WO2009132682A1

WO2009132682A1 - Navigation device & method

Info

Publication number: WO2009132682A1
Application number: PCT/EP2008/003712
Authority: WO
Inventors: Wojciech Mlynarczyk
Original assignee: TomTom International BV
Current assignee: TomTom International BV
Priority date: 2008-05-02
Filing date: 2008-05-02
Publication date: 2009-11-05
Anticipated expiration: 2010-11-02
Also published as: TW200946869A

Abstract

This invention relates to a navigation device (500) comprising a processor (510) and an accelerometer (500) arranged to output measured acceleration information to the processor (510), wherein the processor (510) is arranged to correct the measured acceleration information for an effect of gravity by utilising pitch angle information.

Description

NAVIGATION DEVICE & METHOD

Field of the Invention

This invention relates to navigation devices and to methods for determining a current location. Illustrative embodiments of the invention relate to portable navigation devices (so-called PNDs), in particular PNDs that include Global Positioning System (GPS) signal reception and processing functionality. Other embodiments relate, more generally, to any type of processing device that is configured to execute navigation software so as to provide route planning, and preferably also navigation, functionality.

Background to the Invention

Portable navigation devices (PNDs) that include GPS (Global Positioning

System) signal reception and processing functionality are well known and are widely employed as in-car or other vehicle navigation systems.

In general terms, a modern PNDs comprises a processor, memory (at least one of volatile and non-volatile, and commonly both), and map data stored within said memory. The processor and memory cooperate to provide an execution environment in which a software operating system may be established, and additionally it is commonplace for one or more additional software programs to be provided to enable the functionality of the PND to be controlled, and to provide various other functions.

Typically these devices further comprise one or more input interfaces that allow a user to interact with and control the device, and one or more output interfaces by means of which information may be relayed to the user. Illustrative examples of output interfaces include a visual display and a speaker for audible output. Illustrative examples of input interfaces include one or more physical buttons to control on/off operation or other features of the device (which buttons need not necessarily be on the device itself but could be on a steering wheel if the device is built into a vehicle), and a microphone for detecting user speech. In a particularly preferred arrangement the output interface display may be configured as a touch sensitive display (by means of a touch sensitive overlay or otherwise) to additionally provide an input interface by means of which a user can operate the device by touch.

Devices of this type will also often include one or more physical connector interfaces by means of which power and optionally data signals can be transmitted to and received from the device, and optionally one or more wireless transmitters/receivers to allow communication over cellular telecommunications and other signal and data networks, for example Wi-Fi, Wi-Max GSM and the like.

PND devices of this type also include a GPS antenna by means of which satellite-broadcast signals, including location data, can be received and subsequently processed to determine a current location of the device.

The PND device may also include electronic gyroscopes and accelerometers which produce signals that can be processed to determine the current angular and linear acceleration, and in turn, and in conjunction with location information derived from the GPS signal, velocity and relative displacement of the device and thus the vehicle in which it is mounted. Typically such features are most commonly provided in in-vehicle navigation systems, but may also be provided in PND devices if it is expedient to do so.

The utility of such PNDs is manifested primarily in their ability to determine a route between a first location (typically a start or current location) and a second location (typically a destination). These locations can be input by a user of the device, by any of a wide variety of different methods, for example by postcode, street name and house number, previously stored "well known" destinations (such as famous locations, municipal locations (such as sports grounds or swimming baths) or other points of interest), and favourite or recently visited destinations.

Typically, the PND is enabled by software for computing a "best" or "optimum" route between the start and destination address locations from the map data. A "best" or

"optimum" route is determined on the basis of predetermined criteria and need not necessarily be the fastest or shortest route. The selection of the route along which to guide the driver can be very sophisticated, and the selected route may take into account existing, predicted and dynamically and/or wirelessly received traffic and road information, historical information about road speeds, and the driver's own preferences for the factors determining road choice (for example the driver may specify that the route should not include motorways or toll roads).

In addition, the device may continually monitor road and traffic conditions, and offer to or choose to change the route over which the remainder of the journey is to be made due to changed conditions. Real time traffic monitoring systems, based on various technologies (e.g. mobile phone data exchanges, fixed cameras, GPS fleet tracking) are being used to identify traffic delays and to feed the information into notification systems.

PNDs of this type may typically be mounted on the dashboard or windscreen of a vehicle, but may also be formed as part of an on-board computer of the vehicle radio or indeed as part of the control system of the vehicle itself. The navigation device may also be part of a hand-held system, such as a PDA (Portable Digital Assistant) a media player, a mobile phone or the like, and in these cases, the normal functionality of the hand-held system is extended by means of the installation of software on the device to perform both route calculation and navigation along a calculated route.

