GB2388195A - Navigational instrumentation and display - Google Patents

Navigational instrumentation and display Download PDF

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Publication number
GB2388195A
GB2388195A GB0221308A GB0221308A GB2388195A GB 2388195 A GB2388195 A GB 2388195A GB 0221308 A GB0221308 A GB 0221308A GB 0221308 A GB0221308 A GB 0221308A GB 2388195 A GB2388195 A GB 2388195A
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United Kingdom
Prior art keywords
heading
magnetic
compass
navigation
display
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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GB0221308A
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GB0221308D0 (en
Inventor
Martin Poole
Tim Robson
David Bain
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TRUNOR DESIGNS Ltd
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TRUNOR DESIGNS Ltd
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Publication date
Priority to GB0210131A priority Critical patent/GB0210131D0/en
Priority to GB0218052A priority patent/GB0218052D0/en
Application filed by TRUNOR DESIGNS Ltd filed Critical TRUNOR DESIGNS Ltd
Publication of GB0221308D0 publication Critical patent/GB0221308D0/en
Priority claimed from GB0424058A external-priority patent/GB2403297B/en
Publication of GB2388195A publication Critical patent/GB2388195A/en
Withdrawn legal-status Critical Current

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Classifications

    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C17/00Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes
    • G01C17/02Magnetic compasses
    • G01C17/28Electromagnetic compasses
    • G01C17/30Earth-inductor compasses
    • GPHYSICS
    • G01MEASURING; TESTING
    • G01CMEASURING DISTANCES, LEVELS OR BEARINGS; SURVEYING; NAVIGATION; GYROSCOPIC INSTRUMENTS; PHOTOGRAMMETRY OR VIDEOGRAMMETRY
    • G01C17/00Compasses; Devices for ascertaining true or magnetic north for navigation or surveying purposes
    • G01C17/38Testing, calibrating, or compensating of compasses

Abstract

A navigation apparatus for assisting a user in the steering of a craft is described. The apparatus comprises: processing means arranged to receive a magnetic compass signal from a magnetic compass indicating the magnetic field direction at a current geographic location and to generate navigational data corresponding to the magnetic field direction. The apparatus also comprises display means arranged to generate and display a rotatable image of a compass, to be responsive to the navigational data received from the processing means to orient the compass image with respect to a current heading marker on the display, and to display a graphical image showing a pre-programmed course to steer in relation to the compass image. The image is displayed such that any difference between the course to steer and the current heading can readily be determined graphically by the use of the apparatus.

