Electronic magnetic compass system and method for interpreting directions of a vehicle

A method and apparatus for interpreting magnetic directions for an electronic compass system mounted on a moving vehicle such as an automobile. The directions of North, Northeast, East, Southeast, South, Southwest, West and Northwest are each assigned predetermined degree ranges which are included in a look-up table used by a controller. The predetermined degree ranges associated with the directions of North, South, East and West are further each set at equal values, while the predetermined degree ranges of Northeast, Northwest, Southeast and Southwest are set equally at a value that is less than the values of the North, South, East and West directions. A flux-gate senses the Earth's magnetic field and generates an analog signal in accordance therewith. The analog signal is converted into a corresponding digital signal by an analog-to-digital converter. The controller receives the corresponding digital signal and converts the digital signal into a degree heading. The controller then compares the degree heading with the eight predetermined degree ranges included in the look-up table and generates a directional heading signal in accordance with the predetermined degree range within which the degree heading falls. A directional heading signal is then output to a visual display and displayed as one of the eight directional headings associated with the eight predetermined degree ranges. The invention thus simplifies the interpretation of heading information generated by an electronic compass system and reduces the chance of driver confusion by interpreting heading information more in accordance with the major geographic directions of North, South, East and West.

CROSS-REFERENCE TO RELATED APPLICATIONS 
The present application is related to the following, co-pending 
applications filed concurrently herewith: 
"Scaling System And Method For An Electronic Compass", application Ser. No. 
07/815,347; 
"Shifting System And Method For An Electronic Compass System", application 
Ser. No. 07/815,267; 
"Data Processing Method For An Electronic Compass System", application Ser. 
No. 07/815,266; 
"Heading Computation For An Electronic Compass", application Ser. No. 
07/815,346; 
"Magnetic Transient Detection And Calibration Technique For An 
Auto-Calibrating Compass", application Ser. No. 07/815,268; 
"Method For Selecting Calibration Data For An Auto-Calibrating Compass", 
application Ser. No. 07/815,264; 
"Flux-Gate Sensor Orientation Method", application Ser. No. 07/815,264; 
"Noise Removal Method For An Electronic Compass", application Ser. No. 
07/815,269; 
"Flux-Gate Sensor Mounting And Method", application Ser. No. 07/815,270. 
The disclosures of all the applications cited above are hereby incorporated 
by reference and made a part hereof the same as if fully set forth herein. 
BACKGROUND OF THE INVENTION 
1. Technical Field 
The present invention relates to electronic compass systems and methods of 
operation therefor, and more particularly to a system and method for 
interpreting degree headings sensed by an electronic compass system in 
accordance with a plurality of predetermined degree ranges and displaying 
directional headings in accordance with the predetermined degree ranges. 
2. Discussion 
The present invention is related to and is an improvement of U.S. Pat. No. 
4,622,843 to Hormel issued Nov. 18, 1986 entitled "Simplified Calibration 
Technique and Auto Ranging Circuit for an Electronic Compass Control 
Circuit". The present invention is also related to U.S. Pat. No. 4,807,462 
issued Feb. 28, 1989, to Rafi A. Al-Attar and entitled "Method for 
Performing Automatic Calibrations in an Electronic Compass." These patents 
are hereby incorporated by reference. The present invention is related to 
and combinable with the commonly assigned patent application "Shifting 
System and Method for an Electronic Compass," application Ser. No. 
07/815,267. This application is hereby incorporated by reference. 
Normally, electronic compass systems employ a magnetic flux-gate sensor. 
The operation of the flux-gate sensor is well documented. See, Hisatsugu 
Itoh, "Magnetic Field Sensor and Its Application to Automobiles", SAE 
Paper No. 800123, pages 83-90, February, 1980; and Doug Garner, "A 
Magnetic Heading Reference for the Electro/Fluidic Autopilot," Sport 
Aviation, Part I, pages 19-26, November, 1981 and Part II, pages 20-32, 
51, December, 1981. These documents are hereby incorporated by reference. 
When an electronic compass system incorporating a flux-gate sensor is 
mounted to a vehicle, such as an automobile, it senses the earth's 
magnetic field as the vehicle travels, and also as the vehicle changes 
direction, and generates an output signal indicative of the heading of the 
vehicle. Typically, the heading is classified into one of eight headings 
corresponding to the geographic directions of North, Northeast, East, 
Southeast, South, Southwest, West and Northwest. Each geographic direction 
further typically comprises an equal range of 45 degrees. For example, the 
geographic North direction might typically be centered at 0.degree. on a 
compass rose, and would typically cover a range of about 337.5.degree. to 
22.5.degree., or about .+-.22.5.degree. from the 0.degree. (due North) 
heading of the compass rose. Thus, the eight geographic directions 
typically are divided into perfectly equal ranges. 