Route planning and navigation functionality may also be provided by a desktop or mobile computing resource running appropriate software. For example, the Royal Automobile Club (RAC) provides an on-line route planning and navigation facility at http://www.rac.co.uk, which facility allows a user to enter a start point and a destination whereupon the server to which the user's PC is connected calculates a route (aspects of which may be user specified), generates a map, and generates a set of exhaustive navigation instructions for guiding the user from the selected start point to the selected destination. The facility also provides for pseudo three-dimensional rendering of a calculated route, and route preview functionality which simulates a user travelling along the route and thereby provides the user with a preview of the calculated route.

In the context of a PND, once a route has been calculated, the user interacts with the navigation device to select the desired calculated route, optionally from a list of proposed routes. Optionally, the user may intervene in, or guide the route selection process, for example by specifying that certain routes, roads, locations or criteria are to be avoided or are mandatory for a particular journey. The route calculation aspect of the PND forms one primary function, and navigation along such a route is another primary function.

During navigation along a calculated route, it is usual for such PNDs to provide visual and/or audible instructions to guide the user along a chosen route to the end of that route, i.e. the desired destination. It is also usual for PNDs to display map information on-screen during the navigation, such information regularly being updated on-screen so that the map information displayed is representative of the current location of the device, and thus of the user or user's vehicle if the device is being used for in- vehicle navigation.

An icon displayed on-screen typically denotes the current device location, and is centred with the map information of current and surrounding roads in the vicinity of the current device location and other map features also being displayed. Additionally, navigation information may be displayed, optionally in a status bar above, below or to one side of the displayed map information, examples of navigation information include a distance to the next deviation from the current road required to be taken by the user, the nature of that deviation possibly being represented by a further icon suggestive of the particular type of deviation, for example a left or right turn. The navigation function also determines the content, duration and timing of audible instructions by means of which the user can be guided along the route. As can be appreciated a simple instruction such as "turn left in 100 m" requires significant processing and analysis. As previously mentioned, user interaction with the device may be by a touch screen, or additionally or alternately by steering column mounted remote control, by voice activation or by any other suitable method.

A further important function provided by the device is automatic route recalculation in the event that: a user deviates from the previously calculated route during navigation (either by accident or intentionally); real-time traffic conditions dictate that an alternative route would be more expedient and the device is suitably enabled to recognize such conditions automatically, or if a user actively causes the device to perform route re-calculation for any reason.

It is also known to allow a route to be calculated with user defined criteria; for example, the user may prefer a scenic route to be calculated by the device, or may wish to avoid any roads on which traffic congestion is likely, expected or currently prevailing. The device software would then calculate various routes and weigh more favourably those that include along their route the highest number of points of interest (known as POIs) tagged as being for example of scenic beauty, or, using stored information indicative of prevailing traffic conditions on particular roads, order the calculated routes in terms of a level of likely congestion or delay on account thereof. Other POI-based and traffic information-based route calculation and navigation criteria are also possible.

Although the route calculation and navigation functions are fundamental to the overall utility of PNDs, it is possible to use the device purely for information display, or "free-driving", in which only map information relevant to the current device location is displayed, and in which no route has been calculated and no navigation is currently being performed by the device. Such a mode of operation is often applicable when the user already knows the route along which it is desired to travel and does not require navigation assistance.

Devices of the type described above, for example the 720T model manufactured and supplied by TomTom International B. V., provide a reliable means for enabling users to navigate from one position to another.

A problem arises in that, during use, a GPS signal received by a navigation device may be lost. That is, a navigation device may not continually receive a GPS signal of sufficient strength, or from enough satellites, to enable a current location to be accurately determined. For example, a portable navigation device mounted in a car may not, for a period of time, receive a GPS signal of sufficient strength to calculate the car's current location when travelling through a built-up area or through a tunnel. However, it is desirable for the navigation device to continue providing route guidance to a user even when the GPS signal is lost for a period of time.

It is an aim of the present invention to address this problem, in particular to improve determination of a current location when a GPS signal is lost for a period of time.

Summary of the Invention

The present invention improves acceleration measurement by utilising information about a gradient or incline experienced by a navigation device. Reducing an error associated with measured acceleration allows a speed of movement of a navigation device to be calculated with a reduced error and, consequently, improves an accuracy of a current location calculated by dead reckoning.

In pursuit of this aim, a presently preferred embodiment of the present invention provides a navigation device comprising a processor and an accelerometer arranged to output measured acceleration information to the processor, wherein the processor is arranged to correct the measured acceleration information for an effect of gravity by utilising pitch angle information.

Another embodiment of the present invention relates to a method for use in a navigation device comprising measuring an acceleration of a navigation device, correcting the measured acceleration for an effect of gravity by utilising pitch angle information, determining a velocity of the navigation device, and updating a current location using the determined velocity.