Description

23881 95
( IMPROVEMENTS RELATING TO
NAVIGATIONAL INSTRUMENTATION
The present invention concerns improvements relating to navigational instrumentation s for navigating small to medium-sized craft and provides, more specifically, though not exclusively, a compass apparatus whose graphical interface incorporates representations of standard navigational equipment which allow a navigator to direct their craft intuitively and with improved accuracy.
lo As the ownership of leisure vessels and light aircraft increases, so does the need for navigation equipment, which is more user friendly. Although many new owners of such craft may think that a decent compass and map are all that will be required to get them to their chosen destination, they will have failed to appreciate the significance of the Earth's molten core and its magnetic field.
Whenever a compass is moved, its permanently magnetised needle will rotate until it becomes realigned with the Earth's magnetic field. At the Earth's surface, the
magnetic field is similar to that which would be obtained if a bar magnet had been
placed at the Earth's centre. Accordingly, over much of the Earth's surface the aligned zo compass needle will point in the general direction of the North Pole (hence the use of the compass as a common navigation tool). However, the actual direction indicated by a compass needle is magnetic north as opposed to geographic north and the To can vary by several degrees. This can cause problems when accurate navigation is required: the vertical grid lines on a map are aligned with geographic north, whilst the compass 25 which is used to set a bearing aligns itself with magnetic north.
Accordingly for accurate navigation, a correction needs to be made when translating from map to compass. The difference between geographic north and magnetic north is referred to as variation and can alter with position on the Earth's surface and over 30 time, according to complex fluid motion within the Earth's outer core. In addition, the alignment of a compass may also be affected by magnetic fields within its locality, for
( example magnetic materials from which a craft is built or which have been brought onboard. The overall effect of these local fields varies according to the craft's
orientation with respect to the Earth's predominantly north magnetic field. This second
type of aberration is known as deviation. Hence, two corrections are required in s determining an accurate compass bearing.
On large commercial craft, relatively accurate compass alignment with geographic north can be achieved through the use of gyrostabilisors. Gyrostabilised platforms are used on ships, but these are too heavy, cumbersome and expensive for smaller leisure lo vessels/craft. Similarly, commercial aeroplanes are fitted with electronic gyroscopic compasses, but again these are expensive to fit in light aircraft. Instead, relatively low cost navigation systems using the global positioning system (GPS) can now provide variation values to leisure craft, whilst a table of deviation values across the full range of 360 headings should ideally be produced on an individual basis for each craft.
is However, navigation systems using the GPS rely on a network of Earthorbiting satellites, with each satellite covering a terrestrial area of a hundred square metres or so. If a leisure vessel/craft is travelling slowly, it may remain in the same satellite's geographic zone for some time and misleadingly be categorised as having a stationary 20 position; in this situation, the error in position becomes comparatively large with respect to the distance travelled. For this reason, when accurate navigation at slow speeds is required such navigation systems need to be disengaged once a value for the local variation has been obtained, for example when navigating through a rocky chaMel to a harbour entrance.
Production of a table of deviations for a craft is expensive as it requires the services of a compass adjuster for several hours. A craft can be aligned with geographical north using local landmarks and then steered through a 360 course at a constant rate, such that readings of magnetic north (with respect to geographic north) can be taken at so predetermined intervals coinciding with each heading. Using the local value for variation, a table of deviations can be calculated for each of the 360 headings.
( However, even if a table is produced it places onerous restrictions on the craft's owner, since the deviation values have to be re-calibrated if the craft's compass is replaced or if any object with a magnetic influence is brought onboard thereafter or moved. Given this and the scarcity of compass adjusters, it seems that many leisure craft owners are 5 failing to correct for deviation errors and are sailing or flying without optimum accuracy. Nevertheless, those who do take the above steps face an additional problem - namely making the corrections by mental arithmetic. Instrumentation using the Global lo Positioning System (GPS) provides 8 numeric value for variation (providing magnetic north with respect to geographic north), to which the predetermined deviation value must either be added or subtracted (resulting in north as indicated by the magnetic compass). The map bearing then needs to be corrected by the resulting amount, so that the pilot or helmsman finally arrives at a bearing, which is suitable for use with the 5 magnetic compass.
This problem has been addressed by some of the more modern Fluxgate compasses, which contain one or more soft iron cores surrounded by coils. A small microprocessor system can be used to convert analogue data from the Fluxgate into a stream of digital So information, which can be combined with location data received from the GPS. The pilot or helmsman is then presented with a numeric heading value relative to geographic north on a digital display, which can be used with bearings taken directly from a map. In addition, such analogue-to-digital compasses can also be configured to calibrate 'automatically' a table of deviations.
2s However, even modern Fluxgate compasses are still difficult to use for the following reasons. Providing only a numeric readout of a craft's geographic heading fails to assist the pilot or helmsman in his or her environment. If the geographic heading does not equal the desired bearing, then the pilot or helmsman will need to make an 30 adjustment. The direction in which the steering wheel should be fumed though is not readily apparent when out at sea, in mid-air or in unfamiliar surroundings. In short, the
modern compass does nothing to work with the pilot or helmsman's intuition. In addition, the 'automatic' deviation calibration procedure still requires a boat or aircraft to be taken through a course of 360 , at the pilot or helmsman's instigation. As indicated previously, such calibration procedures ought to be performed every time an s object with a magnetic influence is either moved or brought onboard, but very rarely are. It is desired to overcome or substantially reduce at least some of the above-mentioned problems. More specifically, it is desired to provide a compass apparatus that performs lo image processing to produce an intuitive graphical interface, which assists with navigation. In addition, it is also desired to provide a fully automatic deviation calibration device, namely one that does not require the pilot to navigate 360 to obtain a valid set of readings.
5 According to one aspect of the present invention there is provided a navigation apparatus for assisting a user in the steering of a craft, the apparatus comprising: processing means arranged to receive a magnetic compass signal from a magnetic compass indicating the magnetic field direction at a current geographic location and to
generate navigational data corresponding to the magnetic field direction; and display
20 means arranged to generate and display a rotatable image of a compass, to be responsive to the navigational data received from the processing means to orient the compass image with respect to a current heading marker on the display, and to display a graphical image showing a pre- programmed course to steer in relation to the compass image such that any difference between the course to steer and the current 25 heading can readily be determined graphically by the use of the apparatus.
The present invention therefore provides a navigational apparatus that can advantageously provide an instantaneous graphical view of a current heading and also a desired heading both with respect to a graphical image of a compass. This inevitably 30 makes the use of this instrument far more intuitive and easier to read than has been
( possible previously. This also minimises the level of human error, which occurs when using the prior art numerical heading and course to steer readouts.
Preferably, the display means is arranged to display at least one direction symbol 5 indicating, with reference to the current heading marker, the direction to steer the craft in order to reduce any difference between the current heading and the pre-programmed course to steer. This feature provides the user with specific infomnation as to the direction to turn the craft. Whilst this may at first seem trivial, one has to appreciate that the fuming of a craft can be counter intuitive, for example on a boat with a tiller, pushing the lo tiller handle to the right (starboard) with actually turn the boat to the left (port). The provision of at least one direction symbol makes the issue of which way to turn the steering mute by giving the navigator or helmsman a specific direction in which to turn the wheel or steering control. This of course can be readily reset by the processing means to ensure that both intuitive and counter-intuitive steering can be accommodated 5 depending on the type of craft being used.
