DE102016011600A1 - Method for measuring distance - Google Patents

Abstract

A method of measuring the length of a leg with the steps of: a) measuring coordinates of a starting point of the leg; b) measuring coordinates of an endpoint of the leg; c) calculating the Cartesian distance between starting point and end point; d) estimating the variance of the coordinates of at least one of the two points; e) decreasing the Cartesian distance by a positive value increasing with the variance to obtain the length of the leg.

Description

The present invention relates to a method for measuring the length of a route.

With the help of navigation satellites and a navigation device evaluating the signals from these satellites, it is possible at any point on the earth's surface within fractions of a second to measure the longitude and latitude coordinates of the point with an accuracy of a few meters or better.

In principle, the length of a path traveled between two points can be estimated with the aid of such coordinate measurements. The greater the distance between the points, the less the uncertainty in the measurement of their coordinates affects the result, but the greater the error that results from the fact that the distance actually traveled between the points is generally not straightforward. The result of such an estimate is thus systematically smaller than the actual distance covered.

In order to reduce this systematic error, one can divide the distance to be measured into a plurality of sections, measure the coordinates of the start and end points for each section, calculate therefrom the length of each section and add up the obtained lengths. The finer the subdivision into subsections, the more likely the result is systematically too large, since due to the inaccuracy of the coordinate measurements, the path between the measuring points appears more curved than it actually is.

Out DE 10 2014 211 164 A1 is an odometry navigation system is known in which the measurement accuracy is to be improved by merging with various additional sensors.

An object of the invention is to provide a method that allows accurate path measurement based on coordinate measurements of individual waypoints.

• a) Messen von Koordinaten eines Anfangspunkts einer Strecke, im Folgenden als Teilstrecke bezeichnet;
• b) Messen von Koordinaten eines Endpunkts der Teilstrecke;
• c) Berechnen des kartesischen Abstands zwischen Anfangspunkt und Endpunkt;
• d) Abschätzen der Varianz der Koordinaten wenigstens eines der beiden Punkte,
• e) Vermindern des kartesischen Abstands um einen mit der Varianz zunehmenden positiven Wert, um die Länge der Teilstrecke zu erhalten.

The problem is solved by a method with the steps:

• a) measuring coordinates of an initial point of a route, hereinafter referred to as sub-section;
• b) measuring coordinates of an endpoint of the leg;
• c) calculating the Cartesian distance between starting point and end point;
• d) estimating the variance of the coordinates of at least one of the two points,
• e) decreasing the Cartesian distance by a positive value increasing with the variance to obtain the length of the leg.

The method is based on the insight that the result of a coordinate measurement is a random variable whose distribution is centered around the true coordinate value. If you think about the true coordinates z. For example, if the starting point is a sphere on whose surface the true endpoint is located, then less than half of the endpoint's distribution lies within the sphere, with the result that the distance calculated from coordinate measurements will be on average higher than the true distance , To correct this error, the greater the inaccuracy of the measurement, the more the calculated distance must be reduced.

Specifically, in step e), a correction term may be calculated as the root of a weighted difference of the squared Cartesian distance and the variance, and based thereon, the route length as the weighted sum of the Cartesian distance and the correction term.

It can be shown that for optimal correction in calculating the correction term, the weight of the variance in step e1) is four times as large as the weight of the squared Cartesian distance and should be weighted equally when calculating the path length of the correction term and the Cartesian distance.

The coordinate measurement is preferably carried out using satellite navigation signals.

The variance can then be estimated for each coordinate measurement individually based on the reception conditions of the satellite navigation signals, in particular based on the number and position of the satellites whose signals are received.

It can be provided a check whether the calculated in step c) Cartesian distance exceeds a predetermined minimum. If this is not the case, then - especially if the leg is part of a longer distance to be measured - the end point can be rejected as inappropriate, and on Based on an endpoint that has been redefined on the longer route, steps b) c) and e) can be repeated.

This minimum should be higher, the greater the variance of the coordinate measurement.

In particular, the minimum size should be high enough to ensure that the root mentioned above has a real value, i. H. the squared Cartesian distance should be so large that the weighted difference is at least zero.