Yet another embodiment of the present invention relates to computer software comprising one or more software modules operable, when executed in an execution environment, to cause a processor to: measuring an acceleration of a navigation device, correcting the measured acceleration for an effect of gravity by utilising pitch angle information, determining a velocity of the navigation device, updating a current location using the determined velocity.

Advantages of these embodiments are set out hereafter, and further details and features of each of these embodiments are defined in the accompanying dependent claims and elsewhere in the following detailed description.

Brief Description of the Drawings

Various aspects of the teachings of the present invention, and arrangements embodying those teachings, will hereafter be described by way of illustrative example with reference to the accompanying drawings, in which:

Fig. 1 is a schematic illustration of a Global Positioning System (GPS);

Fig. 2 is a schematic illustration of electronic components arranged to provide a navigation device;

Fig. 3 is a schematic illustration of the manner in which a navigation device may receive information over a wireless communication channel;

Figs. 4A and 4B are illustrative perspective views of a navigation device;

Fig. 5 is a block diagram of a system according to an embodiment of the present invention;

Fig. 6 is a flowchart depicting a method according to an embodiment of the present invention;

Fig. 7 is a further flowchart depicting a further method according to an embodiment of the present invention; and

Fig. 8 is a still further flowchart depicting a still further method according to an embodiment of the present invention.

Detailed Description of Preferred Embodiments

Preferred embodiments of the present invention will now be described with particular reference to a PND. It should be remembered, however, that the teachings of the present invention are not limited to PNDs but are instead universally applicable to any type of processing device that is configured to execute navigation software so as to provide route planning and navigation functionality. It follows therefore that in the context of the present application, a navigation device is intended to include (without limitation) any type of route planning and navigation device, irrespective of whether that device is embodied as a PND, a navigation device built into a vehicle, or indeed a computing resource (such as a desktop or portable personal computer (PC), mobile telephone or portable digital assistant (PDA)) executing route planning and navigation software.

It will also be apparent from the following that the teachings of the present invention even have utility in circumstances where a user is not seeking instructions on how to navigate from one point to another, but merely wishes to be provided information about a current location and, optionally, information about speed and/or direction of travel.

With the above provisos in mind, Fig. 1 illustrates an example view of Global Positioning System (GPS), usable by navigation devices. Such systems are known and are used for a variety of purposes. In general, GPS is a satellite-radio based navigation system capable of determining continuous position, velocity, time, and in some instances direction information for an unlimited number of users. Formerly known as NAVSTAR, the GPS incorporates a plurality of satellites which orbit the earth in extremely precise orbits. Based on these precise orbits, GPS satellites can relay their location to any number of receiving units.

The GPS system is implemented when a device, specially equipped to receive GPS data, begins scanning radio frequencies for GPS satellite signals. Upon receiving a radio signal from a GPS satellite, the device determines the precise location of that satellite via one of a plurality of different conventional methods. The device will continue scanning, in most instances, for signals until it has acquired at least three different satellite signals (noting that position is not normally, but can be determined, with only two signals using other triangulation techniques). Implementing geometric triangulation, the receiver utilizes the three known positions to determine its own two-dimensional position relative to the satellites. This can be done in a known manner. Additionally, acquiring a fourth satellite signal will allow the receiving device to calculate its three dimensional position by the same geometrical calculation in a known manner. The position and velocity data can be updated in real time on a continuous basis by an unlimited number of users.

As shown in Figure 1 , the GPS system is denoted generally by reference numeral 100. A plurality of satellites 120 are in orbit about the earth 124. The orbit of each satellite 120 is not necessarily synchronous with the orbits of other satellites 120 and, in fact, is likely asynchronous. A GPS receiver 140 is shown receiving spread spectrum GPS satellite signals 160 from the various satellites 120.

The spread spectrum signals 160, continuously transmitted from each satellite

120, utilize a highly accurate frequency standard accomplished with an extremely accurate atomic clock. Each satellite 120, as part of its data signal transmission 160, transmits a data stream indicative of that particular satellite 120. It is appreciated by those skilled in the relevant art that the GPS receiver device 140 generally acquires spread spectrum GPS satellite signals 160 from at least three satellites 120 for the GPS receiver device 140 to calculate its two-dimensional position by triangulation. Acquisition of an additional signal, resulting in signals 160 from a total of four satellites 120, permits the GPS receiver device 140 to calculate its three-dimensional position in a known manner.

Figure 2 is an illustrative representation of electronic components of a navigation device 200 according to a preferred embodiment of the present invention, in block component format. It should be noted that the block diagram of the navigation device 200 is not inclusive of all components of the navigation device, but is only representative of many example components.