The above-mentioned division of the eight geographic directions into equal 
degree ranges is acceptable for some applications, such as marine 
navigation, where the vehicle, in such case a boat, is typically not 
confined to predetermined paths of travel such as roads. However, with 
motor vehicles such as automobiles, paths of travel are confined to roads, 
which in turn are most often laid out in accordance with the four major 
directional headings of North, South, East and West, or variations of 
these four directions. Roads that are marked and referred to as 
North-South or East-West running roads often include portions which vary 
from the markings of the road. For example, a North-South running road 
marked as "North" may meander at various points to become a slightly 
Northeast or Northwest heading road. 
In situations such as described above, drivers of such vehicles can become 
confused when traveling on a "Northbound" road when an electronic compass 
system mounted on the driver's vehicle is indicating that the vehicle is 
traveling in a Northeast or Northwest direction. Since many, if not most 
North-South and East-West roads meander slightly from their overall 
directions at certain points, the chance for driver confusion can be 
significant. This problem can be particularly troubling when navigating 
freeways running through congested urban areas where such freeways, while 
traveling North-South or East-West overall, often meander considerably 
from their marked directions at various points. 
Accordingly, it is a principal object of the present invention to provide 
an electronic compass system and method for interpreting degree heading 
signals from the system in a manner to help eliminate the confusion that 
exists when temporary variations are encountered in traveling primarily 
North-South and East-West roads, which are marked only as "North", 
"South", "East" or "West". 
It is still a further object of the present invention to provide an 
electronic compass system and method of operation therefor which includes 
a controller and a look-up table, the look-up table having a plurality of 
predetermined degree ranges corresponding to the geographic directions of 
North, Northeast, East, Southeast, South, Southwest, West and Northwest, 
and wherein each of the predetermined degree ranges is uniquely associated 
with one of the just-mentioned geographic directions and wherein degree 
ranges of the major geographic directions of North, South, East and West 
are increased at the expense of the minor geographic directions of 
Northwest, Northeast, Southeast and Southwest. 
SUMMARY OF THE INVENTION 
The above and other objects are accomplished by an electronic compass 
system implementing a preferred method in accordance with the present 
invention. The electronic compass system for implementing the method of 
the present invention is typically mounted on a vehicle, such as an 
automobile, and typically includes the following elements: a sensor for 
sensing the earth's magnetic field and generating a degree heading signal 
representative of a geographic direction in which the vehicle is heading; 
a controller; and a look-up table. The look-up table incorporates a 
plurality of predetermined degree ranges, with each range being uniquely 
associated with one of the eight geographic directions of North, 
Northeast, East, Southeast, South, Southwest, West and Northwest. The 
predetermined degree range (in degrees) of each of the major geographic 
directions of North, South, East and West are further increased at the 
expense of the minor geographic directions of Northwest, Northeast, 
Southwest and Southeast. 
The controller is responsive to the sensor and compares the directional 
heading signal with the predetermined degree ranges of the look-up table. 
The controller then generates a heading signal in accordance with the 
geographic direction of the predetermined degree range within which the 
directional heading signal falls. The signal may then be displayed on an 
external display system to provide a driver of the vehicle a visual 
indication of the heading of the vehicle at any given time. 
In an alternative preferred method of the present invention the 
predetermined degree ranges are varied slightly to provide varying degree 
ranges for each of the geographic directions of North, Northeast, East, 
Southeast, South, Southwest, West and Northwest.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Turning now to FIG. 1, there is shown a block diagram of the electronic 
compass system 10 of the '843 patent to Hormel. Initially, it should be 
understood that the electronic compass system of FIG. 1 and the electronic 
compass systems of FIGS. 4 and 6 are being provided merely as background 
information to illustrate electronic compass systems which may be used to 
implement the preferred methods of the present invention, and that the 
preferred methods of the present invention will be described in detail 
following the discussion of FIGS. 1-6. It should be appreciated that 
virtually any compass system capable of generating heading information in 
the form of degrees could be used to implement the method of the present 
invention. Accordingly, a flux-gate sensor may not be required if an 
alternative, comparable, magnetic sensing device is incorporated. For 
example, "Hall-effect" sensors could be used if so desired. 