The processing means may also be arranged to generate a difference signal which indicates the degree of the difference between the current heading and the course to steer, and the display means may be arranged to modify the at least one direction 20 symbol in response to receipt of the difference signal such that the degree of difference is graphically indicated to the user. This provides the user with an idea of how severe the current steering action is required to get back on course and thereby further assists in helping the user with control of the steering of the craft. If the degree of the difference exceeds a predetermined threshold, an audible alarm can be generated by 25 the processing means to draw the navigator's attention to the navigation display.
Preferably the at least one direction symbol is coloured differently depending on the direction indicated to steer. This further assists in the recognition and differentiation of the different ways to turn. In one exemplary embodiment, the at least one direction 30 symbol comprises a left tum symbol and a right tum symbol and the left turn direction symbol is displayed as a red symbol and the right turn direction symbol is displayed as a s
( green symbol. This is in line with conventional colour codes used for maritime port and starboard turns.
The display means may be arranged to generate and display numerical symbols s indicating the current heading and the pre-programmed course to steer. The provision of numerical displays in combination with the graphical display gives a user an opportunity to have a very accurate knowledge of the actual course to steer or heading for steering if required. This itself means that the user does not necessarily have to read off the markings on the graphical display to determine the actual value of the heading lo or course to steer. Advantageously, the numerical symbols indicating the current heading and the pre-prograrnmed course to steer are displayed adjacent each other to further assist user comparison.
Preferably the display means is arranged to generate and display a rotatable three-
dimensional simulation of a compass. This simulation is highly beneficial in that the user is presented with a three-dimensional image of a compass that is similar to what he or she would see when looking at a real navigational compass. This emulation, is the most effective at minimising the time taken to learn how to use the navigation apparatus because most users will already know how to read an standard compass.
20 Furthermore it also provides the most comfortable image for viewing as has been determined from tests. As part of this simulation, the display means may be arranged to generate and display the simulation of the compass as viewed from an acute angle to the plane of rotation of the compass. Again, this feature further assists in providing a more realistic simulation in that most normal ships compasses, for example, are 25 mounted vertically and viewed at an acute angle to the plane of rotation.
The present navigation apparatus may be configured to allow for situations where the actual heading and the course over ground are not actually the same. More specifically, the display means may be arranged to display a zone image placed in relation to the 30 compass image, the zone image indicating the degree of difference between the current heading and an actual course over ground of the craft. This gives the navigator the
( advantageous ability to determine whether he or she should take any action in changing the control of the craft. For example, is the degree of difference sufficient to merit a change of tack (if in a sailing boat).
s Preferably the display means is arranged to move the graphical course to steer image at a visibly noticeable rate from an existing course to steer heading to a new course to steer heading. This enables the navigator to see how dramatic changes in direction should be followed and also enables the navigator to know why the course to steer marker is about to disappear. Furthermore the display means may be arranged to move the graphical lo course to steer image at a predetermined visible rate such that the user can steer the craft at the same rate by keeping the current heading of the craft and the course to steer marker in a constant relational position to each other. Clearly this has benefits for novice pilots and helmsmen in that they can use the navigation apparatus to effect smooth turns at a constant rate without a great deal of experience of how these manoeuvres are achieved.
According to another aspect of the present invention there is provided a method of assisting a user in the steering of a craft, the method comprising: receiving a magnetic compass signal from a magnetic compass indicating the magnetic field direction at a
current geographic location; generating navigational data corresponding to the 20 magnetic field direction; generating and displaying a rotatable image of a compass;
orienting the compass image with respect to a current heading marker on the display in response to the navigational data; and displaying a graphical image showing a pre-
programmed course to steer in relation to the compass image such that any difference between the course to steer and the current heading can readily be determined 25 graphically.
The above method has the same advantages as have been described above in relation to the corresponding navigation apparatus and so are not repeated here.
30 According to another aspect of the present invention there is provided an interactive navigation tool for assisting a user in the steering of a craft, the tool being arranged to
( generate navigational data corresponding to a sensed magnetic field direction; and
comprising display means arranged to generate and display a rotatable three-
dimensional simulation of a compass, the display means being responsive to the navigational data to orient the compass simulation with respect to a current heading s marker on the display, and being arranged to display a graphical symbol indicating to the user a direction to steer in order to unify the current heading and a pre-prograrnmed course to steer graphical image generated and displayed on the display means.
The combination of a three-dimensional simulation of a compass together with the lo graphical symbols indicating a direction to steer, results in a synergistic apparatus that is extremely beneficial to the navigator. The navigator adapts readily to the use of a display' which is in a familiar format, together with extra symbols that give him or her specific directions as to how to steer the craft. Navigation and control of the craft is made significantly easier by these features.
According to another aspect of the present invention there is provided a method of assisting a user in the steering of a craft, the method comprising: generating navigational data corresponding to a sensed magnetic field direction; generating and
displaying a rotatable three-dimensional simulation of a compass; orienting the 20 compass simulation with respect to a displayed current heading marker in response to the navigational data; and displaying a graphical symbol indicating to the user a direction to steer in order to unify the current heading and a pre-programmed course to steer graphical image generated and displayed on the display means.
2s The above method has the same advantages as have been described above in relation to the corresponding navigation tool and so are not repeated here.
The present invention also extends to a method of determining a corrected geographic heading for a craft, the method comprising: receiving current location information 30 from a geographic position determining device, magnetic-derived heading information from a magnetic compass device and condition information representative of the
( conditions under which the magnetic heading information has been received; generating a position-derived heading information of the craft from the current location information received over a given time period; correcting the magnetic-
derived heading infonnation for magnetic deviation by use of a pre-stored table of s magnetic deviation values for the craft; comparing the corrected direction information with the position-derived heading information; and, in the event of a difference and if the condition information validates the magnetic-derived heading information by showing a relatively steady state, updating the table of deviations with a deviation value calculated to remove the difference.
This aspect of the present invention provides an improvement to the socalled automatic' deviation calibration procedure, which has been described in relation to the prior art. With this aspect of the present invention, there is no need for the onerous
requirement in re-calibrating the entire table of deviations by taking the boat or aircraft 15 through a course of 360 and measuring the magnetic deviation at each heading.
Rather, by monitoring the conditions under which the magnetic-derived heading has been obtained, a judgement can be made as to the validity of the stored deviation value for the current heading. This is possible because a position-derived heading is also obtained, such that a difference between the position-derived and magnetic-derived 0 headings can be obtained and corrected by updating the relevant entry in the table of deviations so that they correspond.
The benefit of not having to be taken through a 360 turn in order to recalibrate the deviation value is significant. It means that the updating becomes truly automatic in 2s that it does not require any action by the navigator to effect re-calibration. Being independent of the navigator's actions means that the deviation is re-calibrated more often and hence the headings displayed on the navigation device are more accurate for more of the time.