The navigation device 200 is located within a housing (not shown). The housing includes a processor 210 connected to an input device 220 and a display screen 240. The input device 220 can include a keyboard device, voice input device, touch panel and/or any other known input device utilised to input information; and the display screen 240 can include any type of display screen such as an LCD display, for example. In a particularly preferred arrangement the input device 220 and display screen 240 are integrated into an integrated input and display device, including a touchpad or touch-screen input so that a user need only touch a portion of the display screen 240 to select one of a plurality of display choices or to activate one of a plurality of virtual buttons.

The navigation device may include an output device 260, for example an audible output device (e.g. a loudspeaker). As output device 260 can produce audible information for a user of the navigation device 200, it is should equally be understood that input device 240 can include a microphone and software for receiving input voice commands as well. In the navigation device 200, processor 210 is operatively connected to and set to receive input information from input device 220 via a connection 225, and operatively connected to at least one of display screen 240 and output device 260, via output connections 245, to output information thereto. Further, the processor 210 is operatively connected to memory 230 via connection 235 and is further adapted to receive/send information from/to input/output (I/O) ports 270 via connection 275, wherein the I/O port 270 is connectible to an I/O device 280 external to the navigation device 200. The external I/O device 280 may include, but is not limited to an external listening device such as an earpiece for example. The connection to I/O device 280 can further be a wired or wireless connection to any other external device such as a car stereo unit for hands-free operation and/or for voice activated operation for example, for connection to an ear piece or head phones, and/or for connection to a mobile phone for example, wherein the mobile phone connection may be used to establish a data connection between the navigation device 200 and the internet or any other network for example, and/or to establish a connection to a server via the internet or some other network for example.

Fig. 2 further illustrates an operative connection between the processor 210 and an antenna/receiver 250 via connection 255, wherein the antenna/receiver 250 can be a GPS antenna/receiver for example. It will be understood that the antenna and receiver designated by reference numeral 250 are combined schematically for illustration, but that the antenna and receiver may be separately located components, and that the antenna may be a GPS patch antenna or helical antenna for example.

Further, it will be understood by one of ordinary skill in the art that the electronic components shown in Fig. 2 are powered by power sources (not shown) in a conventional manner. As will be understood by one of ordinary skill in the art, different configurations of the components shown in Fig. 2 are considered to be within the scope of the present application. For example, the components shown in Fig. 2 may be in communication with one another via wired and/or wireless connections and the like. Thus, the scope of the navigation device 200 of the present application includes a portable or handheld navigation device 200.

In addition, the portable or handheld navigation device 200 of Fig. 2 can be connected or "docked" in a known manner to a vehicle such as a bicycle, a motorbike, a car or a boat for example. Such a navigation device 200 is then removable from the docked location for portable or handheld navigation use. Referring now to Fig. 3, the navigation device 200 may establish a "mobile" or telecommunications network connection with a server 302 via a mobile device (not shown) (such as a mobile phone, PDA, and/or any device with mobile phone technology) establishing a digital connection (such as a digital connection via known Bluetooth technology for example). Thereafter, through its network service provider, the mobile device can establish a network connection (through the internet for example) with a server 302. As such, a "mobile" network connection is established between the navigation device 200 (which can be, and often times is mobile as it travels alone and/or in a vehicle) and the server 302 to provide a "real-time" or at least very "up to date" gateway for information.

The establishing of the network connection between the mobile device (via a service provider) and another device such as the server 302, using an internet (such as the World Wide Web) for example, can be done in a known manner. This can include use of TCP/IP layered protocol for example. The mobile device can utilize any number of communication standards such as CDMA, GSM, WAN, etc.

As such, an internet connection may be utilised which is achieved via data connection, via a mobile phone or mobile phone technology within the navigation device 200 for example. For this connection, an internet connection between the server 302 and the navigation device 200 is established. This can be done, for example, through a mobile phone or other mobile device and a GPRS (General Packet Radio Service)- connection (GPRS connection is a high-speed data connection for mobile devices provided by telecom operators; GPRS is a method to connect to the internet).

The navigation device 200 can further complete a data connection with the mobile device, and eventually with the internet and server 302, via existing Bluetooth technology for example, in a known manner, wherein the data protocol can utilize any number of standards, such as the GSRM, the Data Protocol Standard for the GSM standard, for example.

The navigation device 200 may include its own mobile phone technology within the navigation device 200 itself (including an antenna for example, or optionally using the internal antenna of the navigation device 200). The mobile phone technology within the navigation device 200 can include internal components as specified above, and/or can include an insertable card (e.g. Subscriber Identity Module or SIM card), complete with necessary mobile phone technology and/or an antenna for example. As such, mobile phone technology within the navigation device 200 can similarly establish a network connection between the navigation device 200 and the server 302, via the internet for example, in a manner similar to that of any mobile device.

For GRPS phone settings, a Bluetooth enabled navigation device may be used to correctly work with the ever changing spectrum of mobile phone models, manufacturers, etc., model/manufacturer specific settings may be stored on the navigation device 200 for example. The data stored for this information can be updated.

