Method for initiating navigation guidance in a distributed communications system

1. A method for navigation guidance in a distributed navigation guidance system comprising a portable navigation device having a first navigation operating mode for requesting and receiving routelet data and navigation route data and operating in accordance with the routelet data and a second navigation operating mode for operating in accordance with the navigation route data, the method comprising the steps of:

in the first navigation operating mode, transmitting a navigation route request comprising first location data and a destination location, the first location data determined in response to a present location of the portable navigation device when the navigation route request is transmitted and transmitting a routelet request comprising second location data, speed data and direction data, wherein the second location data and the speed and direction data are determined in response to a present location, a present speed and a present direction of travel, respectively, of the portable navigation device when the routelet request is transmitted;

receiving routelet data; and

operating in accordance with the received routelet data, wherein operating in accordance with the received routelet data includes switching operation of the portable navigation device from the first navigation operating mode to the second navigation operating mode in response to the received routelet data intersecting a main route, the main route defined by received navigation route data comprising routing data describing the main route from a route start location determined in response to the first location data to the destination location.

2. The method for navigation guidance in accordance with claim 1 wherein the distributed navigation guidance system further comprises a remote navigation guidance device, the method further comprising the steps of:

receiving the navigation route request at the remote navigation guidance device;

the remote navigation guidance device generating the navigation route data;

generating initial routelet data describing at least one routelet from the present location of the portable navigation device corresponding to the first location data to the main route; and

transmitting the navigation route data and the initial routelet data to the portable navigation device.

3. The method for navigation guidance in accordance with claim 1 wherein the step of switching operation of the portable navigation device comprises the steps of:

repeating the steps of transmitting a routelet request, receiving routelet data and operating in accordance with the received routelet data if the received routelet data is not applicable to the present location of the portable navigation device when the received routelet data is received; and

switching operation of the portable navigation device from the first navigation operating mode to the second navigation operating mode in response to the received routelet data intersecting the main route.

4. The method for navigation guidance in accordance with claim 1 wherein the step of switching operation of the portable navigation device comprises the steps of:

receiving navigation route data comprising routing data and received routelet data, the routing data describing the main route to navigate from the route start location to the destination location;

switching operation of the portable navigation device from the first navigation operating mode to the second navigation operating mode in response to the received routelet data intersecting the main route.

5. The method for navigation guidance in accordance with claim 1 wherein the step of switching operation of the portable navigation device comprises the steps of:

repeating the steps of transmitting a routelet request, receiving routelet data and operating in accordance with the received routelet data if the received routelet data is not applicable to the present location of the portable navigation device when the received routelet data is received or if the received routelet data does not intersect with the main route; and

switching operation of the portable navigation device from the first navigation operating mode to the second navigation operating mode in response to the received routelet data intersecting the main route.

6. A method for navigation guidance of a portable navigation device in a distributed navigation guidance system comprising a remote navigation guidance device and the portable navigation device, the portable navigation device having a first navigation operating mode for requesting and receiving routelet data and navigation route data and operating in accordance with the routelet data and a second navigation operating mode for operating in accordance with the navigation route data, the method for navigation guidance of the portable navigation device comprising the steps of:

the portable navigation device in the first navigation operating mode transmitting a routelet request comprising location data, speed data and direction data, wherein the location, speed and direction data is determined in response to a present location, a present speed and a present direction of travel, respectively, of the portable navigation device when the routelet request is transmitted;

the remote navigation guidance device receiving the routelet request transmitted by the portable navigation device;

the remote navigation guidance device generating routelet data in response to the location data, the speed data, the direction data and at least one primary travel road within a predetermined distance from the portable navigation device as indicated by the location data;

the remote navigation guidance device transmitting the routelet data to the portable navigation device;

receiving the routelet data at the portable navigation device; and

the portable navigation device operating in accordance with the received routelet data.

7. The method for navigation guidance in accordance with claim 6 wherein the step of the remote navigation guidance device generating the routelet data comprises the steps of:

the remote navigation guidance device determining a nearest road segment to the portable navigation device in response to the location data and predetermined road information;

the remote navigation guidance device determining whether the portable navigation device is located on road or located off road in response to the location data and the nearest road segment; and

the remote navigation guidance device generating the routelet data in response to whether the portable navigation device is located on road or located off road.

8. The method for navigation guidance in accordance with claim 7 wherein the step of the remote navigation guidance device determining whether the portable navigation device is located on road or located off road comprises the step of determining that the portable navigation device is located off road in response to the location data indicating that the portable navigation device is greater than or equal to a predetermined distance from the nearest road segment, and wherein the step of the remote navigation guidance device generating the routelet data comprises the steps of:

determining that the portable navigation device is stationary in response to the speed data indicating that the portable navigation device is traveling at a speed less than a predetermined speed; and

generating the routelet data for travel in a routelet area defined in response to the location data, the speed data and the direction data, the routelet data defined in response to the location data and the nearest road segment if the portable navigation device is located off road and the portable navigation device is stationary, and wherein the routelet data further comprises off road indication data if the portable navigation device is located off road and the portable navigation device is stationary.

9. The method for navigation guidance in accordance with claim 7 wherein the step of the remote navigation guidance device determining whether the portable navigation device is located on road or located off road comprises the step of determining that the portable navigation device is located off road in response to the location data indicating that the portable navigation device is greater than or equal to a predetermined distance from the nearest road segment, and wherein the step of the remote navigation guidance device generating the routelet data comprises the steps of:

determining that the portable navigation device is moving in response to the speed data indicating that the portable navigation device is traveling at a speed greater than a predetermined speed; and

generating the routelet data for travel in a routelet area defined in response to the speed data and the direction data, the routelet data defined in response to the location data, the nearest road segment and a main route if the portable navigation device is located off road and the portable navigation device is moving, wherein the main route defined in response to a route start location and a destination location.

10. The method for navigation guidance in accordance with claim 7 wherein the step of the remote navigation guidance device generating the routelet data further comprises the step of the remote navigation guidance device determining that the portable navigation device is stationary in response to the speed data indicating that the portable navigation device is traveling at a speed less than a predetermined speed, and wherein the step of the remote navigation guidance device generating the routelet data comprises the step of the remote navigation guidance device determining that the portable navigation device is located on road in response to the location data indicating that the portable navigation device is less than a predetermined distance from the nearest road segment, and wherein the step of the remote navigation guidance device determining whether the portable navigation device is located on road or located off road comprises the step of the remote navigation guidance device generating the routelet data for travel in a routelet area defined in response to the location data, the speed data and the direction data, wherein the routelet data is defined in response to the location data and a main route if the portable navigation device is located on road and the portable navigation device is stationary, and wherein the main route is defined in response to a route start location and a destination location.

11. The method for navigation guidance in accordance with claim 7 wherein the step of the remote navigation guidance device determining whether the portable navigation device is located on road or located off road comprises the step of determining that the portable navigation device is located on road in response to the location data indicating that the portable navigation device is less than a predetermined distance from the nearest road segment wherein the step of the remote navigation guidance device generating the routelet data comprises the steps of:

determining that the portable navigation device is moving in response to the speed data indicating that the portable navigation device is traveling at a speed greater than or equal to a predetermined speed; and

generating the routelet data for travel in a routelet area defined in response to the speed data and the direction data, the routelet data defined in response to the location data and a main route if the portable navigation device is located on road and the portable navigation device is moving, wherein the main route is defined in response to a route start location and a destination location.