The heart of the system of FIG. 1 is a microcomputer 12 which employs an 
8-bit analog-to-digital converter 14. The microcomputer 12 controls 
operation of the electronic compass system 10, beginning with a flux-gate 
driver 16. Upon receipt of a square-wave signal from the microcomputer 12, 
the flux-gate driver 16 adds enough drive to the signal to saturate a 
flux-gate 18. The operation of the flux-gate driver 16 and flux-gate 18 
are explained in the documents incorporated by reference, namely "A 
Magnetic Heading Reference for the Electro/Fluidic Autopilot" and 
"Magnetic Field Sensor and its Application to Automobiles, (SAE Paper No. 
800123)". The flux-gate 18 employs two sense coils oriented 
perpendicularly to one another. Voltages are induced across the sensor 
coils by the presence of the magnetic fields of the vehicle and the earth. 
The voltages from the sense coils of the flux-gate 18 are selected by a 
multiplexer 20. The multiplexer 20 is in communication with the 
microcomputer 12, which generates a signal for controlling a network for 
switching use of a four-pole bandpass filter 22, a synchronous detector 24 
and an integrator 26 periodically from one sense coil to the other. The 
multiplexer 20 is in communication with the four-pole bandpass filter 22, 
which filters out all but the second harmonic signals, whose amplitude is 
proportional to the earth's magnetic field. Second harmonic signals are 
presented to the synchronous detector 24. The function of the synchronous 
detector 24 is to select the portion of the filtered signals to be 
integrated by the integrator 26. The output of the synchronous detector 24 
is a half-wave rectified signal which is fed into the integrator 26. 
The output of the integrator 26 periodically switches back and forth 
between two DC levels corresponding to the two sense coils of the 
flux-gate 18. Integrator output is stabilized by feeding back a current 
through resistor R.sub.f to the sense coils of the flux-gate 18. The 
feedback current eventually generates an equal and opposite magnetic field 
versus that produced by the magnetic field sensed by the flux-gate 18. 
Therefore, the output voltages, V.sub.ox and V.sub.oy, of the integrator 
26 are directly proportional to the sensed magnetic field by a constant 
R.sub.f which is the feedback resistance: 
EQU V.sub.ox =KR.sub.f (V.sub.mx +R.sub.mx). 
where V.sub.mx +R.sub.mx is the geometric addition (or resultant) of the 
magnetic fields of the earth and the vehicle in the x coil. Similarly, 
EQU V.sub.oy =KR.sub.f (V.sub.my +R.sub.my) 
where V.sub.my +R.sub.my is the geometric resultant at the magnetic field, 
of the earth and vehicle in the y coil. 
The ranging circuit 28 used in the '843 patent to Hormel moves the DC 
levels at the integrator output closer to the origin and toward a 
magnitude within the window. The ranging circuit 28 generates a 
compensation field such that 
EQU V.sub.n +R=V+R+V.sub.c or V.sub.n =V+V.sub.c 
where V.sub.n is the new vehicle magnetic field voltage vector, R is 
earth's magnetic field voltage, and V.sub.c is the compensation field 
voltage vector. 
Heading information is determined from the output of the integrator 26. The 
microcomputer 12 is coupled to the integrator output through the 8-bit 
analog-to-digital converter 14. The 8-bit analog-to-digital converter 14 
converts the DC levels to digital codes (i.e., coordinates) referenced to 
a cartesian coordinate system. The microcomputer 12 divides the 
y-coordinate, corresponding to the DC level from one coil, by the 
x-coordinate, corresponding to the other coil, and takes the arctangent of 
the quotient using a piece-wise-linear-function-of-x routine to yield the 
vehicle's heading. Calibration is then performed under the method of the 
'462 patent. 
The integrator 26 employs operational amplifiers which have linear voltage 
output ranges of approximately 0 to V.sub.a volts. In the '843 patent to 
Hormel, the linear voltage output range is approximately 0 to 10 volts. 
Since the voltages induced across the sense coils of the flux-gate 18 may 
be negative or very large, these voltages must be modified for use in the 
integrator 26. Negative voltages are modified by tying the sense coils of 
the flux-gate 18 to a reference voltage of V.sub.cc, halfway between 0 and 
V.sub.a volts. In the '843 patent to Hormel, V.sub.cc is equal to 5 volts. 