In Fig. 3 the navigation device 200 is depicted as being in communication with the server 302 via a generic communications channel 318 that can be implemented by any of a number of different arrangements. The server 302 and a navigation device 200 can communicate when a connection via communications channel 318 is established between the server 302 and the navigation device 200 (noting that such a connection can be a data connection via mobile device, a direct connection via personal computer via the internet, etc.).

The server 302 includes, in addition to other components which may not be illustrated, a processor 304 operatively connected to a memory 306 and further operatively connected, via a wired or wireless connection 314, to a mass data storage device 312. The processor 304 is further operatively connected to transmitter 308 and receiver 310, to transmit and send information to and from navigation device 200 via communications channel 318. The signals sent and received may include data, communication, and/or other propagated signals. The transmitter 308 and receiver 310 may be selected or designed according to the communications requirement and communication technology used in the communication design for the navigation system 200. Further, it should be noted that the functions of transmitter 308 and receiver 310 may be combined into a signal transceiver.

Server 302 is further connected to (or includes) a mass storage device 312, noting that the mass storage device 312 may be coupled to the server 302 via communication link 314. The mass storage device 312 contains a store of navigation data and map information, and can again be a separate device from the server 302 or can be incorporated into the server 302.

The navigation device 200 is adapted to communicate with the server 302 through communications channel 318, and includes processor, memory, etc. as previously described with regard to Fig. 2, as well as transmitter 320 and receiver 322 to send and receive signals and/or data through the communications channel 318, noting that these devices can further be used to communicate with devices other than server 302. Further, the transmitter 320 and receiver 322 are selected or designed according to communication requirements and communication technology used in the communication design for the navigation device 200 and the functions of the transmitter 320 and receiver 322 may be combined into a single transceiver.

Software stored in server memory 306 provides instructions for the processor 304 and allows the server 302 to provide services to the navigation device 200. One service provided by the server 302 involves processing requests from the navigation device 200 and transmitting navigation data from the mass data storage 312 to the navigation device 200. Another service provided by the server 302 includes processing the navigation data using various algorithms for a desired application and sending the results of these calculations to the navigation device 200.

The communication channel 318 generically represents the propagating medium or path that connects the navigation device 200 and the server 302. Both the server 302 and navigation device 200 include a transmitter for transmitting data through the communication channel and a receiver for receiving data that has been transmitted through the communication channel.

The communication channel 318 is not limited to a particular communication technology. Additionally, the communication channel 318 is not limited to a single communication technology; that is, the channel 318 may include several communication links that use a variety of technology. For example, the communication channel 318 can be adapted to provide a path for electrical, optical, and/or electromagnetic communications, etc. As such, the communication channel 318 includes, but is not limited to, one or a combination of the following: electric circuits, electrical conductors such as wires and coaxial cables, fibre optic cables, converters, radio-frequency (RF) waves, the atmosphere, empty space, etc. Furthermore, the communication channel 318 can include intermediate devices such as routers, repeaters, buffers, transmitters, and receivers, for example.

In one illustrative arrangement, the communication channel 318 includes telephone and computer networks. Furthermore, the communication channel 318 may be capable of accommodating wireless communication such as radio frequency, microwave frequency, infrared communication, etc. Additionally, the communication channel 318 can accommodate satellite communication. The communication signals transmitted through the communication channel 318 include, but are not limited to, signals as may be required or desired for given communication technology. For example, the signals may be adapted to be used in cellular communication technology such as Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Code Division Multiple Access (CDMA), Global System for Mobile Communications (GSM), etc. Both digital and analogue signals can be transmitted through the communication channel 318. These signals may be modulated, encrypted and/or compressed signals as may be desirable for the communication technology.

The server 302 includes a remote server accessible by the navigation device 200 via a wireless channel. The server 302 may include a network server located on a local area network (LAN), wide area network (WAN), virtual private network (VPN), etc.

The server 302 may include a personal computer such as a desktop or laptop computer, and the communication channel 318 may be a cable connected between the personal computer and the navigation device 200. Alternatively, a personal computer may be connected between the navigation device 200 and the server 302 to establish an internet connection between the server 302 and the navigation device 200. Alternatively, a mobile telephone or other handheld device may establish a wireless connection to the internet, for connecting the navigation device 200 to the server 302 via the internet.

The navigation device 200 may be provided with information from the server 302 via information downloads which may be periodically updated automatically or upon a user connecting navigation device 200 to the server 302 and/or may be more dynamic upon a more constant or frequent connection being made between the server 302 and navigation device 200 via a wireless mobile connection device and TCP/IP connection for example. For many dynamic calculations, the processor 304 in the server 302 may be used to handle the bulk of the processing needs, however, processor 210 of navigation device 200 can also handle much processing and calculation, oftentimes independent of a connection to a server 302.