30 The method preferably further comprises determining the magnetic variation of the current location information, and correcting both the position-derived heading
( information and the corrected magnetic-derived heading information for magnetic variation. In this way, a true heading with respect to geographic north corrected for both magnetic deviation and variation can be obtained. This further improves the accuracy of the current heading generated.
s Preferably the method further comprises determining whether a leeway mode of operation has been selected prior to the adjusting step, thereby indicating that there is a difference between the heading and a course over ground of the craft. This step acts as a filter to determine whether the deviation updating can occur. Clearly, if the craft is not lo travelling in the direction it is pointing (the current heading is not equal to the course over ground) then updating the deviation table automatically will contain an undesirable error. Preferably the condition information includes speed of the craft over a predetermined 5 time period and/or the period over which the current magnetic-derived heading has been held. These conditions indicate a relatively stable state of the craft thereby validating the magnetic-derived heading that has been taken. Other conditions may also be used so long as they also validate the magnetic-derived heading.
20 This aspect of the present invention may also be considered to relate to a navigation device for determining a corrected geographic heading for a craft, the device comprising: processing means arranged to receive current location information from a geographic position determining device, magnetic-derived heading information from a magnetic compass device and condition information representative of the physical 25 conditions under which the magnetic heading information has been received; and to generate a position-derived heading of the craft from the current location information received over a given time period; the processing means being further arranged: to correct the magnetic-derived heading information for magnetic deviation by use of a pre-stored table of magnetic deviation values for the craft; and to compare the 30 corrected heading information with the position-derived heading and, in the event of a difference, to adjust an appropriate deviation value in the table of deviation values to
( remove the difference, if the condition information validates the magnetic-derived heading information by showing a relatively steady state.
Methods and apparatus according to preferred embodiments of the improved compass 5 invention are now described by way of example, with reference to the accompanying drawings in which: Figure 1 is a schematic block diagram showing a navigation system, including a virtual compass interface, for use in implementing an exemplary embodiment of the present lo invention; Figure 2 is a schematic block diagram showing a subsection of the navigation system of Figure 1 in greater detail; 5 Figures 3a, 3b and 3c are graphical representations of exemplary outputs from the virtual compass interface of Figure 1; Figure 4 is an example of the output from the virtual compass interface of Figure 1 when operating in leeway mode; Figure 5 is a plan view of a typical harbour entrance, showing the navigational buoys to which a helmsman must navigate for use in describing how the present embodiment may be utilised; 25 Figures 6a, 6b and 6c are examples of the output from the virtual compass interface of the present embodiment whilst a helmsman attempts to navigate to the first of the navigational buoys shown in Figure S; Figure 7 is a flow diagram showing the steps involved in a navigation process of 30 outputting data to the virtual compass interface and performing automatic calibration of deviation data;
( Figures ga and 8b show the relationship between geographic north, magnetic north and compass north (as indicated by a magnetic compass) for an example heading processed according to the flow diagram of Figure 7, for cases where no deviation calibration is s required and where deviation calibration is required, respectively; and Figure 9 is a flight path diagram showing a typical racetrack hold pattern which can be accurately flown by an aircraft using a turn rate assistance feature of a further embodiment of the present invention.
With reference to Figure 1, a navigation system log for implementing presently preferred embodiments of the present invention is now described. The navigation system 100 provides an intuitive compass interface, in the geographic north frame of reference, which assists a pilot or helmsman in navigation of their craft. In addition, is the navigation system 100 is also able to update deviation values automatically, as and when necessary, on an individual heading basis.
The navigation system 100 is composed of a data processor 102 which receives input data from Global Positioning System (GPS) instrumentation 104 and a Fluxgate JO compass 106 and outputs navigational data 107 to a virtual compass interface 108. A helmsman or pilot 110 refers to the virtual compass interface 108 for assistance when guiding their craft using a steering device 112. The navigational data 107, which is processed by the microprocessor 102 and output graphically to the virtual compass interface 108, includes a pre-prograrnmed bearing, or course to steer, with respect to 25 geographic north and a present heading of the craft (not shown) also with respect to geographic north. The virtual compass interface 108 also indicates a calculated the direction in which corrective steering should be made. As the craft moves under the steerage of the helmsman or pilot llO, so its position as detected by the GPS instrumentation 104 changes and is fed back into the data processor 102' resulting in a 30 possible change of heading and direction of corrective steering. All this gives rise to an iterative processing loop based on feedback.
( Figure 2 shows the inputs to and outputs from the data processor 102 in more detail.
The data processor 102 is comprised of a microprocessor system 200, a read only memory 202 and a display driver 204. A software program (not shown), stored in the 5 read only memory 202, is used by the microprocessor system when processing inputs from the GPS instrumentation 104 and the Fluxgate compass 106. This processing will be described in detail in due course, but briefly the microprocessor system 200 extracts a value for the local variation from the input received from GPS instrumentation 104, combines this with a magnetic heading corrected for deviation provided by the l o Fluxgate compass 106 and then compares the resulting sum with the heading indicated by the GPS instrumentation 104 with respect to geographic north. If the two values are different, then the microprocessor system 200 investigates whether an automatic calibration of the deviation value for the present heading is required.
Is Returning to Figure 2, the virtual compass interface 108 has different modes of operation and the helmsman or pilot 110 can select their preferred mode by means of a button control panel 206 or other user inte', face, which is then transmitted as an additional input to the microprocessor system 200. Data concerning the processing results and mode of operation is then sent to the display driver 204, which in turn 20 generates appropriate graphical image data 107 to be output to one or more virtual compass interfaces 108.
The modes of operation of a virtual compass interface 108 will now be described with reference to Figures 3a, 3b, 3c and Figure 4. The graphical image data 107 transmitted 2s to the virtual compass interface 108 is formulated around a virtual three-dimensional domed compass 300, having division markings 302. The virtual three-dimensional domed compass 300 generally has the appearance of a ships conventional domed floating compass with additional overlaid information. The display driver 204 orientates (rotates) the virtual compass 300 according to the present heading of the 30 craft, so that the division marking at the front of the virtual compass 300 indicates the craft's heading thereby emulating a real domed ship's compass. These division markings 302 are overlaid with a coloured (yellow) central vertical marker
304 (commonly referred to as a 'lubber line') to clearly signify the present heading. The heading is also confirmed as a numeric value 306 in the top left-hand corner of the virtual compass interface 108.
s The three-dimensional domed compass 300 is displayed in a manner consistent with a typical view of a real domed compass on a ship. More specifically, the compass 300 is displayed at an acute angle to the plane of rotation such that the user can see the markings 302 on the inside of the compass 300 as well as those on the outside simultaneously. This way of viewing the compass 300 makes it considerably easier for a user to use the navigation system 100 as it operates intuitively, as the user would expect. A series of bearings to be followed can be pre-programmed into the navigation system l s 100 using the button control panel 206. The display driver 204 outputs each bearing, or course to steer (CTS), as a numeric value 308 at bottom centre of the virtual compass interface 108. It also positions an arrow symbol 312 above and pointing to the division marking 302 which corresponds to the numeric bearing value 308. An additional numeric bearing value 310 also appears at the top of the virtual compass interface 108, 20 slightly right of centre, which allows the helmsman or pilot 110 to easily scan and compare it with the numeric heading value 306. The numerical bearing value 310 is distinguishable from the numeric heading value 306 by virtue of the relative sizes and markings used.
