|
The cutting edge 'Geoinformation' revolution
- 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.
|
|
