Method and arrangement for representing data in vehicle navigation systems

A method and arrangement for representation of data in a navigation system includes an input unit, a data memory, a position-determining unit, an evaluating unit and a control unit to control a display. From a destination entered in the input unit and the current vehicle location determined by the position-determining unit, the evaluating unit determines a route to the destination from cartographic data stored in the data memory. The evaluating unit also selects reference points of decision and/or orientation along the route and the scale of the map section displayed in the display unit is adjusted as a function of the distance between the current vehicle position and the next point of decision and/or orientation.

BACKGROUND OF THE INVENTION 
This invention relates to method and arrangements for representing data in 
vehicle navigation systems. 
Navigation systems for vehicles are arranged so that map information stored 
in a memory of large capacity, for example a CD-ROM, is indicated and/or 
reproduced on a picture screen. The map information may be displayed, for 
example in the form of routes, i.e. by direction and/or course of travel, 
by means, distances and directions of roads, places along the roads or in 
the form of places and names of intersections and localities, and names of 
buildings. 
The purpose of such navigation systems is to indicate to the vehicle 
operator on the screen, the place where the vehicle is located, the 
vehicle position being indicated in each instance with a map image as a 
background. The indication of the vehicle position with a map image in the 
background may be achieved in several ways. In one display method the 
vehicle indicator is fixed in one position, generally a central position, 
relative to the screen and the background image of the map is shifted 
appropriately as the vehicle travels. 
This method is classified in turn into two submethods: 
(a) The upper direction of the screen is fixed, always oriented, for 
example, to the north. The background map image shifts parallel to the 
direction of a mark or icon representing the vehicle. Although the mark 
remains in one position on the screen, it changes its orientation on the 
screen in accordance with the actual direction of motion or travel of the 
vehicle with respect to the map, and the background map image shifts its 
direction of motion in accordance with the change of orientation of the 
mark. 
(b) The mark does not change its orientation in accordance with a change of 
direction of motion of the vehicle. However, the background image of the 
map moves parallel to the orientation of the mark and thus rotates in 
accordance with the actual motion of the vehicle with respect to the 
ground. 
According to a second basic method, a single image section of the map is 
reproduced in stationary form and the top to the map on the screen is 
fixedly directed to the north. The mark representing the vehicle moves 
over the stationary image of the map until the vehicle reaches a location 
corresponding to a marginal section of the map image on the screen. At 
that time, and successively thereafter, additional, non-shifting sections 
of the map are displayed to show the region in which the vehicle is 
traveling. 
In another navigation system, after entry of a destination, the route from 
the present location to the destination as recommended by the system is 
automatically selected on the screen and indicated on the map. This 
navigation system, indicating a combination of both the route and the 
present vehicle position, in principle displays on the screen only the 
route along which the vehicle is traveling. At best, it will show corners 
at which the vehicle can turn. Therefore, such a navigation system has the 
following disadvantages. In the display on the screen, the length of the 
remaining route shortens as the vehicle position travels along the route. 
Also, the end of the screen may possibly be reached before the vehicle 
arrives as the destination. At that time, the continuation of the route is 
not shown, and the operator is not able to ascertain the present vehicle 
position. If, according to the method described above, the position of the 
vehicle indicator is maintained at the center of the screen, the length of 
the route reproduced in the display amounts to about half the total size 
of the screen. This is disadvantageous in terms in terms of effective use 
of a small or narrow screen. 
U.S. Pat. No. 5,274,387 discloses a navigation system for vehicles with a 
display predetermined size to reproduce a map image having provision for 
setting the scale of the map image and for showing the present vehicle 
position in which, in a first mode, the map image is reproduced to a scale 
and shifted so that the current vehicle position is always shown at about 
the center of the display, whereas, in a second mode, the route of travel 
is indicated at essentially its maximum length on the map image. In the 
second mode, before the commencement of display, a map image is set on the 
display permitting selection of a maximal segment of the route of travel 
for display and thereafter the indicated segment of the travel route is 
traversed at constant map scale so that, after traversal of the displayed 
segment of the travel route, another map image is displayed having the 
same scale and again displaying a maximal segment of the travel route. 