2s When a craft is deviating from its course, as a result of a helmsman or pilot 110 not accurately following a pre-programmed bearing, the display driver 204 outputs a series of corrective steering arrows 314, depending on the scale of the inaccuracy, to the virtual compass interface 108 in either the bottom left or right corners. In Figures 3a, 3b and 3c, the pre-programmed bearings are 10 , 17 and 35 , respectively. However, 30 the pilot or helmsman 110, in these examples, resolutely maintains a heading of 0 in order to demonstrate the assistance that is provided by the virtual compass interface
108. The arrows 3t4 are coloured green on the right-hand side of the display to indicate turn to right (Starboard) and red on the left-hand side of the display to indicate turn to left (Port) in line with international maritime conventions. This further assists any user in learning how to operate the navigation system 100, quickly.
In Figure 3a, when the pilot or helmsman 110 is only 10 off the preprogrammed bearing, the display driver 204 causes a single green rightpointing corrective steering arrow 314 to be output by the virtual compass interface 108. In the second example of Figure 3b, when the preprogrammed bearing has changed to 17 and hence the actual lo heading of 0 has further diverged from the intended course, the number of green corrective steering arrows 314 is increased to two. Similarly, in the third example of Figure 3c, three green corrective steering arrows 314 are output when the difference between the pre-programmed bearing and actual heading has increased to 35 .
5 Hence, the number of corrective steering arrows 314 output to the virtual compass interface 108 is indicative of the size of the steering error and alerts the helmsman or pilot 110 to the scale of corrective action required. In addition, the direction in which the corrective steering arrows 314 point and their colour indicates to which side the steering device 112 should be turned to rectify the heading. In summary, the virtual
20 compass interface 108 allows a pilot or helmsman 110 to view and assimilate navigational data quickly and indicates any corrective steering action which should be taken immediately.
The virtual compass interface 108 can also operate in a leeway mode, as shown in 25 Figure 4, which the helmsman or pilot 110 can request using the button control panel 206. Leeway mode provides a graphical measure of the degree to which the course over ground (actual movement direction) of the craft differs from the heading of the craft (direction in which the craft is pointing). In other words it indicates the amount or angle of orientation of the craft relative to its direction of travel. In leeway mode, the 30 display driver 204 applies block shading 402 to the division markings 302 which separate the craft's present heading (indicated by the vertical marker 304) and the
( course over ground (indicated by leftmost shading block 406 in Figure 4) . In this way, the pilot or helmsman can quickly see how far off the bearing the craft is being pushed by the wind, or by currents, for example. In addition, a helmsman 110 on a yacht, say, may realise that because of wind direction, their craft will travel faster if it is directed 5 along a slightly different bearing. The leeway mode allows the helmsman 110 to visually monitor how far off bearing the craft is sailing, for example.
More specifically, Figure 4 shows a course to steer of 35 , a current heading of 0 and a course over ground of 35 . This results in a leeway mode range of 0 to 35 . By its lo very definition, in the Leeway mode the current heading 304 is always within the leeway mode range 400 (it always defines one end of the range), and the other end of the range is defined by the actual course over ground 406. In the example shown in figure 4, the course over ground 406 corresponds to the course to steer (as indicated by marker 312) and so no corrective steering arrows 314 are provided on the display 108.
However, if the course to steer 312 and the course over ground 406 were not equivalent, then the leeway mode range 400 would also indicate this and corrective steering arrows 314 would appear on the display 108.
The practical assistance provided by the virtual compass interface 108 will now be 20 demonstrated, with reference to Figures 5, 6a, 6b and 6c, by way of an example in which a boat is to be guided into harbour. Typically, before approaching a harbour, a helmsman 110 will already have obtained details of the surrounding waters and safe courses to steer from harbour charts or a marine Almanac. Such courses will be punctuated on the water by a series of coloured navigational buoys, indicating where 25 the next bearing should be adopted. A corresponding set of bearings can be programmed into the navigation system 100 using the button control panel 206.
Figure 5 shows a typical river estuary 500, at the top of which is located a harbour moorings area 502. A fairway buoy 506 marks the entrance to the estuary 500 from the 30 sea 504. From this point onwards the boat has to be steered through a bearings course of 30 , 90 , 10 , 100 and 20 with respect to geographic north, until the safe waters of
( the harbour moorings area 502 are reached. Upon reaching the fairway buoy 506, the helmsman 110 uses the button control panel 206 to engage the series of bearings that he or she has previously programmed into the navigation system 100. Figures 6a, 6b and 6c show the helmsman 1 to attempting to follow the initial bearing of 30 until the s first navigational buoy 508 is reached. Figure 6a shows the virtual compass interface 108 for the helmsman 110 steering an initial course of 39 (9 off to Starboard), whilst Figure 6b shows it following corrective steering to port but resulting in an overshoot to 25 (5 off to Port). In Figure 6c the helmsman 110 has finally achieved the correct heading of 30 .
Two different types of navigational buoy 508 are used within the estuary 500, to indicate whether the buoy 508 should be passed on the starboard or port side of the boat. In the example, after the boat passes the first buoy 508 on the boat's starboard side, the helmsman 110 uses the button control panel 206 to switch to the next bearing 5 within the preprogrammed series. At this point the numeric bearing value 308 and the additional numeric bearing value 310 on the virtual compass interface 108 change from 30 to 90 . Using the button control panel 206, the helmsman 110 can program the display driver 204 to output changes to the virtual compass interface 108 either instantaneously or progressively (see second embodiment for more details). The latter 20 mode is advantageous when a large change in direction is required and the arrow symbol 312 on the virtual compass interface 108, which marks the bearing, may otherwise disappear around the back of the dome 300 immediately.
In this way, using the virtual compass interface lO8 and the button control panel 206, 95 the helmsman 110 is able to navigate safely and efficiently to the harbour moorings area 502. The use of the preprogrammed series of bearings is particularly advantageous when control of a boat is handed over to another helmsman during the voyage, particularly if this occurs when a more complex navigational course is to be steered as described above. When assuming control of the boat, the new helmsman I I O 30 can immediately comprehend from the virtual compass interface 108 which bearing should be followed, what the boat's present heading is and whether any corrective
steering action is required. This is not only due to the virtual compass interface 108 being an emulation of a real domed compass, but also because of the overlying steering arrows 312 which indicate to the helmsman 110 exactly which way to turn.
5 As mentioned earlier, in addition to outputting navigational data to one or more virtual compass interfaces 108, the navigation system 100 is also able to calibrate deviation values automatically on an individual heading basis. The processing performed by the microprocessor system 200 shown in Figure 2 will now be described in detail, with reference to Figures 7, 8a and fib.
Figure 7 shows a navigation process 700 that is comprised of two parts, each of which will be described in turn below. The first part 702, on the left-hand side, extracts a craft's heading with respect to geographical north, ready for sending to the display driver 204, which will in turn output it to a virtual compass interface 108. The second 15 part 704, on the right-hand side of the navigation process 700 is concerned with automatic calibration of deviation values. Two different scenarios will be referred to below in demonstrating the navigation process 700 and the respective data sets are displayed in Figures 8a and fib. In the first scenario, the deviation value for the craft's heading as provided by the Fluxgate compass 106 is correct, whilst in the second the JO navigation process 700 detects that the deviation value for that particular heading may need updating.
Inputs from the GPS instrumentation 104 and the 'Lluxgate compass 106 are processed in parallel in the first part 702 of the navigation process 700. The craft's position 25 within the geographic north frame of reference, as detected by the GPS instrumentation 104, is received at step 706, along with a local variation value 707. The variation value 707 is extracted at step 708, whilst the heading 709 with respect to geographic north is extracted at step 710. Meanwhile, input from the Fluxgate compass 106 is received at step 712 and is comprised of the heading 711 as read with respect to the craft's 30 magnetic compass and a deviation value 713 for that heading. The deviation value 713 is obtained from a table of deviations in an earlier processing step, which is not shown.