An identical measuring device can be placed one after the other at the beginning and at the end of the section to perform the coordinate measurements of steps a) and b).

Preferably, this is a measuring device, which is carried on board a departing vehicle the vehicle.

In order to measure a nonlinear path, it should be split into sections and the method described above should be performed on each section. The thus obtained lengths of the sections can be added to obtain the length of the original route.

Partial sectioning should be done (i.e., the sections should be so long) that for each leg, the square is the weighted difference greater than or equal to zero.

If the entire route is not yet known (for example because the driver of the vehicle has not indicated his destination to a navigation device performing the method or because he deviates from a route planned by the navigation device), the end point of a partial route can not be determined until after the starting point of the Go through section and there the coordinate measurement of step a) has been performed.

In such a case, it is expedient to first define a time interval between steps a) and b) and to accept as the end point of the partial section the point at which the vehicle is located, if this time interval has elapsed since passing the starting point.

All motor vehicles have an odometer that measures the distance traveled based on the number of revolutions of the wheels. However, the measured value of such an odometer is subject to a systematic error if the diameter of the tires deviates from the value to which the odometer is calibrated. The

How big this interval should be can be decided dynamically based on the speed with which a previous leg has been covered. So z. B. ensure that the weighted difference is positive, unless the speed of the vehicle has decreased too much. If the speed has dropped sharply in a short time, z. B. when leaving a highway or when approaching a jam end, the end point can be discarded and redefined as described above. Optionally, the value of the weighted difference may be used to estimate when it is likely to become positive, to establish a time period based thereon, and to accept the point reached after the lapse of time as the newly established end point. All motor vehicles have an odometer that measures the distance traveled based on the number of revolutions of the wheels. However, the measured value of such an odometer is subject to a systematic error if the diameter of the tires deviates from the value to which the odometer is calibrated. The measuring method according to the invention is free from this systematic error. By comparing its result with a measured value of the conventional odometer, it can be detected whether the diameter of the tires deviates from the calibration value.

If the measured value of the conventional odometer is significantly higher than that of the method according to the invention, then the tire diameter is smaller than the calibration value, and a warning may be issued to the driver that the tire pressure may be too low or the tires have worn down.

If the comparison of present and past readings indicates that the tire diameter has increased, then this may justify a warning about possibly too high tire pressure.

Further subject matter of the invention is a computer program product having program code means enabling a computer system to carry out the method described above, a computer-readable medium recorded with program instructions enabling a computer to execute the method, and a computer which is programmed; to carry out the procedure.

A computer is to be considered in particular a vehicle navigation device, but also tablets or mobile phones, which are already conventionally equipped for receiving and evaluating the signals from navigation satellites, are considered.

• – Mitteln zum Messen (S2, S5) von Koordinaten (x₁) eines Anfangspunkts (5) der Teilstrecke und zum Messen (S5) von Koordinaten (x₂) eines Endpunkts (5) der Teilstrecke;
• – Mitteln zum Berechnen (S7) des kartesischen Abstands (d_err) zwischen Anfangspunkt (5) und Endpunkt (5) anhand der gemessenen Koordinaten (x₁, x₂);
• – Mitteln zum Abschätzen (S3, S6) der Varianz ( σ 2 / 1 , σ 2 / 2 ) der Koordinaten (x₁, x₂) wenigstens eines der beiden Punkte (5),
• – Mitteln zum Vermindern (S11) des kartesischen Abstands (d_err) um einen mit der Varianz ( σ 2 / 1 , σ 2 / 2 ) zunehmenden positiven Wert, um die Länge (d*) der Teilstrecke zu erhalten.

The subject of the invention is also a device measuring the length of a sub-section with:

• Means for measuring (S2, S5) coordinates (x ₁ ) of a starting point ( 5 ) of the sub-segment and for measuring (S5) coordinates (x ₂ ) of an end-point (S5) 5 ) of the leg;
• Means for calculating (S7) the Cartesian distance (d _err ) between starting point ( 5 ) and endpoint ( 5 ) based on the measured coordinates (x ₁ , x ₂ );
• Means for estimating (S3, S6) the variance ( σ 2/1 . σ 2/2 ) of the coordinates (x ₁ , x ₂ ) of at least one of the two points ( 5 )
• Means for reducing (S11) the Cartesian distance (d _err ) by one with the variance ( σ 2/1 . σ 2/2 ) increasing positive value to obtain the length (d *) of the leg.