The magnitude of the voltage outputs of the integrator 26 are indirectly 
reduced to some extent by the operation of a ranging circuit 28. However, 
the primary purpose of the ranging circuit 28 is to bring the DC output 
levels of the integrator 26 into a range that the software in the 
microcomputer 12 can handle, not to compensate for abnormally large 
vehicle magnetic fields. It accomplishes this through the use of negative 
feedback through resistor R.sub.f. The ranging circuit 28 monitors 
integrator output and employs a variable voltage source, having an 
operational amplifier, to produce feedback. The outputs of the integrator 
26 and ranging circuit 28 are combined in a summing amplifier 30. 
Turning now to FIG. 2, there is shown a voltage window 30. The x and y axes 
correspond to the two DC output levels V.sub.ox and V.sub.oy of the 
integrator 26. The limits of the window 30 are determined by the output 
voltage range of the operational amplifiers within the integrator 26. This 
range is depicted as approximately 0 to V.sub.a volts. The voltage 
V.sub.cc is applied to the junction of the two sense coils and the 
integrator 26 and marks a reference for the origin 0 of the vehicle's 
magnetic field voltage vector V. 
Also shown is the earth's magnetic field voltage vector R and circle 32. 
The earth's magnetic field circle 32 is the locus of points described by 
the earth's magnetic field voltage vector R as the vehicle changes 
heading. The vehicle's magnetic field voltage vector V remains stationary 
with respect to the x and y axes, which are the frame of reference of the 
vehicle (and the flux-gate 18). 
In FIGS. 3a and 3b, there is shown the window 30 of FIG. 2. However, the 
earth's magnetic field circle 32 has been brought partially into the 
window 30 by the operation of the ranging circuit 28 of the electronic 
compass of FIG. 1. The compensation voltage vector V.sub.c is added to the 
vehicle's magnetic field voltage vector V to produce a new vehicle 
magnetic field voltage vector V.sub.n. The earth's magnetic field voltage 
vector R remains the same as before compensation. 
The ranging circuit 28 in FIG. 1 is incapable of producing enough feedback 
current to bring the earth's magnetic field circle 32 totally within the 
window 30. When abnormally large vehicle magnetic fields are present, part 
of the earth's field circle 32 remains outside the voltage window 30 after 
compensation. For vehicle headings in which the earth's magnetic field 
voltage vector R crosses the boundaries of the window 30, the 
microcomputer 12 is incapable of generating accurate headings. If the 
earth's magnetic field circle 32 were totally outside the window 30 after 
compensation, then the microcomputer 12 would be incapable of generating 
any accurate headings, because the operational amplifiers of the 
integrator 26 would be in constant saturation. Thus, calibration under the 
method of the '462 patent would be difficult. 
Turning now to FIG. 4, there is shown the improved electronic compass 
system 34 for implementing the method of the present invention. The system 
34 changes the DC output levels by changing the amount of feedback 
resistance R.sub.f, thereby bringing the voltage across the sense coils to 
within the output voltage range of the integrator 26. This resistance is 
made variable to accommodate variations in magnetic fields among vehicles. 
It may be preset when the electronic compass system is installed in a 
vehicle and would be accessible to service personnel if a particular 
vehicle's magnetic field were to later change. 
As shown in FIG. 5, feedback resistance R.sub.f produces a scaling effect. 
As the feedback resistance R.sub.f increases, the DC output levels of 
integrator 26 increase. Reducing feedback resistance R.sub.f also reduces 
the magnitudes of both the vehicle's magnetic field voltage vector V and 
the earth's magnetic field voltage vector R at the output of the 
integrator 26. The decrease in feedback resistance R.sub.f brings the 
entire earth's field circle 32 within the window of the integrator 26. 
Advantageously, vectors, V and R can be scaled up or down by a factor 
.alpha. that is proportional to feedback resistance R.sub.f. For a fixed 
value of R.sub.f, 
EQU V.sub.ox =KR.sub.f (V.sub.mx +R.sub.mx) (1) 
EQU V.sub.oy =KR.sub.f (V.sub.my +R.sub.my) (2) 
Under the method of the present invention, 
EQU V.sub.ox new =K.alpha.R.sub.f (V.sub.mx +R.sub.mx) 
EQU V.sub.oy new =K.alpha.R.sub.f (V.sub.my +R.sub.my 
or 
EQU V.sub.ox new =.alpha.V.sub.ox 
EQU V.sub.oy new =.alpha.V.sub.oy 
Therefore, V+R will become .alpha.V+.alpha.R after changing the feedback 
resistance R.sub.f by a factor .alpha.. In FIG. 5, the factor .alpha. is 
less than 1 and the vectors V and R are scaled down. 