( The craft's heading 715 with respect to magnetic north is determined at step 714 and is comprised of the reading 711 obtained from the magnetic compass corrected for deviation 713.
5 The data sets of Figures 8a and 8b are respectively comprised of: a heading of 60 and 56 with respect to geographic north; a consistent variation value of 20 ; a consistent heading of 30 with respect to north as indicated on the craft's magnetic compass. In the first scenario the deviation value 713 for a magnetic compass heading of 30 is 10 , whilst in the second scenario it is 6 . Hence, the heading 709 extracted with lo respect to geographic north at step 710 of the navigation process 700 is 60 , whilst the heading 715 with respect to magnetic north which is extracted at step 714 is 40 in the first scenario but 36 in the second scenario.
The variation value 707 extracted at step 708 is added, at step 716, to the magnetic heading 715 obtained in step 714, giving 60 in the first scenario but 56 in the second one. These values 717 are compared at step 718 with the heading 709 obtained from the GPS instrumentation 104 at step 710. In the first scenario, the heading 709 obtained from GPS instrumentation 104 is equal to the heading 717 derived from the Fluxgate compass 106. In this case the navigation process 700 proceeds to step 720, so where the microprocessor system 200 accesses input from the button control panel 206, before the navigation process 700 completes at step 722 by outputting navigation data 107 to the display driver 204.
However, in the second scenario, the GPS heading 709 from step 710 and the heading 25 717 derived from the Fluxgate compass 106 at step 716 are not found to be equal at step 718. In this case the navigation process 700 proceeds to step 724, where the microprocessor system 200 checks whether the navigation system 100 has been set to operate in leeway mode. If leeway mode has been selected, then it is assumed that the magnetic heading 715 obtained from the Fluxgate compass 106 is incorrect. This is 30 because the Fluxgate compass 106 indicates the direction in which the front of the craft is pointing, rather than the direction in which it is moving. For example, in high
winds a sailing boat is likely to be blown sideways. Hence, the microprocessor system 200 proceeds at step 720 to output the heading 709 extracted at step 710 from the GPS instrumentation 104.
s If the navigation system 100 is not operating in leeway mode, then the navigation process 700 proceeds to step 726 where the validity of the data received from the GPS instrumentation 104 is checked. The criteria employed in this regard are the time period over which the heading 709 has been held and the speed at which the craft is travelling. For example, in heavy seas it is unlikely that a heading could be held with lo any accuracy and so a change to the deviation value could not be made with authority.
Similarly, if a craft is travelling too slowly then its position may be deemed to be stationary by the GPS instrumentation 104, as mentioned earlier. In such cases, no update 727 to the table of deviations 730 is made. In contrast, in calm conditions when moving at reasonable speed, there would be a high degree of confidence that any Is difference between the heading 709 derived from the GPS data and the heading 717 derived from the Fluxgate data would be due to a change in the deviation 713 for that heading as compared to the previously stored value. In this case, the navigation process 700 proceeds to step 728, where the deviation value 713 for the present heading is updated with the corrected value and stored in the table of deviations at step 730. So 20 for the second scenario described above, the deviation value 713 would be updated from 6 to 10 . This new value for the heading's deviation is then substituted for the previous value at step 716 of the navigation process 700, which thereafter subsequently proceeds in the same way as for the first scenario.
2s A second embodiment of the present invention is now described with reference to Figure 9. The second embodiment is very similar to the first embodiment in that it uses the same compass but with slight modification in the mode of operation to achieve a significant change of application. Accordingly, to avoid unnecessary repetition, only the differences between the two embodiments will be described hereinafter.
The major difference of the second embodiment over the first is that the second embodiment is designed to be used in 'sport aviation', namely in highly manoeuvrable aircraft as well as in leisure vessels such as boats. In particular, the system has an additional aircraft function called 'turn rate assistance', which is described below.
The turn rate assistance feature is designed to indicate the correct rate of turn to use for procedural' turns or other situations where a specific rate of turn is required.
Procedural turns are required for correct positioning when making approaches to airfields and flying in 'holding patterns' to await permission to approach a location or
lo to continue in a given direction. Typically, a turn rate of 180 per minute is required for these procedural turns in order to exit the turn in the correct location, though any other predetermined rate could be used. Professionally trained pilots are trained to make constant rate turns and exit these turns on a given heading, however, less experienced pilots find making these manoeuvres difficult. The present embodiment 5 displays a combination of a moving course to steer heading indicator 312 and an actual heading in one instrument display. This has been found to dramatically improve accuracy and ease of use in these situations.
Figure 9 shows a typical 'racetrack hold pattern 900. This consists of four, one-minute 20 sections 902, a straight track 904 on a given heading followed by a rate one turn 906 onto the reciprocal of the heading, a second straight track 908 on the reciprocal heading and finally, a second rate one turn 910 back onto the original heading. If the procedure is followed accurately, after four minutes the aircraft is back in the same location as at the start, this is as required for holding.
To fly the holding pattern 900 using the present embodiment, two preset headings are used with the 'turn rate assist' mode indicating the correct headings when on the first and second straight tracks 904, 908. When a pilot reaches the end of the first straight track 904, the arrow symbol 312 showing the course to steer starts to move in relation 30 to the domed compass division markings 302 towards desired course to steer of the second straight track 908. However, the rate at which the arrow symbol 312 moves is
in line with desired rate of 180 per minute. This slow moving arrow symbol 312 can be used by the pilot to steer the craft, at a constant rate, until the required course to steer has been achieved. He does this by simply steering the craft to make the current heading central vertical marker 304 constantly follow the moving arrow symbol 312 5 until it has reached its course to steer heading and has stopped moving. By moving the arrow 312 at a constant rate (180 per minute), the rate of turn between the preset headings also remains constant (assuming the pilot can steer the aircraft to maintain the current heading marker 304 moving constantly with the automatically moving course to steer arrow 312). Results of tests on use of this feature have shown a lo significant improvement in the ability of inexperienced pilots to correctly manoeuvre aircraft in holding patterns, for example.
As has been mentioned above, the first embodiment can also move the arrow symbol 312 progressively in the case of large and rapid changes in course to steer. For sea 5 going leisure craft, the rate of turn is less important as it is difficult to turn fast and with any reasonable accuracy as it depends on many other factors (such as sea currents, wind direction, current speed, etc). However, in principle, the features of the second embodiment can be implemented in the first embodiment resulting in slow predetermined rates of change for sea leisure craft in order to assist in controlled rate 20 of turns.
Whilst it has only been described briefly, the display can be a colour display with different symbols being made more easier to see by virtue of their colour. For example, both the course to steer arrow 312 and the current heading marker 304 can be bold and 2s different colours to everything else on the display to be readily determinable. Also, whilst not described herein, it is to be appreciated that the use of flashing markers and other standard graphical techniques can be employed to draw the user's attention to a given situation being monitored by the display.
30 Having described particular preferred embodiments of the present invention, it is to be appreciated that the embodiments in question are exemplary only and that variations and modifications, such as will occur to those possessed of the appropriate knowledge
( and skills, may be made without departure from the spirit and scope of the invention as set forth in the appended claims. For example, even though graphical symbols have been used in both embodiments, some of these can also be supplemented by audible signals which also alert the user. For example, the corrective steering arrows can be 5 supplemented with a sounder that emits one, two or three beeps to indicate the degree to which the steering needs to be changed together with a different pitch for Starboard or Port. This may be further enhanced by instead having a synthesised human voice instructing the helmsman to change direction by a given degree. For example the synthesised voice could say 'You are slightly off course, please turn to Port by 10 lo degrees' or 'You are significantly off course, please turn to Port by 30 degrees'.