As indicated above in Fig. 2, a navigation device 200 includes a processor 210, an input device 220, and a display screen 240. The input device 220 and display screen 240 are integrated into an integrated input and display device to enable both input of information (via direct input, menu selection, etc.) and display of information through a touch panel screen, for example. Such a screen may be a touch input LCD screen, for example, as is well known to those of ordinary skill in the art. Further, the navigation device 200 can also include any additional input device 220 and/or any additional output device 241 , such as audio input/output devices for example.

Figs 4A and 4B are perspective views of a navigation device 200. As shown in Fig. 4A, the navigation device 200 may be a unit that includes an integrated input and display device 290 (a touch panel screen for example) and the other components of fig.

2 (including but not limited to internal GPS receiver 250, microprocessor 210, a power supply, memory systems 230, etc.).

The navigation device 200 may sit on an arm 292, which itself may be secured to a vehicle dashboard/window/etc, using a suction cup 294. This arm 292 is one example of a docking station to which the navigation device 200 can be docked.

As shown in Fig. 4B, the navigation device 200 can be docked or otherwise connected to an arm 292 of the docking station by snap connecting the navigation device 292 to the arm 292 for example. The navigation device 200 may then be rotatable on the arm 292, as shown by the arrow of Fig. 4B. To release the connection between the navigation device 200 and the docking station, a button on the navigation device 200 may be pressed, for example. Other equally suitable arrangements for coupling and decoupling the navigation device to a docking station are well known to persons of ordinary skill in the art.

As discussed above, the navigation device 200 receives GPS satellite signals

160 from a plurality of satellites 120 to calculate its position, or current location. When the navigation device 200 is moving, for example by being mounted in a moving vehicle, the current location is regularly recalculated and on-screen information, such as map and/or route information, updated accordingly. During navigation, the reception of GPS satellite signals 160 from one or more satellites 120 may be temporarily lost, resulting in the navigation device 200 being unable to accurately determine its current location. This causes problems when the user requires information about the current location or route whilst the GPS signal 160 is lost.

In order to overcome this, an accelerometer, which is typically mounted inside the navigation device 200, can be used to facilitate dead reckoning of the navigation device's current location. The accelerometer measures the acceleration experienced by the navigation device 200. Acceleration is linked to velocity by the equation: dv a⁼ dϊ where a is acceleration, v is velocity, and t is time. Using knowledge about the velocity of movement and time taken, the processor 210 is operable to calculate a new current location from the last location measured by receiving the GPS signal 160. Navigation using information about speed and time of travel is known as dead reckoning. However, a problem has been noted in that if the navigation device 200 is subject to pitch by, for example, being moved along a gradient, then the measured acceleration is subject to an error. The error results from an effect of gravity on the accelerometer. When subject to a pitch, the effect of gravity upon acceleration is given by:

g' = g s\n{0) where g' is measured gravity, g is gravity which is around 9.82 m/s² and θ is the pitch angle. Thus, as the navigation device 200 inclines, the accelerometer measures a change in acceleration, due to the effect of pitch angle, even when the navigation device 200 is not subject to a change in velocity. The output of the accelerometer is fully given by the equation:

_ dv a⁼ Ε + 9 sin(©)

The navigation device 200, when subject to changes in pitch angle, incorrectly calculates a change in velocity and will consequently assume an incorrect location after a period of time.

In order to overcome this problem, embodiments of the present invention use knowledge of pitch angle to more accurately determine acceleration. Embodiments of the present invention utilise altitude information to determine the pitch angle, whilst other embodiments of the present invention utilise stored or obtained pitch information.

A first embodiment of the present invention will now be described. Unless otherwise described, the illustrated embodiment of navigation device 500 comprises like parts to those shown in Figure 2.

As shown in Figure 5, a navigation device 500 comprises an altimeter 501 operatively connected to a processor 510 to receive altitude information 505 measured by the altimeter 501. The altimeter 501 is preferably a pressure altimeter which measures air pressure, calculates the current altitude and provides altitude information 505 to the processor 510. When the navigation device 500 moves along a gradient, the altitude changes and the processor 510 receives time-variant altitude information 505.

Using the altitude information 505, the processor 510 is able to calculate a pitch angle representing a gradient at the navigation device's current location. The pitch angle is a value of pitch angle θ to which the navigation device 500 is subjected and is calculated using the following equation:

__χ /ΔαZtitude\ ø = tan \Δdistance)

Using the pitch angle for the current location, the processor 510 is able to correct, or normalise, acceleration information 515 provided by an accelerometer 502, which is operatively connected to the processor 510 to receive the acceleration information 515. That is, with knowledge of θ, or the pitch angle, the effect of gravity on the accelerometer may be corrected, such that the measured acceleration more accurately represents the acceleration applied to the accelerometer 502 and the navigation device 500, rather than a change in measured gravity due to varying pitch angle.