Since a decrease in feedback resistance R.sub.f reduces the effects of both 
the earth's magnetic field voltage vector R and the vehicle's magnetic 
field voltage vector V, the DC output levels of the integrator 26 are 
incapable of being accurately resolved by the 8-bit analog-to-digital 
converter 14. Therefore, the system of FIG. 4 employs a 10-bit 
analog-to-digital converter 38. Of course, other analog-to-digital 
converters of greater resolving power are also envisioned by this system. 
A commercially available 10-bit analog-to-digital converter is the Model 
No. 68HC68A2 manufactured by RCA. Advantageously, the present invention 
makes calibration under the method of the '462 patent possible for 
abnormally large vehicle magnetic fields. 
Except for the feedback resistance R.sub.f and the analog-to-digital 
converter 14, the elements of the compass system 10 of FIG. 1 are 
identical with those of the compass system 34 of FIG. 4. However, as shown 
in FIG. 6, the system there is not limited to vehicles and is also 
envisioned for use in unmultiplexed electronic compasses employing 
separate feedback resistances and paths, one for each coil. The sensed 
magnetic field in each coil may be processed separately, using bandpass 
filters 42 and 43, synchronous detectors 44 and 45, integrators 46 and 47, 
ranging circuits 48 and 49, feedback resistances R.sub.fx and R.sub.fy, 
and summing amplifiers 50 and 51. 
With reference now to FIG. 7, there is shown a compass rose 60 illustrating 
how the various geographic directions may be segmented in accordance with 
a preferred method of the present invention. Each of the eight geographic 
directions of North, Northeast, East, Southeast, South, Southwest, West 
and Northwest are assigned a predetermined degree range, as indicated by 
reference numerals 62-76. Each of the geographic directions corresponding 
to the major geographic directions of North, South, East and West include 
equal degree ranges 62, 66, 70, 74 which are slightly larger, that is by 
1.degree., than their bordering directions (i.e., the minor geographic 
directions of Northeast, Southeast, Southwest and Northwest, 64, 68, 72, 
76). As shown in FIG. 7, each of the major geographic directions are 
assigned degree ranges of 46.degree., while each of the minor geographic 
directions are assigned degree ranges of 44.degree.. 
It is a principal advantage of the method of the present invention that the 
degree ranges 62, 66, 70, 74 of each of the major geographic directions 
(North, South, East and West) be greater than each of the minor geographic 
directions 64, 68, 72, 76 (Northeast, Southeast, Southwest and Northwest). 
By increasing the degree ranges of the four major geographic directions 
62, 66, 70, 74 as shown in FIG. 7, an electronic compass system such as 
that shown in FIG. 4 interprets sensed geographic directional heading 
information more in accordance with the major geographic directions of 
North, South, East and West. 
Prior art methods of interpreting sensed geographic directional heading 
information have typically included segmenting each of the directions of 
North, Northeast, East, Southeast, South, Southwest, West and Northwest in 
accordance with equal predetermined degree ranges of 45.degree. each. By 
increasing the degree range of the major geographic directions of North, 
South, East and West, an electronic compass system mounted on a vehicle 
provides directional information to the driver of the vehicle more closely 
in accordance with the major geographic directions of North, South, East 
and West. 
The above-described method of assigning the major geographic directions 
greater predetermined degree ranges than the minor directions provides a 
significant advantage to drivers of vehicles when driving on unfamiliar 
roads which temporarily meander in directions out of accordance with the 
overall direction of the road. For example, many roads which are marked 
North and South, and particularly freeways in congested urban areas, 
frequently do not run in North-South directions along their entire 
distance. Such roads often assume, temporarily, Northeast-Southwest 
running headings or Northwest-Southeast headings. Thus, a driver of a 
vehicle driving along an unfamiliar stretch of road which is marked, for 
example, as a North-South road may become confused when an electronic 
compass associated with the vehicle indicates that the vehicle is heading, 
for example, Northeast rather than North as believed by the driver. By 
increasing the predetermined degree ranges of the four major geographic 
directions at the expense of the minor geographic directions, an 
electronic compass system can be programmed to interpret minor deviations 
from the four major geographic directions as still being in accordance 
with the major geographic directions. Put differently, the electronic 
compass system can be programmed to "ignore" small variations in headings 
from each of the four major geographic directions. Accordingly, even 
though a vehicle traveling down, for example, a North-South road 
temporarily assumes a slight Northeast heading, which would normally cause 
prior art compass systems to generate a Northeast heading signal and 
thereby possibly confuse the driver of the vehicle, the method of the 
present invention would cause the electronic compass system to interpret 
the slightly Northeast sensed direction as still being North and generate 
a North heading signal for the driver. 