Claims (1)

  1. CLAIMS:
    1. A navigation apparatus for assisting a user in the steering of a craft, the apparatus comprising: s processing means arranged to receive a magnetic compass signal from a magnetic compass indicating the magnetic field direction at a current geographic location and to
    generate navigational data corresponding to the magnetic field direction; and
    display means arranged to generate and display a rotatable image of a compass, to be responsive to the navigational data received from the processing means to orient the lo compass image with respect to a current heading marker on the display, and to display a graphical image showing a pre-programmed course to steer in relation to the compass image such that any difference between the course to steer and the current heading can readily be determined graphically by the use of the apparatus.
    5 2. A navigation apparatus according to Claim I, wherein the display means is
    arranged to display at least one direction symbol indicating, with reference to the current heading marker, the direction to steer the craft in order to reduce any difference between the current heading and the preprogrammed course to steer.
    20 3. A navigation apparatus according to Claim 2, wherein the processing means is arranged to generate a difference signal which indicates the degree of the difference between the current heading and the course to steer, and the display means is arranged to modify the at least one direction symbol in response to receipt of the difference signal such that the degree of difference is graphically indicated to the user.
    4. A navigation apparatus according to Claim 2 or 3, wherein the at least one direction symbol is coloured differently depending on the direction indicated to steer.
    S. A navigation apparatus according to any of Claims 2 to 4, wherein the at least one 30 direction symbol comprises two opposed direction symbols, indicating a left turn and a right turn respectively.
    6. A navigation apparatus according to Claim 5 as dependent on Claim 4, wherein the one direction symbol indicating a left turn is displayed as a red symbol and the direction symbol indicating a right turn is displayed as a green symbol.
    7. A navigation apparatus according to any preceding claim, wherein the display means is arranged to generate and display numerical symbols indicating the current heading. lo 8. A navigation apparatus according to any preceding claim, wherein the display means is arranged to generate and display numerical symbols indicating the pre-
    programmed course to steer.
    9. A navigation apparatus according to Claim 8 as dependent on Claim 7, wherein the 5 numerical symbols indicating the current heading and the pre-programmed course to steer are displayed adjacent each other to assist user comparison.
    10. A navigation apparatus according to any preceding claim, wherein the display means is arranged to generate and display a rotatable threedimensional simulation of a 20 compass.
    11. A navigation apparatus according to Claim 10, wherein the display means is arranged to generate and display the simulation of the compass as viewed from an acute angle to the plane of rotation of the compass.
    12. A navigation apparatus according to any preceding claim, wherein the processing means is arranged to calculate the difference between the course to steer and the current heading and the display means is arranged to remove the course to steer graphical image from the display when the difference is above a predetermined amount.
    13. A navigation apparatus according to any preceding claim, wherein the display
    ( means is arranged to display a zone image placed in relation to the compass image, the zone image indicating the degree of difference between the current heading and an actual course over ground of the craft.
    5 14. A navigation apparatus according to any preceding claim, wherein the processing means is arranged to generate an alarm condition when the difference between the current heading and the course to steer exceeds a predetermined limit, and wherein the alarm condition generates an audible signal from the processing means.
    lo 15. A navigation apparatus according to any preceding claim, wherein the processing means is arranged to receive location information from a position determining system and to use that location information in correcting distortions in the magnetic compass signal.
    16. A navigation apparatus according to Claim 15, wherein the processing means is 5 arranged to receive location information from the Global Position System.
    17. A navigation apparatus according to Claim 16, further comprising instrumentation for deriving the current location using the Global Position System.
    20 18. A navigation apparatus according to any of Claim 15 to 17, wherein the processing means is arranged to calculate the variation of the magnetic compass signal by use of the location information.
    19. A navigation apparatus according to Claim 18, wherein the processing means is 25 arranged to calculate the deviation of the magnetic compass signal by use of a pre-stored table of deviation values for the craft.
    20. A navigation apparatus according to any of Claims 15 to l 9, wherein the processing means is arranged to calculate a position-derived heading of the craft from the current 30 location information received over a given time period.
    ( 21. A navigation apparatus according to Claim 20 as dependent on Claim 19, wherein the processing means is arranged: to receive condition information representative of the geographic conditions under which the magnetic heading information has been received; 5 to compare the positionderived heading with a magnetic-derived heading from the navigational data and, in the event of a difference, to adjust an appropriate deviation value in the table of deviation values to remove the difference, if the condition information validates the magnetic-derived heading information by showing a relatively steady state.
    22. A navigation apparatus according to any preceding claim, further comprising a magnetic compass for generating the magnetic compass signal indicating the magnetic field direction at the current geographic location.
    5 23. A navigation apparatus according to Claim 22, wherein the magnetic compass comprises a Fluxgate compass.
    24. A navigation apparatus according to any preceding claim, further comprising data input means operatively coupled to the processing means, the data input means being 20 arranged to input user-defined course to steer information and/or to configure the mode of operation of the apparatus.
    25. A navigation apparatus according to any preceding claim, wherein the display means is arranged to move the graphical course to steer image at a visibly noticeable rate 2s from an existing course to steer heading to a new course to steer heading.
    26. A navigation apparatus according to Claim 25, wherein the display means is arranged to move the graphical course to steer image at a predetermined visible rate such that the user can steer the craft at the same rate by keeping the current heading of the craft 30 and the course to steer marker in a constant relational position to each other.
    27. A method of assisting a user in the steering of a craft, the method comprising: receiving a magnetic compass signal from a magnetic compass indicating the magnetic field direction at a current geographic location;
    generating navigational data corresponding to the magnetic field direction;
    s generating and displaying a rotatable image of a compass; orienting the compass image with respect to a current heading marker on the display in response to the navigational data; and displaying a graphical image showing a pre-programmed course to steer in relation to the compass image such that any difference between the course to steer and the current lo heading can readily be determined graphically.
    28. An interactive navigation tool for assisting a user in the steering of a craft, the tool being arranged to generate navigational data corresponding to a sensed magnetic field
    direction; and comprising display means arranged to generate and display a rotatable 5 three-dimensional simulation of a compass, the display means being responsive to the navigational data to orient the compass simulation with respect to a current heading marker on the display, and being arranged to display a graphical symbol indicating to the user a direction to steer in order to unify the current heading and a pre- programmed course to steer graphical image generated and displayed on the display means.
    29. A method of assisting a user in the steering of a craft, the method comprising: generating navigational data corresponding to a sensed magnetic field direction;
    generating and displaying a rotatable three-dimensional simulation of a compass; orienting the compass simulation with respect to a displayed current heading 2s marker in response to the navigational data; and displaying a graphical symbol indicating to the user a direction to steer in order to unify the current heading and a pre-programrned course to steer graphical image generated and displayed on the display means.
    30 30. A navigation device for determining a corrected geographic heading for a craft, the .. device composing:
    processing means arranged to receive current location information from a geographic position determining device. magnetic-derived heading information from a magnetic compass device and condition information representative of the physical conditions under which the magnetic heading information has been received; and to 5 generate a position- derived heading of the craft from the current location information received over a given time period; the processing means being further arranged: to correct the magnetic-derived heading information for magnetic deviation by use of a pre-stored table of magnetic deviation values for the craft; and lo to compare the corrected heading information with the position-derived heading and, in the event of a difference, to adjust an appropriate deviation value in the table of deviation values to remove the difference, if the condition information validates the magnetic-derived heading information by showing a relatively steady state.
    5 31. A method of determining a corrected geographic heading for a craft, the method comprising: receiving current location information from a geographic position determining device, magnetic-derived heading information from a magnetic compass device and condition information representative of the conditions under which the magnetic heading 20 information has been received; generating a position-derived heading information of the craft from the current location information received over a given time period; correcting the magnetic-derived heading information for magnetic deviation by use of a pre-stored table of magnetic deviation values for the craft; 25 comparing the corrected direction information with the position-derived heading information; and, in the event of a difference and if the condition information validates the magnetic derived heading information by showing a relatively steady state, updating the table of deviations with a deviation value calculated to remove the 30 difference.
    32. A method according to Claim 31, further comprising determining the magnetic variation of the current location information, and correcting both the position-derived heading information and the corrected magneticderived heading information for magnetic variation.
    33. A method according to Claim 31 or 32, further comprising determining whether a leeway mode of operation has been selected prior to the adjusting step, thereby indicating that there is a difference between the heading and a course over ground of the craft.
    In 34. A method according to any of Claims 31 to 33, wherein the condition information includes speed of the craft over a predetermined time period and/or the period over which the current magnetic-derived heading has been held.
    35. A method according to any of Claims 31 to 34, further comprising outputting the 15 corrected geographic heading for the craft to a graphical display.! 36. A method, navigation device, navigation tool or navigation apparatus substantially as described herein with reference to the accompanying drawings.
GB0221308A 2002-05-02 2002-09-13 Navigational instrumentation and display Withdrawn GB2388195A (en)