Further features and advantages of the invention will become apparent from the following description of embodiments with reference to the accompanying figures. Show it:

1 a map display of traffic routes with a vehicle implementing the inventive method;

2 an enlarged section 1 ;

3 a block diagram of the vehicle;

4 a flowchart of the method.

1 shows that by a vehicle 1 from a start 2 to a destination 3 traveled track 4 , As can be seen immediately, a measurement of the coordinates of the start and finish 2 . 3 Although allow an exact calculation of their Cartesian distance D ₂₃ , since the inaccuracy of the coordinate measurements correspond to only a tiny fraction of D ₂₃ . Nevertheless, D _{23 would} only be an inadequate approximation to the length of the actual driveway 4 ,

A better approach to the actual path length is achievable when on the road 4 numerous measuring points 5 be set, the Cartesian distance between each two consecutively from the vehicle 1 visited measured points and the sum of the distances thus obtained is formed. On straight stretches such as a freeway 7 Distances between the measuring points of several 10 m can provide a satisfactory result, but not on inner-city streets 8th , Systematic errors are unavoidable when the actual path traveled between two measuring points has curves and clearly from the shortest connection between the measuring points, in 1 occasionally as straight segments 6 drawn, deviates.

To minimize the resulting systematic error, one would have to choose a distance between the measurement points that is smaller than the smallest curve radius that the vehicle 1 can drive. But then the problem arises that the inaccuracy of the coordinate measurement falsifies the result. 2 shows a section of the on the highway 7 driven track 4 , The driveway 4 is here for the sake of simplicity just ideal. Since the measurement of the coordinates is subject to a random error, the measured coordinates do not agree exactly with the true coordinates of the measuring points 5-1 . 5-2 , ... but denote points 9-1 . 9-2 , ..., which are randomly distributed around the true measuring points, with the result that one way 10 , which the vehicle appears to have covered along the driveway, zigzags and is significantly longer than the straight line of the actual driveway 4 ,

stehen. In der Praxis steht zwar nur ein einziger Messwert d_err für den Abstand zwischen den Messpunkten 5-1, 5-2 zur Verfügung, doch auch der kann analog zu der obigen Formel korrigiert werden, um einen berichtigten Abstandswert

zu erhalten, der wahrscheinlich näher am wahren Abstand d der Messpunkte 5-1, 5-2 liegt als der ursprüngliche Abstandsmesswert d_err.Assuming that the points 9-1 . 9-2 in each case around the associated measuring points 5-1 . 5-2 are normally distributed around, one can show that the true distance d between two measuring points 5-1 . 5-2 and the Average d of the errored distance d _err between the corresponding points 9-1 . 9-2 to each other in the relationship

stand. In practice, although only a single measured value d _{err stands} for the distance between the measuring points 5-1 . 5-2 but this too can be corrected by an adjusted distance value analogous to the above formula

which is probably closer to the true distance d of the measuring points 5-1 . 5-2 is the original distance measurement d _err .

3 shows a block diagram of the vehicle 1 , A radio interface 11 for receiving navigation signals is in a conventional manner with a computing unit 12 On the one hand, based on the satellite signals, a calculation of the position of the vehicle 1 and, on the other hand, estimates the variance of the position calculation or an equivalent value on the basis of parameters such as the position of the navigation satellites in the sky and the strength of the navigation signals received therefrom.

A control unit 13 is with a timer 14 connected to the position and variance of the arithmetic unit at timings given by the timer 12 inquire and in the following with reference to 4 process described. The units 12 . 13 can in one in the vehicle 1 built-in navigation device to be implemented; the control unit 13 can also from an on-board computer of the vehicle 1 are formed and query positions and variances of the computing unit of the navigation device. Since the method described below requires no further inputs except the positions and variances, it may also be on any one with a radio interface 11 equipped mobile computer running only temporarily in the vehicle 1 located, especially on a tablet or smartphone.

