centimetres over 10,000 kilometres. After removal of SA, single point positioning accuracy of 10 meters can be obtained (GPS World, 2001).

However, GPS technology cannot be seen as a panacea, its potential can be realised while integrating it with other geoinformation and communication technologies for cost-effective solutions. There are several ways to consider integration of GPS into GIS environments, which can be categorised as data focused, position-focused and technology-focused integration (Harrington, 1999). The following discussion provides rationale for integrating GPS with other geoinformation technologies.

Surveying
The integration of GPS, GIS and remote sensing offers efficient solution to large-scale surveying. Patel (2002) had articulated a case for integration of theses technologies, which provides opportunities for economic geo-referenced spatial data augmentation techniques. In particular, the use of GPS in land surveying proved a great efficiency and accelerated data acquisition with required accuracy for topographic and cadastral plans. For example, the use of GPS in CAD environment in Morocco suggests considerable time and resource savings to develop cadastral and topographic maps with relative accuracy of 10cm (Elayachi et al., 2001).

Geospatial data acquisition
Processing and analysis of spatial information/data presupposes availability of positional data, however most local governments in developing countries do not have adequate spatial data and whatever data is available is outdated. The ability of GIS performance to carry out spatial analysis crucially depends upon quality of data available. This indicates the need for resurvey at a regular interval to capture short- and long-term variations in the field in order to keep the data in real-time. GPS is increasingly used as a tool to input data for GIS, particularly for precise positioning of geospatial data and collection of data in the field. Remote sensing images have been used as a real-time spatial data source, however they require corrections before using in a GIS environment. The process of correcting remote sensing imagery, georeferencing, requires accurate ground control points. Cook and Pinder (1996) and kardoulas et al. (1996) reported that rectification of Landsat TM, SPOT Multi spectral and Panchromatic images became easier by using GPS that eliminate time involved in establishing ground control points. Gao (2001) also preferred non-differential GPS technique for image rectification using ground control points.

Maintenance and updating enterprise database
Managing decay in GIS data due to urban sprawl and regeneration is one of the most challenging tasks in front of local authorities. GPS-based tools for GIS data maintenance have the potential to substantially reduce the cost of reversing decay in GIS database and keep it real-time. In response to continuous process of urbanisation, resurveying is required at regular interval to acquire field data, which needs modification of thousands of features into an enterprise wide database. The innovative hand held GPS receivers with integrated wireless communication technology enable collection and management of large-scale geospatial data using the Internet/intranet. The advantage of wireless modem helps field crew to send new or updated data to a central data processing unit, where quality assurance is carried-out. This helps in rapid turn-around for data that may need to be re-acquired while crew is still in the field. The WWW based local area augmentation system can continuously receive satellite data and supply field data for real-time applications. The real-time map display, editing, post-processing, and conversion are becoming better integrated, more functional and easier to use with pen-based ruggedised field computers.

Improving interface
Another significant development in this technology is improving user interface that facilitates filed-data augmentation by semi-skilled personnel. Furthermore, many commercially available GPS compatible hardware and software allow field data collection directly into GIS database structure, eliminating post-data processing. Graham (2000) reported an extensive survey of GPS/mapping products available today. The availability of commercial mapping software, such as PenMap, allows viewing of multiple raster and vector background maps with user defined attributes. In addition to positional data, attribute data and digital picture or photographs from multiple users can be imported, which creates virtual field-site. It also enables data import and export in GIS format from third-party instruments, including theodolites, imaging devices and laser range finders, creating a true two-way data flow between GIS and GPS products. However, for above-mentioned applications the prerequisite is availability of all data layers in same scale with standardisation of projections and datum. This informs that countries which are in the process of digitising their maps needs to consider internationally accepted cartographic projection for future integration of these datasets with real-time satellite remote sensing images (PCI Manual, 2000).