Figure 6 shows a method 600 according to an embodiment of the present invention for correcting a dead reckoning calculation.

The method begins at step 601. In step 602 the navigation device 500 receives GPS signals 160 to calculate its current location. In step 603, it is determined if the GPS signal 160 has been lost. That is, whether any GPS signal 160 is received and if it is possible to determine the current location from the received GPS signal 160. If it is determined that the GPS signal has been lost, the altimeter 501 measures the current altitude and provides altitude information 505 to the processor 510. It will be realised, however, that the processor 510 may receive altitude information 505 from the altimeter 502 even whilst the GPS signal is received.

In step 604, an altitude at a first location is measured using the altimeter 501. In step 605, an altitude at a second location is measured. A distance between the altitude measurements may be determined, at least approximately, by knowledge of the velocity at which the navigation device 500 was last moving before the GPS signal 160 was lost. The velocity may be further approximated using acceleration measurements made between the first and second altitude measurements. In step 606 the pitch angle θ is calculated using the altitude measurements, as explained above. In step 607, the pitch angle is used to calculate acceleration experienced by the navigation device 500, corrected for pitch θ, and also the velocity of the navigation device's movement. In step 608 a new position of the navigation device 500 is calculated based upon velocity and time of movement using dead reckoning. Since the pitch angle is known, acceleration information 505 from the accelerometer 502 may be corrected to provide a more accurate value of acceleration and, hence, calculated velocity of determining movement for the navigation device 500.

However, altitude measurements made using pressure altimeters in environments in which navigation devices 500 operate may be unreliable. For example, GPS signals 160 are expected to be lost by the navigation device 500 when travelling through a tunnel. In this situation, dead reckoning of a current location within the tunnel is used. It is also common for tunnels, such as those under rivers or in mountainous regions, to be subjected to inclines or declines which, as explained above, introduce errors into measured acceleration. However, it may be difficult to make accurate pressure altimeter measurements in such an environment due to air flow within the tunnel, air disturbances caused by passing vehicles etc. Use of incorrect altitude information will consequently affect the calculated pitch angle, acceleration, velocity and, in turn, location obtained via a dead reckoning calculation.

In order to overcome or reduce this, in one embodiment, the processor 510 is arranged to store in a memory 530 information for correcting measured acceleration. In one embodiment, the processor stores measured altitude information in the memory 530, whilst in another embodiment the processor 510 stores a calculated pitch angle in the memory 530. For example, the processor 510 stores altitude information for the current location in pairs (altitude; location) or stores pitch angle for the current location (gradient; location). If it is determined over a plurality of samples that the gradient of a region varies rapidly, then an increased number of samples per unit distance may be stored. Alternatively, if a constant gradient region is encountered, then the number of samples stored per unit distance may be reduced.

Using the stored information in combination with measured altitude can be utilised improve an accuracy of acceleration measurement. In one embodiment, measured altitude information for a location may be averaged with stored altitude information for the location. The sampling of altitude information a plurality of times at each location improves an accuracy of the stored altitude information. Similarly, stored pitch angle information can be handled in the same way to gradually improve an accuracy of the stored information.

Figure 7 shows a method 700 of using and updating stored information. The method begins in step 701. In step 702, it is determined if altitude information is already stored in the memory 530 for the current location. If no stored information exists, then in step 705, measured altitude information is stored in the memory 530 for the current location. In step 706 the measured altitude information is used as described above to calculate a pitch angle at the current location and to correct measured acceleration. If, in step 702, altitude information exists for the current location, the measured altitude information is used in combination with the stored altitude information to improve an accuracy of the inclination information and, consequently, the dead reckoning calculation using measured acceleration. In step 704 the stored information is updated in the memory 530 to further improve accuracy of future calculations.

In an alternative embodiment, in order to reduce the amount of stored data, stored information is replaced with an approximation of an incline. For example, a plurality of stored incline information samples may be fitted with a function which approximates the incline. A suitable function is a spline.

In other embodiments, information about a current location is obtained in order to improve a dead reckoning calculation.

In one embodiment, altitude or pitch angle information may be stored in the memory 530 alongside, or as part of, map data. When the navigation device 500 is unable to obtain a GPS signal 160, the stored altitude or pitch angle information is utilised in order to improve a dead reckoning calculation by correcting measured acceleration for inclined or declined movement. In another embodiment, altitude or pitch angle information is obtained from the server 302 via the communications channel 318.