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GB0210131A GB0210131D0 (en) 2002-05-02 2002-05-02 Improvements relating to navigational instrumentation
GB0218052A GB0218052D0 (en) 2002-05-02 2002-08-02 Trunor virtual compass device

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Application Number Priority Date Filing Date Title
GB0424058A GB2403297B (en) 2002-05-02 2003-05-01 Improvements relating to navigational instrumentation
PCT/GB2003/001880 WO2003093762A1 (en) 2002-05-02 2003-05-01 Improvements relating to navigational instrumentation
AU2003227900A AU2003227900A1 (en) 2002-05-02 2003-05-01 Improvements relating to navigational instrumentation

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WO2008080103A1 (en) * 2006-12-22 2008-07-03 Johnson Controls Technology Company Compass with ambient light
GB2479456B (en) * 2010-04-09 2016-04-20 Csr Technology Holdings Inc Method and apparatus for calibrating a magnetic sensor

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US5270936A (en) * 1989-09-05 1993-12-14 Pioneer Electronic Corporation Simplified navigation apparatus
US6154703A (en) * 1997-06-20 2000-11-28 Yamaha Hatsudoki Kabushiki Kaisha Control for vehicle navigational system
US6166686A (en) * 1998-10-30 2000-12-26 Northrop Grumman Corporation Corrected magnetic compass

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* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US5270936A (en) * 1989-09-05 1993-12-14 Pioneer Electronic Corporation Simplified navigation apparatus
US6154703A (en) * 1997-06-20 2000-11-28 Yamaha Hatsudoki Kabushiki Kaisha Control for vehicle navigational system
US6166686A (en) * 1998-10-30 2000-12-26 Northrop Grumman Corporation Corrected magnetic compass

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2008080103A1 (en) * 2006-12-22 2008-07-03 Johnson Controls Technology Company Compass with ambient light
GB2479456B (en) * 2010-04-09 2016-04-20 Csr Technology Holdings Inc Method and apparatus for calibrating a magnetic sensor
US10641625B2 (en) 2010-04-09 2020-05-05 CSR Technology Holdings Inc. Method and apparatus for calibrating a magnetic sensor

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