Navigation System: Description and Operation
System Description
OUTLINE
The Navigation System (Multi-AV System) relies upon three sensing devices in order to determine vehicle location at regular time intervals.
1. Vehicle speed sensor: Determines the distance the vehicle has traveled.
2. Gyro (Angular velocity sensor): Determines vehicle steering angle and directional change.
3. GPS antenna (GPS data): Determines vehicle forward movement and direction.
The data provided by the three sensing functions together with a comparison of the mapping information read from the CD-ROM drive permit accurate determination of the vehicle's current location and subsequent course (map matching). The information appears on a liquid crystal display.
This comparison of GPS data (vehicle position sensing) and map matching permits precise determination of vehicle location.
Position Sensor Operating Principles
The sensor determines current vehicle location by calculating the previously sensed position the distance traveled from this position and the directional changes occurring during this travel.
1. Distance traveled
The distance traveled is calculated using signals received from the vehicle speed sensor. The sensor automatically compensates for the slightly reduced wheel and tire diameter resulting from tire wear.
2. Forward movement (Direction)
Changes in the direction of forward movement are calculated by the gyro (angular velocity sensor) and the GPS antenna (GPS data). Each of these functions has its advantage and disadvantages. Depending upon conditions one function takes precedence over the other to accurately determine the direction of forward movement.
Map Matching
Map matching allows the driver to compare the sensed vehicle location data with the road map contained in the CD-ROM drive. Vehicle position is marked on the CD-ROM map. This permits the driver to accurately determine his/her present position on the highway and to make appropriate course decisions.
When GPS data reception is poor during travel the vehicle position is not amended. At this time manual manipulation of the CDROM map position marker is required.
Map matching permits the driver to make priority judgments about possible appropriate roads other than the one currently being traveled.
If there is an error in the distance or direction of travel there will also be an error in the relative position of other routes. When two routes are closely parallel to one another the indicated position for both routes will be nearly the same priority. This is so that slight changes in the steering direction may cause the marker to indicate both routes alternately.
Newly constructed roads may not appear on the CD-ROM map. In this case map matching is not possible. Changes in the course of a road will also prevent accurate map matching.
When driving on a road not shown on the CD-ROM map the position marker used for map matching may indicate a different route. Even after returning to a route shown on the map the position marker may jump to the position currently detected.
GPS (Global Positioning System)
GPS is the global positioning system developed and operated by the US Department of Defense. GPS satellites (NAVSTAR) transmit radio waves and orbit around the earth at an altitude of approximately 21,000 km (13,000 miles).
GPS receiver calculates the three-dimensional position of the vehicle (latitude longitude and altitude from the sea level) by the time difference of the radio wave arriving from more than four GPS satellites (three-dimensional positioning).
When the radio wave is received from only three GPS satellites the two-dimensional position (latitude and longitude) is calculated using the altitude from the sea level data calculated by using four GPS satellites (two-dimensional positioning).
Positioning capability is degraded in the following cases.
- In two-dimensional positioning when the vehicle's altitude from the sea level changes the precision becomes lower.
- The location detection performance can have an error of about 100 m (300 ft) even in three-dimensional positioning with high precision. Because the precision is influenced by the location of GPS satellites used for positioning the location detection performance may drop depending on the location of GPS satellites.
- When the radio wave from GPS satellites cannot be received for example when the vehicle is in a tunnel in a parking lot inside building under an elevated superhighway or near strong power lines the location may not be detected. Turbulent/electric weather conditions may also affect positioning performance. If something is placed on the antenna the radio wave from GPS satellites may not be received.
COMPONENT DESCRIPTION
Display & NAVI Control Unit
- The gyro (angular speed sensor) and the CD-ROM drive are built-in units that control the navigation functions.
- Signals are received from the gyro the vehicle speed sensor and the GPS antenna. Vehicle location is determined by combining this data with the data contained in the CD-ROM map. Locational information is shown on liquid crystal display panel.
- Finger-operated touch switches are positioned on the liquid crystal display panel for easy operation.
- The touch switches used to control the equipment are beneath a glass sheet and two resistance membranes at the top of the liquid crystal display panel. The switches are sensitive to resistance value where touched with your finger to detect operating status.
CD-ROM Driver
Maps traffic control regulations and other pertinent information can be easily red from the CD-ROM disc.
NOTE:
- When removing the CD-ROM allow it to remain open until the liquid crystal display locks.
- The liquid crystal display must be closed when the vehicle is running.
- Do not place cups cans or other containers containing liquids on top of the liquid crystal display.
Map CD-ROM
- The map CD-ROM has maps traffic control and other pertinent information.
- To improve CD-ROM map matching and route determination functions the CD-ROM uses an exclusive Nissan format. Therefore the use of a CD-ROM provided by other manufacturers cannot be used.
Gyro (Angular Speed Sensor)
- The oscillator gyro sensor is used to detect changes in vehicle steering angle.
- The oscillator gyro periodically senses oscillatory variation at the oscillation terminals. This variation is caused by changes in the vehicle angular velocity. Voltage variations are sensed by ceramic voltage sensors at the left and right sides of the terminals. Vehicle angular velocity corresponds directly with these changes in voltage.
- The gyro is built into the display & navigation (NAVI) control unit.
BIRDVIEW(R)
The BIRDVIEW(R) provides a detailed and easily seen display of road conditions covering the vehicle's immediate to distant area.
Description
- Display area: Trapezoidal representation showing approximate distances (Wn, D and Wd).
- Ten horizontal grid lines indicate display width while six vertical grid lines indicate display depth and direction.
- Drawing line area shows open space depth and immediate front area. Each area is to a scale of approximately 5:6:25.
- When the "ZM-" button is pushed the view point height is increased. Pushing the "ZM+" button decreases the height.
Pushing the "ZM-" button or the "ZM+" button during operation indicates the scale change and the view point height at the left-hand side of the screen.
FUNCTION OF TOUCH SWITCH (SUMMARY)
Display with Pushed "MAP" Switch
The function of each touch switch is as follows:
1. Azimuth indication
2. Position marker
The tip of the arrow shows the current position. The shaft of the arrow indicates the direction in which the vehicle is traveling.
3. GPS reception signal (indicates current reception conditions)
4. Distance display (shows the distance in a reduced scale)
5. Current location voice information (this information is available when the route guide is being activated and the designated route is being traveled.)
6. Switch display from map screen to BIRDVIEW(R) screen (change to map screen on display when the BIRDVIEW(R) is being used.)
7. The following items can be set.
- Save Current Location
- Edit Address Book
- Guide Volume
- System Setting
8. The route guide operation can be canceled.
Display with Pushed "DEST" Switch
Display with Toutch Screen