U.S. Pat. No. 5,537,323 discloses a navigation system having a memory for 
storing cartographic data, a vehicle position detector unit, a control 
unit, an input unit, an image memory and a display unit, the control unit 
being arranged to direct a user along a previously determined route on the 
basis of data contained in the vehicle position detector unit and the 
cartographic data. The control unit is also arranged to successively 
reproduce the relevant map sections on the display unit from cartographic 
data stored in the image memory and selected in terms of a current vehicle 
position determined by the position detector unit. The control unit 
includes an image processor for reproducing the previously determined 
route in a complete manner in the map section of the display unit, while 
the image processor represents the route segment traversed to reach the 
current vehicle position in a different manner, reproducing only the local 
surroundings of the current vehicle position, including local 
intersections and route indications on the map. 
German Offenlegungsschrift No. 195 16 647 discloses a navigation system for 
motor vehicles having a data memory and a display supported with 
information from the memory for a map section containing the current 
vehicle location, in which the scale of the map section is automatically 
enlarged at a low vehicle section. The automatic enlargement of the scale 
saves trouble for the operator. Moreover, coupling of the map scale with 
the vehicle speed assures that the operator actually receives the map 
section and scale he requires in terms of his style of driving. At high 
speed, as for example on a motorway, the map is reproduced at a small 
scale and contains information about a comparatively large area. 
Typically, a small scale of 1:100,000 may be used in this case. At low 
speeds, however, such as occur in city traffic, the map scale is enlarged 
to a scale of 1:10,000 for example. Also, an intermediate scale of 
1:50,000, for example, may be provided when the vehicle is at an 
intermediate speed. The assignment of a scale to the current vehicle speed 
may reasonably be made according to an average value of the vehicle speed. 
For example, the average vehicle speed may be taken over a period of 10 
minutes. In addition, according to this reference the change of scale may 
also be made dependent on the distance of the vehicle from its 
destination. 
A destination in turn may, for example, be entered before the beginning of 
the trip or else entered for a selected trip distance. For example, if the 
vehicle is at a distance of 1 kilometer from its destination, a switch to 
the larger scale may be made automatically. This facilitates convenient 
finding of the destination. A disadvantage of such navigation systems is 
that the required density of information does not automatically depend on 
the vehicle speed, so that the vehicle operator may receive too much or 
too little information at the scale shown. 
SUMMARY OF THE INVENTION 
Accordingly, it is an object of the present invention to provide a method 
and arrangement for representing data in vehicle navigation systems which 
overcomes disadvantages of the prior art. 
Another object of the invention is to provide a method and arrangement for 
representing data in vehicle navigation systems in which the 
representation of the data is optimally adapted to the needs of the 
vehicle operator. 
These and other objects of the invention are attached by providing a 
navigation system in which the scale of a displayed map is adjusted in 
accordance with the distance of the vehicle from a predetermined location 
on the route to be followed by the vehicle. By adaptive adjustment of the 
scale as a function of the distance between the current vehicle location 
and the nearest point of decision and/or orientation, the vehicle operator 
is provided with a high-density of information in accordance with the map 
scale whenever orientation is really required. This may be the case even 
at high vehicle speeds, for example when approaching a selected highway 
exit in which case a small map scale would be indicated based on the 
vehicle speed. By contrast, according to the invention the driver always 
gets an enlarged scale, independently of his vehicle speed, when 
approaching the preselected locations on the route which are points of 
decision and/or orientation, so that the operator receives the maximum 
amount of data from the display just when he has to make a decision, for 
example because a curve or other steering maneuver is required. After the 
operator has passed the point of decision, the scale is reduced again, so 
that the driver again receives an improved overview without unnecessary 
details. 