Real-time post-processing
DGPS corrections were traditionally applied by post-processing, but recently real-time DGPS services using integrated beacon receivers eliminate post-processing that involves more analysis, interpretation and time. One can use free of charge real-time correction signals from the U.S. Cost Guard Services, or subscribe to private companies who offers worldwide correction signals from satellites for annual or monthly subscription charges. Only premium-accuracy services carry a subscription charge. Manson (2000) reported that from mid-2000 three wide-area DGPS augmentation systems (WAAS, EGNOS and MSAS) provides free DGPS correction for the Americas, Europe, and Asia respectively.

Improving accuracy
The navigational applications of GPS typically require accuracy precision in the range of few meters, but engineering applications are demanding much higher precision in the order of centimetres or better. The evolution of differential Carrier-Phase GPS and Real-Time-Kinematic (RTK) surveying have overcome the limitations of DGPS. This has revolutionised GPS surveying with centimetre level accuracy without intermediate reference points up to 30Kms (Dana, 1997). The accuracy and precision of GPS surveying and mapping application have direct correlation with cost. As a rough guide, following parameters should be considered
- Low-cost, single receiver SPS positioning (100 meter accuracy)
- Medium-cost, differential SPS code Positioning (1-10 meter accuracy)
- High-cost, Single receiver PPS positioning (20 meter accuracy)
- High-cost, differential carrier phase surveys (1mm to 1 cm accuracy)
- High-cost, Real-Time-Kinematic with real time accuracy indications (1 cm).

Challenges and limitations
Besides potential of GPS and integrated ICTs, effective use of these system require training, and knowledge of the limitations. There is a potential danger in the civilian use of GPS by untrained users in a new and unconventional approach. The overestimated and misinterpreted capabilities of GPS can lead to lower quality outcomes and loss of time and money, creating disillusionment regarding potential capabilities. For example, GPS integrated GIS data collection do not work everywhere, such as dense tree canopies and urban canyons, especially where there are lots of multipaths around the feature. Mansfield (1998) reported that these problems could be overcome using laser range finder that provide efficient data collection by saving time and money. However, choice of appropriate solution depends upon user’s knowledge. For example, fluxgate compasses in laser range finders are not precise as gyro compasses, adding one meter of error for every 100 meters of distance. In many cases, claims of vendors misguide new users and failure to achieve desired results creates disillusionment regarding available technological solutions. Here it is stressed that user awareness regarding technological developments plays vital importance in light of cost and benefits of choosing appropriate technological solution. Leick (1990, 1992) had raised a question about functionality of the system on the basis of only operational knowledge of GPS - “Is a push bottom knowledge of GPS sufficient?” Further, he suggested inclusion of theory of GPS surveying in college and university curriculum to improve awareness in user community to facilitate rapid diffusion of GPS applications in surveying and mapping.

As discussed above most users in developing countries are relatively inexperience and in dilemma about choice of GPS receivers, available in different specification with cost ranging from Rs. 15000 to Rs. 10 lacs for a single receiver. In the technology driven market, users do not know what they need for their application, making choice of appropriate GPS receivers in question. Here vendors and training institutions play an important role to demonstrate real capabilities of receivers and their limitations for various applications. Particularly, when small users have effective use of receivers for only 20-30 days in a year, it works out cheaper to hire instruments instead of purchasing. Furthermore, service and maintenance of receivers is a problem in developing countries such as India, which emphasise on maintenance support and training of human resources while purchasing GPS receivers. For effective and easier diffusion of GPS applications in India, government needs to concentrate on awareness raising, education, human resource training to improve embedded knowledge of GPS and evolution of facilitating policies as vital vectors.