The method begins, manually initiated by the driver or, if the navigation device is connected to the on-board network of the vehicle, at the onset of the on-board voltage, with the initialization of a time interval between successive position measurements to an initial value .DELTA.t (step S1), a first measurement of the current Coordinates x _{1 of} the vehicle (step S2) and an estimate of the variance σ 2/1 this measurement (step S3). A suitable initial value Δt may be between 0.2 and 0.5 s.

After the waiting time Δt has elapsed in step S4, current coordinates x _{2 of} the vehicle are again measured (step S5) and their variance σ 2/2 estimated (step S6).

In the next step S7, the Cartesian distance d _err = | x ₂ -x ₁ |., _{Which is subject} to a random error due to the variances of x ₁ and x ₂ calculated between the coordinates. If the distance is similar to the standard deviations σ ₁ , σ _{2 of} the coordinates, then the vector difference x ₂ - x _{1 is} almost purely random and does not allow any conclusion about the actually traversed path. Therefore, the coordinates x _{2 are} discarded in step S8 if d _{err is} not at least equal to 2c | σ ₁ + σ ₂ | where c is a parameter that can be specified at will with a real value> 1. A value c = 4 is suitable.

If it has been decided in step S8 to discard the coordinates x ₂ , then the process may return to step S4, as indicated by a broken line, to repeat steps S5-S8 again when the waiting time Δt has elapsed.

If the vehicle 1 If it does not move very slowly, it may happen that coordinates are repeatedly calculated and then discarded. In order to avoid a blockage of computing power by superfluous calculations, it can be provided that in the event that a measured value must be discarded, the waiting time Δt is increased by an increment ε (S9). It can be an absolute upper limit of the waiting time .DELTA.t be predetermined, which is not exceeded in step S9, to To ensure that when the vehicle moves quickly again, this is soon detected. The value of the increment ε can be fixed or a function of d _err - 2c | σ ₁ + σ ₂ | be. After incrementing (S9), the process may return to step S4 to await the complete incremented wait time, or only the increment ε may be awaited (S10) before a new coordinate measurement is taken.

berechnet, und die gespeicherten Koordinaten x₁ sowie die zugehörige Varianz σ 2 / 1 werden mit x₂ bzw. σ 2 / 2 überschrieben (S12).If it has been determined in step S8 that the coordinates x _{2 are} usable, the corrected distance d * is calculated according to the formula in step S11

calculated, and the stored coordinates x ₁ and the associated variance σ 2/1 become with x ₂ resp. σ 2/2 overwritten (S12).

und diese empirisch zu optimieren. Denkbar ist auch, zur Verminderung des Rechenaufwands den Wurzelterm in eine Taylorreihe nach ( σ 2 / 1 + σ 2 / 2 ) oder d_err zu entwickeln, die nach einer kleinen Zahl von Summanden abbricht.It is understood that not every practical implementation of the method needs to work with this formula. Although it is assumed that in the case of normally distributed coordinates x ₁ and x _2, this formula allows an optimal approximation to the true distance; In order to take account of possible deviations of the coordinate measured values from a normal distribution, it may be useful to generalize the formula by weighting coefficients a, b:

and to optimize these empirically. It is also conceivable to reduce the computational effort of the root term in a Taylor series after ( σ 2/1 + σ 2/2 ) or d _err , which breaks off after a small number of summands.

It may be provided a step S13, in which it is checked whether d _{err is} possibly greater than desired for optimal measurement accuracy. If d _err exceeds a threshold thr, preferably a multiple of 2c | σ ₁ + σ ₂ |, Δt is reduced in step S14.

The corrected distance d * is added to a count value D of an odometer in step S15; then the process returns to step S4.

The driveway 4 is decomposed in this way into a large number of partial sections whose lengths d * are individually calculated and added up. Although each individual section d * is subject to a random error due to the inaccuracy of the coordinate measurement, but these errors cancel each other on average, so that nevertheless an accurate distance measurement is possible.