Figure 8 shows a method according to an embodiment of the present invention which method begins with step 801. In step 802 the navigation device 500 receives the GPS signal 160 to determine a current location. In step 803, it is determined if the GPS signal has been lost. If the GPS signal has been lost, then in step 804 altitude or pitch angle information for the current location is obtained. As discussed above, the information may be obtained from amongst or alongside map data stored in the memory 530, or from the server 302. The obtained altitude or pitch angle information is then used in step 805 to correct measure acceleration information and to consequently improve a dead reckoning calculation by reducing the error associated with acceleration measurements.

It will be apparent from the foregoing that the teachings of the present invention provide a navigation device and method for use in a navigation device which imrove an accuracy of navigation during periods when a GPS signal is lost. During these periods, dead reckoning calculations may be performed based upon information obtained from an accelerometer which is corrected for an effect of gravity.

It will also be appreciated that whilst various aspects and embodiments of the present invention have heretofore been described, the scope of the present invention is not limited to the particular arrangements set out herein and instead extends to encompass all arrangements, and modifications and alterations thereto, which fall within the scope of the appended claims.

For example, whilst embodiments described in the foregoing detailed description refer to GPS, it should be noted that the navigation device may utilise any kind of position sensing technology as an alternative to (or indeed in addition to) GPS. For example the navigation device may utilise using other global navigation satellite systems such as the European Galileo system. Equally, it is not limited to satellite based but could readily function using ground based beacons or any other kind of system that enables the device to determine its geographic location.

It will also be well understood by persons of ordinary skill in the art that whilst the preferred embodiment implements certain functionality by means of software, that functionality could equally be implemented solely in hardware (for example by means of one or more ASICs (application specific integrated circuit)) or indeed by a mix of hardware and software. As such, the scope of the present invention should not be interpreted as being limited only to being implemented in software.

Lastly, it should also be noted that whilst the accompanying claims set out particular combinations of features described herein, the scope of the present invention is not limited to the particular combinations hereafter claimed, but instead extends to encompass any combination of features or embodiments herein disclosed irrespective of whether or not that particular combination has been specifically enumerated in the accompanying claims at this time.

Claims

1. A navigation device (500) comprising:

a processor (510); and

an accelerometer (500) arranged to output measured acceleration information to the processor (510);

characterised in that:

the processor (510) is arranged to correct the measured acceleration information for an effect of gravity by utilising pitch angle information.

2. The navigation device of claim 1 , wherein the processor is arranged to determine the acceleration by subtracting the effect of gravity g' from the measured acceleration according to the equation:

g' = g sin(ø)

wherein θ is pitch angle and g is gravity.

3. The navigation device of claim 1 or 2, wherein the pitch angle information is obtained from altitude information.

4. The navigation device of claim 3, wherein the pitch angle information is obtained using the equation:

Δaltitude\

0 = tan

' (: Δdistance)

5. The navigation device of claim 3 or 4, comprising an altimeter (501 ) arranged to output the altitude information (505) to the processor (510).

6. The navigation device of claim 3 or 4, wherein the altitude information is obtained from a data storage device or a server (302).

7. The navigation device of any of any preceding claim, wherein the processor (510) is arranged to store pitch angle information or measured altitude information in a memory (530).

8. The navigation device of claim 7, wherein the processor (510) is arranged to determine if stored information exists in the memory (530) for a current location and to utilise the stored information in combination with measured altitude information to determine the pitch angle.

9. The navigation device of claim 8, wherein the processor (510) is arranged to update the stored information following determination of the pitch angle.

10. The navigation device of claim 7, 8 or 9, wherein the processor is arranged to store the altitude information as a function representing altitude along a route.

11. The navigation device of claim 1 or 2, wherein the pitch angle information is obtained from a data storage medium or via a server.

12. A method for use in a navigation device (500), comprising:

measuring acceleration of a navigation device (500);

characterised by:

correcting the measured acceleration for an effect of gravity by utilising pitch angle information;

determining a velocity of the navigation device (500);

updating a current location using the determined velocity.

13. The method of claim 12, wherein the correcting of the measured acceleration comprises subtracting an effect of gravity from the measured acceleration.

14. The method of claim 12 or 13, comprising:

determining a first altitude of the navigation device (500) at a first location; determining a second altitude of the navigation device at a second location;

determining the pitch angle information with respect to the first and second altitudes.

15. The method of claim 14, comprising storing altitude information in a storage device.

16. The method of claim 14 or 15, wherein the determining of the first or second altitudes comprises determining if stored altitude information exists for the first or second location.

17. The method of claim 16, comprising updating the stored altitude information according to measured altitude information.

18. The method of any of claims 15 to 17, comprising approximating a plurality of stored altitude information values with a function.

19. The method of claim 12, comprising determining the pitch angle information from information obtained from one of a storage device (530) or a server (302).

20. A storage medium comprising computer executable instructions which, when executed upon a processor, cause the processor to perform the method of any of claims 12 to 19.