Accelerometer
A device to measure the acceleration externally applied to
it.
[Section 5.4]
Almanac
An Almanac contains ephemeris data on all the satellites,
and a complete almanac is valid for thirty days, at which
time a new almanac must be downloaded from the satellites
for the upcoming month. The GPS receiver automatically
updates its internal almanac upon locking onto a GPS
satellite.
[Section 4.2.3]
Altitude
The current elevation from sea level that the GPS receiver
is located.
[Section 4.1.2.8]
ANS (Alternative Navigation System)
This was the system built to work in conjunction with
Strider to provide seamless position tracking of a
pedestrian.
[Section 1.4]
Atlas Speaks
Atlas Speaks is a Microsoft Windows-based program for a
personal computer that presents map data verbally through a
speech synthesizer.
[Section 1.1]
Azimuth
The number of degrees from north, that an object is
positioned. This is used in tracking where the satellites
are positioned in the sky.
[Section 4.1.2.9]
Cyclic Redundancy Check (CRC)
This is a byte added to the end of a data packet that is
used to verify the data preceding it is valid.
[Section6.3.4]
Datum
A datum is a network of monuments and reference points
defining a mathematical surface from which geographic
computations can be made.
[Section 4.3.1.1]
Dead Reckoning
A method of navigation based on a known starting position,
and tracking distance travelled and direction.
[Section 5.5]
Differential GPS (DGPS)
A system to precisely determine the location of the DGPS
receiver. This system uses a known stationary GPS receiver
to track the same GPS signals as those picked up by
adjacent receivers. Using FM radio transmissions, the
system transmits error corrections to those receivers.
[Section 1.4]
Dynamically Linked Library (DLL)
A Microsoft Windows-based program linked in at run-time.
Atlas Speaks and Strider has two such DLL's, one for
language (i.e. speech synthesis), and another for the GPS
specific receiver.
[Section 3.2.1]
ETAK Coverage Area Map (ECA)
This is the ETAK given name for a particular digital map
which Atlas Speaks and Strider uses. These ECA's are
non-overlapping geographic regions which are complete
counties or collections of complete counties.
[Section3.2.4.2]
Ephemeris
A mathematical model of where the satellites are positioned
in the sky.
[Section 5.1]
Geometric Dilution of Precision (GDOP)
A factor that modifies the error in the GPS position based
on satellite configuration and timing.
[Chapter 5]
Geographical Information System (GIS)
A database containing map data. In our case, this is a map
of a city with important features associated with it such
as house numbers, postal codes, types of roads etc.
[Section 1.4]
Global Positioning System (GPS)
A system designed by the United States Department of
Defense, using satellites to locate one's position on the
earth.
[Section 1.1]
Header
This is the first byte sent in a data packet, which the
computer uses to synchronize itself with the data coming
in.
[Section 6.3.4]
Interrupt Request (IRQ)
An IRQ is a request to service a particular hardware device
or update a specific section of the program. When an IRQ
occurs the appropriate ISR will be called to service the
request.
[Section 6.1.4]
Interrupt Service Routine (ISR)
An ISR is a section of code that will service a particular
interrupt request.
[Section 6.1.4.1]
Least Significant Bit (LSB)
The LSB is the right most bit in a binary number. For
Example 00000001, 1 is the LSB.
[Section 6.3.3.3]
Line-of-sight
In order for the GPS receiver to receive signals from the
satellites, it must have an unobstructed view to them.
Objects such as tall buildings and bridges can block the
line-of-sight needed by the receiver to obtain a position
solution.
[Chapter 5]
Multipath error
Errors caused by the interference of a signal that has
reached the receiver antenna by two or more different
paths. This is usually caused by one path being bounced or
reflected.
[Section 5.1.2]
Packet
A grouping of data sent through the RS-232 comm port . The
Packet length in this case is 20 bytes, consisting of a
header, 18 data bytes, and a CRC trailer byte.
[Section6.1.3]
Pedometer
A device used to count the number of steps a person takes.
[Section 1.4]
Points of Interest
"Points of Interest" are specific locations on a map such
as public buildings, monuments, parks, and landmarks.
[Section 2.1.3]
Position Dilution of Precision (PDOP)
A positioning of the satellites with respect to the GPS
receiver that modifies the error in the GPS position
solution.
[Section 4.1.2.1]
Position Solution
When the GPS receiver is tracking three or more satellites,
a location or position solution can usually be calculated.
This position solution is the location of the receiver.
[Section 4.1.2.2]
Request to Send (RTS)
The laptop's RS-232 port has a RTS that the computer will
lower when it wants the ANS to transmit its data over the
RS-232 link.
[Section 6.3.4]
Route
A Route is a path to a specific destination made up of a
number of waypoints.
[Section 2.1.3]
RS-232
RS-232 is a standard defined an asynchronous serial
communication method. Data is transferred to and from the
computer through a comm (communication) port that uses this
RS-232 method of communication.
[Section 6.1.3]
Serial Data Output (SDO)
This is the data pin of the Vector 2X digital compass. A
sixteen bit binary number representing a heading in degrees
is clocked-out through this pin.
[Section 6.3.3.1]
Selective Availability (S/A)
A policy adopted by the Department of Defense to introduce
some intentional clock noise into the GPS satellite signals
thereby degrading their accuracy for civilian users.
[Chapter 4]
Signal-to-Noise Ratio (SNR)
A measure of the quality of the signal strength the GPS
receiver receives from a satellite.
[Section 4.1.2.9]
Serendipity
Serendipity is a name given to the automatic presentation
of "Points of Interest" while traveling.
[Section 3.2.8]
Strider
Strider is the Atlas Speaks program with additional
hardware running on a laptop computer. It provides
position information and tracking using GPS and DGPS
receivers. This information is verbally spoken to the
pedestrian through synthesized speech.
[Section 1.1]
Universal Asynchronous Receiver-Transmitter (UART)
A UART is the programmed microchip that controls a
computer's interface to its comm port. It provides the
computer with the RS-232 interface so that it can "talk" to
and exchange data with other serial devices.
[Section 6.2]
Waypoint
A Route is made up from a number of waypoints, which break
up the route into smaller segments.
[Section 3.1.4.1]