HIPS - UCD : Localization and Orientation Capabilities of
GPS
HIPS Project Meeting
IRST, Trento, Italy
28 - 29 April 1998
G.M.P O’Hare, R. O’Rafferty, K. Sewell
Contents
• Garmin GPS II+ description
• Connecting Apple MessagePad with
Garmin GPS II+
• Field Trials with Garmin GPS II+
• Conclusions and Recommendations
Garmin GPS II+ Specification (1)
• 12 Parallel Channel Receiver
– Can track up 12 GPS satellites at once
• Accuracy
– 1-5 m with DGPS
– Only 100m is guaranteed due to SA
• Physical Specification
– Size : 5.86 x 12.7 x 4.11 cm
– Weight : 255 g
Garmin GPS II+ Specification (2)
• Initial Position Acquisition Time
– 15sec (Warm start)
– 45sec (Cold Start)
– Position is updated every 1 second
• Interfaces
– NMEA 0183 protocol is output over RS-232
Garmin GPS II+ Specification (3)
• Navigation Features
– GPS II+ can store the following
• 500 waypoints (an individual Latitude/Longitude
reading)
• 20 Routes containing 30 waypoints each
– These pieces of data can be uploaded to a
PC/Mac using Garmins GRMN/GRMN
protocol
Connecting Apple MessagePad with Garmin GPS
II+ (1)
• Physical Connection
– Garmin Serial cable connecting data output port
of the GPS II+ to the Serial port of the Apple
MessagePad (RS-232 connection)
• GPS II+ Data Output
– The GPS II+ outputs data complying with the
NMEA (National Marine Electronics
Association) 0183 standard at 4800 baud
Connecting Apple MessagePad with Garmin GPS
II+ (2)
• Sample NMEA 0183 Sentence
– $GPGLL,53.18.595,N, 006.13.400,W
– GPGLL : Indicates that the data was generated
by a GPS device (lat/long)
– 53 degrees, 18’,595” North
– 6 degrees,13’,400” West
– Sentence is terminated with Carriage Return,
Line Feed
Connecting Apple MessagePad with Garmin GPS
II+ (3)
• Software Interface
– Written in NewtonScript using the Newton
Communications API, the “Endpoint”
– Data bits, Stop bits and bps options are set to
Interoperate with the GPS device
Connecting Apple MessagePad with Garmin GPS
II+ (4)
PROCEDURE MakeConnection()
Begin
EndPoint:Instantiate(Endpoint Options);
EndPoint:Bind(Serial Port); // Bind code to Serial Port
EndPoint:Listen(); // Wait for Input
EndPoint:Accept();
EndPoint:ProcessInput(); // Parse the NMEA data
EndPoint:Disconnect();
End
The IMP TourGuide
• Field trials were carried out using an IMP
(Intelligent, Mobile, Personalised Systems)
demonstrator, which is a handheld
tourguide for the UCD campus
• The IMP TourGuide provides two modes of
operation
– Static Tour
– Dynamic Tour
The IMP TourGuide (2)
• Static Tour
– User makes initial
exploration of location
by interacting with a
map displayed on the
MessagePad
– When a location on the
map is clicked,
relevant information is
presented to the user
The IMP TourGuide (3)
• Dynamic Tour
– The dynamic tour
provides tour
information while the
user is physically
exploring the UCD
campus
– This mode is pro-active
and does not require
user interaction to
function
The IMP TourGuide (4)
• Dynamic Tour
– Positional information
is captured from the
GPS device
– Location relevant
information is retrieved
using the position data
(lat/long) as the lookup
key
The IMP TourGuide (5)
The IMP TourGuide (6)
• While the user is taking the tour, it is possible to
build up a route and store this information along
with the users profile
• The Garmin GPS II+ currently allows the user to
upload waypoints and route to a PC / Mac after
usage (effectively offline)
• Another option is to store the positional data on
the palmtop, such that the route is stored when the
tour is finished and can be automatically uploaded
to the database
The IMP TourGuide (7)
PROCEDURE StorePos(Lat,Long)
BEGIN
// Store Current Position in Route
route[next].lat := Lat;
route[next].long := Long;
route.next := route.next + 1;
END
Field Trials
• Field trials were carried out using the IMP
TourGuide
• Experiments focused on the following:
– Position Lock
– Affects of building coverage
– Accuracy
– Orientation
Field Trials - Localization (1)
• Position Lock
– A GPS signal cannot be received indoors
– Require a minimum of 3 GPS signals (2-D)
– 3-D Navigation (lat/long/alt) requires at least 4
GPS signals
– Initial usage requires 15-45s the find position
• Building Coverage
– Tall buildings can affect the GPS signal if the
user is less than ~5m from the building
Field Trials - Localization (2)
• Building Coverage
– may lose one GPS signal
– Altitude parameter may be lost (3D -> 2D)
• Accuracy
– Given the situation with Selective Availability
(SA), Accuracy can be off by up to 100m
– Trials with the GPS II+ set accuracy at ~15m
Field Trials - Localization (3)
• Accuracy - DGPS Add-on
– An accuracy of 1-5m can be attained with a
Differential GPS (DGPS) beacon
– DGPS is removes SA error with a different
thirds party signal
– DGPS costs twice the price as a GPS receiver
– DGPS requires a 1-2m antenna
Field Trials - Orientation
• GPS devices do not have Compass a
capability
• Heading can be calculated given 2 positions
• Heading, in general is only useful for in-car
usage, or user with definite current heading
• Without a current and constant heading
Orientation is inaccurate
Conclusions and Recommendations
• Outdoor Localization is possible with an
accuracy of ~15m
• Signal maybe lost for short periods in areas
of heavy building coverage
• A PCMCIA GPS maybe more appropriate
as the GPS II+ is bulky
Conclusions and Recommendations
• With an on-foot tourist in mind, orientation
is not reliable from a GPS device.
• Electronic compasses maybe an option
– Precision Navigation Inc