It should be understood that the foregoing detailed description and drawings, while indicating certain exemplary embodiments of the invention, are intended for purposes of illustration only and are not to be construed as limiting the scope of the invention. Various modifications of the described embodiments are possible without departing from the scope of the following claims and their equivalence range. In particular, this description and the figures also show features of the embodiments which are not mentioned in the claims. Such features may also occur in combinations other than those specifically disclosed herein. Therefore, the fact that several such features are mentioned in the same sentence or in a different type of textual context does not justify the conclusion that they can occur only in the specific combination disclosed; instead, it is generally to be assumed that it is also possible to omit or modify individual ones of several such features, provided this does not call into question the functionality of the invention.

LIST OF REFERENCE NUMBERS

1

vehicle

2

begin

3

aim

4

roadway

5

measuring point

6

straight segment

7

expressway

8th

inner city street

9

Point

10

(apparent) way

11

Radio interface

12

computer unit

13

control unit

14

timer

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102014211164 A1 [0005]

Claims (15)

Method for measuring the length of a partial section, comprising the steps of: a) measuring (S2, S5) coordinates (x ₁ ) of a starting point ( 5 ) of the leg; b) measuring (S5) coordinates (x ₂ ) of an endpoint ( 5 ) of the leg; c) calculating (S7) the Cartesian distance (d _err ) between starting point ( 5 ) and endpoint ( 5 ) based on the measured coordinates (x ₁ , x ₂ ); d) estimating (S3, S6) the variance ( σ 2/1 + σ 2/2 ) of the coordinates (x ₁ , x ₂ ) of at least one of the two points ( 5 ), e) decreasing (S11) the Cartesian distance (d _err ) by one with the variance ( σ 2/1 + σ 2/2 ) increasing positive value to obtain the length (d *) of the leg. The method of claim 1, wherein step e) comprises the steps of: e1) calculating a correction term as the root of a weighted difference of the squared Cartesian distance (d _err ) and the variance ( σ 2/1 + σ 2/2 ) and e2) calculating the distance (d *) as the weighted sum of the Cartesian distance (d _err ) and the correction term. Method according to Claim 2, in which the weight of the variance ( σ 2/1 + σ 2/2 ) in step e1) is four times as large as the weight of the squared Cartesian distance (d _err ). The method of claim 2 or 3, _wherein the correction term and the Cartesian distance (d _err ) are weighted equally in step e2). Method according to one of the preceding claims, with the additional steps f) checking (S8) whether the calculated Cartesian distance (d _err ) exceeds a predetermined minimum size, and if not, g) re-establishing (S9, S10) the end point (S8) 5 ) and repeating steps b), c) and e). The method of claim 5, wherein the minimum is an increasing function of the variance ( σ 2/1 + σ 2/2 ). Method according to one of the preceding claims, in which a measuring device for carrying out step a) at the starting point ( 5 ) and for carrying out step b) at the end point ( 5 ) of the leg is placed. Method according to Claim 7, in which the measuring device is mounted in a vehicle ( 1 ) and the leg of the vehicle ( 1 ) is traversed. Method for measuring the length of a route with the steps - disassembling the route ( 4 ) in sections; Measuring the lengths (d *) of the sections by a method according to one of the preceding claims, and adding (S15) the lengths (d *) of the sections to the length (D) of the section ( 4 ) to obtain. Method according to claim 9, as far as dependent on claim 2, in which the division into sub-sections is performed such that for each sub-section the weighted difference is greater than or equal to zero (S8). Method according to Claim 10, in which the end point ( 5 ) of a partial route after the implementation of the step a) for the partial route is determined (S4). The method of claim 11, wherein the endpoint ( 5 ) of a partial route is set by waiting a time interval (Δt) between step a) and step b) for this partial route (S4). Method according to Claim 12, in which the time interval (Δt) is determined as a function of the speed (S9, S14) with which a preceding partial route has been traveled. Computer program product with program code means which enable a computer, in particular a car navigation device, a tablet or a mobile telephone, to carry out the method according to one of claims 1 to 13. Computer programmed to carry out the method according to one of claims 1 to 13.

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