In a particular embodiment of the invention, the scale is chosen so that 
the current location and the nearest point of decision for the driver will 
just be pictured at the edges of the display and the route between those 
points fills the display screen as completely as possible. 
Further, provision is made so that the operator can select additional 
points of orientation and/or remove selected points of orientation, thus 
making an individually adapted display possible. Thus, for example, the 
operator may be quite familiar with one segment of the route so that he 
may find large-scale representation superfluous or even annoying. On the 
other hand, there may be segments of the route that the operator finds 
especially troublesome so that additional information would be helpful. 
In addition, the rate of adaptation, for example the frequency with which a 
new representation is displayed, may be made dependent on the vehicle 
speed. 
Also, the extent of adjustment of scale when approaching a decision point 
may be different from the extent of adjustment after passing the point of 
decision.

DESCRIPTION OF PREFERRED EMBODIMENTS 
In the typical embodiment illustrated in the drawing, a data representation 
arrangement 1 includes a data input 2, a vehicle position-determining unit 
3, an evaluating unit 4, a data memory 5, a control unit 6 and a display 
7. 
The data input unit 2, which may, for example, be an alphanumeric key pad, 
has its output connected to a data input of an evaluating unit 4. 
Similarly, a vehicle position-determining unit 3 has an output connected 
to another data input of the evaluating unit 4. A desired destination can 
be entered by the vehicle operator into the input unit 2. The evaluating 
unit 4 then determines, by using conventional algorithms, an optimal route 
between the current vehicle location and the desired destination based on 
cartographic data stored in the data memory 5 which are drawn upon to 
provide, for example, a display in the form of a digital vector chart. If 
desired, current traffic reports are taken into account in setting up the 
route. 
After the route has been determined, it is provided to the operator on the 
display unit 7. In addition, the evaluating unit 4 selects points of 
decision and orientation and highlights them visually on the route 
displayed. Such points of decision may be places where the operator must 
perform active maneuvers, for example turns at intersections, motorway 
exits and the like. Points of orientation are places of high density of 
traffic information, where the driver need not necessarily take any 
action, but might be misled into taking action for lack of specific 
information. The driver may then confirm the route with the selected 
points of decision and orientation as shown in the display 7 or else put 
in additional points of orientation and/or remove selected points. 
When this input operation has been concluded, the evaluating unit 4 
contains the complete route with a selected number of points of decision 
and orientation. The evaluating unit 4 then reads out the cartographic 
data for the first route segment between the current vehicle location and 
the first point of decision or orientation from the data memory 5 and 
converts them to a scale selected so that the route between the current 
location and the next point of decision or orientation fills the image in 
the display 7 as completely as possible. The next point of decision does 
not necessarily mean the nearest point on a bee line, but the point to be 
passed next in time. 
It is also possible that the current vehicle location may always be 
represented in the center of the display 7. While this reduces the density 
of data to be represented, since a scale about half as large, e.g., 
1:100,000 rather than 1:50,000, must be selected, yet the central vehicle 
representation may improve the operator's visual perception. 
Since the motor vehicle is in motion, a specific representation in the 
display 7 is always correct for only a certain period of time. The 
frequency with which the representation in the display 7 must be updated 
may be either fixed or else variable as a function of external parameters 
such as vehicle speed and/or traffic density. 
As the motor vehicle approaches a point of orientation or decision, the 
data are represented in the display to a larger and larger scale so that 
the operator receives an optimal overview just before that point is 
reached. After the decision or orientation point has been passed, there 
are two alternative procedures. Either the point passed continues to be 
represented for a brief period, in which case the scale will be 
progressively reduced, or the system is switched at once to display the 
next point of orientation or decision so that the route between the 
current vehicle location and that point is made to fill the screen. 
Although the invention has been described herein with reference to specific 
embodiments, many modifications and variations therein will readily occur 
to those skilled in the art. Accordingly, all such variations and 
modifications are included within the intended scope of the invention.