Another significant issue is surrounding reference datum for GPS signals. The satellite GPS signals provides measurements in World Geodetic Co-ordinates System (WGS84), which is fixed to the earth with its origin at centre of the earth. The WGS has a long history of evolution, starting from the World War two, when the United States Department of Defence introduced WGS60. Along with the increase in the accuracy and satellite observations, developments in WGS lead to WGS66, WGS72 and subsequently superseded by WGS84 since January 1987. As GPS positions are referred to the WGS84 datum, in order to establish control points in surveying at least one location’s absolute co-ordinates need to be available in WGS84 datum as a reference station (Ghosh and Rao, 2001). However, all mapping in India is based on India Geodetic System (Everest Spheroid), which can differ from WGS84 by few meters to tens of meters at different places. Agarwal (2001) reported that the Indian datum is estimated to be nearly one Km away from C.G. of the earth, whereas WGS84 is only +2 meters away, which represents ideal geocentric world system. The above issue informs that GPS users in Indian and other countries need to consider datum transformation to achieve higher level of accuracy.

Considering this, Indian Ministry of Defence has realised that all maps in India should be transformed to WGS84 datum for data compatibility. When it is known that integration of geoinformation technologies in an enterprise model can yield higher benefits on the basis of compatibility and interoperability of data, consideration of issues such as data sharing, co-ordination, augmentation of resources and infrastructure carry vital importance for widespread diffusion of GPS. Furthermore, at present in the absence of second order GPS network in India, it is difficult and time consuming for users to establish their base station for DGPS. An estimate suggests that establishment of first and second order GPS network in India can take more than 5-6 years. According to Kulkarni (2002) the national committee for GPS in India, constituted under the Department of Space (DOS), has recommended establishment of a three-tier network of GPS stations- two Permanent Reference Stations (PRS), four Permanent Monitoring Stations (PMS) and a number of Mobile Monitoring Stations (MMS). The developments in this direction will open-up great potentiality of GPS applications, and also create India’s presence on the global scenario. Particularly at this stage, following developments can accelerate diffusion of GPS integrated services in India:

establishment of high precision zero order Geodetic National Survey Control Networks
densification and readjustment of existing Primary Control Networks,
densification of survey controls for topographic and cadastral surveys, and
densification of ground controls for photogrammetric survey and mapping.

The emerging trends
GPS applications in civil uses have started with breakthrough in surveying applications. Nevertheless, GPS integration in other spheres has come a long way in a short time, and very rapidly GPS solutions are becoming so embedded and hidden within daily life that users hardly knows that they are using GPS. By all indications, the increasing integration of geoinformation technologies and improving customisation will provide ground for profound applications for environmental specialists, GIS data collectors, navigators, geophysicists, leisure/recreational industry and civil, transportation, and utility engineers. Furthermore, improving accuracy of GPS using Carrier-Phase GPS and Real-Time-Kinematic is opening up doors for the use of GPS in many new areas.

The advent of small GPS has enhanced utility of GIS, GPS and PDA integrated mobile mapping solutions. The integrated solution using wireless modem has enabled two-way information exchange for fieldwork, aiding real-time decision-making. The space Application Centre, Ahmedabad has successfully piloted GIS-GPS integrated mobile platform for field data collection using Compaq iPAQ pocket PC with 12-channel GPS receiver and GSM modem for wireless connectivity (Udani and Goel, 2002). Furthermore, Satyaprakash (2002) reported that integration of lightweight GIS plug-in such as ArcPad from ESRI provides compatibility with other GIS tools and hyperlink with client-server offers real-time updating of field data. According to a survey of latest GPS products by Graham (2000), lightweight (nearly 0.635 Kg.) pocket receivers with GIS interface have sufficient rechargeable battery life to support full day of field mapping.

The innovative GPS applications, integrated with other geoinformation and ICTs will offer achievement of higher accuracy at reduced costs, with increased productivity and greater working flexibility. The availability of smaller, inexpensive and convenient GPS receivers has offered a mainstream integrated tool for surveying and mapping applications. GPS brings new opportunities by providing solutions to long-standing problems, which became less formidable by integration of GPS with other geoinformation and communication technologies. The inter- and interdisciplinary exchange of information/data offers the cutting edge `geoinformation’ revolution in surveying and field mapping.

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