In FIG. 8, a compass rose 80 having predetermined degree ranges 82-96 for 
each of the geographic directions North, Northeast, East, Southeast, 
South, Southwest, West and Northwest is shown in accordance with an 
alternative method of the present invention. With this method, the degree 
ranges 82, 86, 90, 94 of major geographic directions of North, South, East 
and West are each increased by 44.degree. (i.e., to 89.degree.) at the 
expense of the minor geographic directions of North, East, Southeast, 
Southwest and Northwest (set to 1.degree.). Thus, an electronic compass 
system sensing the heading of a vehicle will be even less prone to 
interpret temporary, severe heading changes into the Northeast, Southeast, 
Southwest and Northwest directions as a change in heading and will still 
indicate to a driver of the vehicle that the vehicle is heading either 
North, South, east or West. 
While only two different sets of predetermined degree ranges 62-76 and 
82-96 have been illustrated, it should be appreciated that the degree 
ranges associated with the major geographic directions may be set at an 
infinite number of immediate ranges between 45.degree. and 90.degree.. 
Only two differing predetermined degree ranges (i.e., ranges of 46.degree. 
and 89.degree.) have been shown to illustrate the large magnitude by which 
the ranges may vary. It should be appreciated, however, that as the 
predetermined degree ranges are increased at the expense of the minor 
geographic directions the accuracy of the heading information displayed by 
the compass system will appear to decrease relative to the heading 
information which would otherwise be displayed by a convention 8-point 
compass system incorporating eight evenly divided geographic sectors. 
Referring now to FIG. 9, there is shown a program 100 for implementing the 
method of the present invention. Initially, an electronic compass system 
mounted on a vehicle senses the Earth's magnetic direction and feeds an 
analog signal in accordance therewith into an analog-to-digital converter 
of the system, as indicated at 102. The analog-to-digital converter feeds 
a corresponding digital signal into a microcomputer or controller of the 
compass system, as indicated at 104. The controller then converts the 
digital signals received from the analog-to-digital converter into heading 
degrees from 0.degree. to 359.degree., as indicated at 106. 
The controller then takes the converted heading degree values and reads a 
look-up table incorporating the predetermined degree ranges 62-76 of FIG. 
7, as indicated at 108. The heading degree value is then compared against 
the predetermined degree ranges 62-76, as shown in block 108. The 
controller then determines the predetermined degree range 62-76 or 82-96 
within which the heading degree value obtained falls within, and sends a 
heading signal to a display where the signal is displayed as North, 
Northeast, East, Southeast, South, Southwest, West or Northwest, as 
indicated at 110. An example, the values of the predetermined degrees 
ranges 62-76, which should be understood to be exemplary, are illustrated 
in Table 1 below: 
TABLE 1 
______________________________________ 
GEOGRAPHIC PREDETERMINED 
REFERENCE DIRECTIONAL DEGREE 
NUMERAL HEADING RANGE 
______________________________________ 
62 North 337.degree.&lt;-.ltoreq.23.degree. 
64 Northeast 23.degree.&lt;-.ltoreq.67.degree. 
66 East 67.degree.&lt;-.ltoreq.113.degree. 
68 Southeast 113.degree.&lt;-.ltoreq.157.degree. 
70 South 157.degree.&lt;-.ltoreq.203.degree. 
72 Southwest 203.degree.&lt;-.ltoreq.247.degree. 
74 West 247.degree.&lt;-.ltoreq.293.degree. 
76 Northwest 293.degree.&lt;-.ltoreq.337.degree. 
______________________________________ 
It should thus be appreciated that the method of segmenting the various 
geographic directions as disclosed herein serves to significantly reduce 
driver confusion when navigating roads which run primarily North and South 
or East and West, and which temporarily meander into Northeast and 
Southwest or Northwest and Southeast directions. Thus, drivers of such 
vehicles are much less likely to be confused as an electronic compass 
system of the vehicle is preprogrammed to ignore small variations from the 
major geographic directions of North, East, South and West. 
Although the invention has been described with particular reference to 
certain preferred embodiments thereof, variations and modifications can be 
effected within the spirit and scope of the following claims.