You are using an outdated browser that does not fully support the intranda viewer.
As a result, some pages may not be displayed correctly.

We recommend you use one of the following browsers:

Full text

The 3rd ISPRS Workshop on Dynamic and Multi-Dimensional GIS & the 10th Annual Conference of CPGIS on Geoinformatics
Chen, Jun

ISPRS, Vol.34, Part 2W2, “Dynamic and Multi-Dimensional GIS”, Bangkok, May 23-25, 2001
Ying. GAO and Zhi. LIU
Department of Geomatics Engineering
The University of Calgary
2500 University Drive N.W.
Calgary, Alberta, Canada T2N 1N4
Tel: 403-220-6174 Fax: 403-284-1980
Email: gao@geomatics.ucalgary.ca
KEYWORDS: GPS, Wireless, Internet, Differential Positioning
A differential GPS positioning system is able to provide more precise position solutions than a stand-alone system through the
application of corrections calculated at a reference station or a network of reference stations with known surveyed coordinates.
Differential corrections are usually transmitted to the users via radio, beacon or communication satellite. In this paper, the concept of
differential GPS positioning based on wireless Internet has been be described. To assess the feasibility of the proposed method, a
prototype system has been developed and tested in the field using CDPD-based wireless Internet access. The field results have shown
satisfactory positioning accuracy and differential data latency over the Internet. In addition to Internet advantages for wireless
communication, the use of the Internet to develop new positioning methods has also been discussed.
Measurements made from Global Positioning System (GPS) are
affected by a number of error sources including satellite orbit
error, satellite clock error and atmospheric effects. Autonomous
GPS positioning is therefore subject to the effects of all the
above error sources and can provide positioning accuracy only
in the neighborhood of about 10 meters. Therefore, in order to
achieve higher positioning accuracy such as in the order of
meter to centimeter level, differential GPS (DGPS) techniques
must be employed.
The objective for DGPS is to reduce the error sources within the
GPS satellite clock and orbit data, atmosphere effects as well as
other errors due to GPS receivers. Using DGPS method, at
least two GPS receivers must be used with one serving as a
reference receiver station with precise known coordinates, and
the other as the rover station for which positioning is required.
The reference station is used to generate differential corrections
be applied by the rover station to reduce the above mentioned
error sources and subsequently to derive an improved position
solution. Due to the use of a reference station, the method is
effective only for short reference-rover separations because the
spatial correlation of the error sources between the reference
and rover stations reduces as the increase of the reference-
rover separation. DGPS positioning using a single reference
station is often referred as Local Area DGPS (LADGPS).
To increase the effective area of the generated differential
corrections, multiple reference receiver stations are often
employed to form a reference network. Dependent on the size of
the network, there are two different types of reference networks,
a) Wide Area DGPS (WADGPS) network and
b) Regional Area DGPS (RADGPS) network.
A WADGPS network focus on providing differential correction
service continental-wide even worldwide while a RADGPS
network focus on a region of hundred kilometers in dimension
(Gao et al., 1997). A number of different WADGPS and
RADGPS networks have been implemented to date and many
others are currently under development. The US Wide Area
Augmentation System (WAAS) is a typical example of
WADGPS networks whose reference station separations are
typically a few thousand kilometers apart (Loh, 1995). WAAS
differential corrections are currently available with obtainable
position accuracy at the meter-level although the network is not
yet fully operational. On the other hand, a RADGPS network
consist of multiple reference stations separated in the range of
several hundred kilometers and the Swedish SWEPOS network
is a typical example of such networks (Hedling, et al., 1996).
For real-time applications, no matter what type of DGPS
systems you may implement, a continuous data link must be
established between the reference network and the remote
users in order for the DGPS users to receive the network
generated differential corrections. For local and regional area
differential positioning, radios and local communication systems
are typically used while for wide area differential positioning
satellite communication is appropriate although it is much more
expensive to use. As the advance of Internet technology and its
fast expansion of the coverage and mobile accessibility, it has
been widely demonstrated that the Internet could become a
cost-effective and efficient alternative for a wide range of
applications including differential positioning that we will discuss
in this paper.
This paper describes recent research results in the use of
Internet as the communication link for differential positioning
and navigation applications. The paper will show that Internet-
based differential positioning systems are advantageous when
compared to current DGPS systems. The technology will not
only improve the efficiency of implementing DGPS technologies
but also potentially expand significantly the application spectrum
of DGPS technology with new differential positioning methods.
The paper is organized as follows. The paper will first provide a
brief description of the Internet and its characteristics as a
communication tool. Differential satellite positioning using
Internet and a prototype system are then described followed
with the introduction of a new Internet-based mobile-to-mobile
solution to multiple moving platform applications. Field test
results are finally provided to assess the obtainable differential
positioning accuracy of an Internet-based system and its
feasibility to be used in operational environments.
Internet is characterized by its low cost, easy accessibility,
availability, flexibility, and expandability. Currently the expense