JPH0567192B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is directed to GPS (Global Positional System).
system) related to navigation.

[Conventional technology]

GPS navigation is a navigation method in which the user determines the distance between himself and each satellite by using radio waves from multiple satellites tracing polar orbits, and then calculates the position continuously.

Now, the coordinate system is an earth-centered, earth-fixed Cartesian coordinate system, and the user coordinates are X, Y, Z,
Let the satellite coordinates be SX _i , SY _i , SZ _i (1<i<n).
The distance to each satellite measured using radio waves is called the pseudo range PD _i , and is related to the coordinates and the following formula.

PD _i = √( _i −) ² + ( _i −) ² + ( _i ) ² −C・
B
...(1) Here, C is the speed of light and B is the time offset.

Note that this measured value is used separately as MSR.
Generally speaking, in GPS navigation, there are 4
MSR ₁ = f (SX ₁ , SY ₁ , SZ ₁ , X, Y, Z, B) MSR ₂ = f (SX 2 , SY ₂ , SZ ₂ , X _, Y, Z, B) ) MSR ₃ = f (SX ₃ , SY ₃ , SZ ₃ , X, Y, Z, B) MSR ₄ = f (SX ₄ , SY ₄ , SZ ₄ , X, Y, Z, B) ...(2) Solving the above simultaneous position equations expressed as
This is to find Y, Z, and B. In the simultaneous position equations, the satellite coordinates SX ₁ , SY ₁ , SZ _{1 .} . . are known, and MSR _{1 .} . . are values determined from measured values.

[Problem that the invention seeks to solve]

As variables for the simultaneous position equations, the coordinate system is a special curved coordinate system that is earth-centered and earth-fixed (latitude LT,
Longitude LG, height HT, time offset B) can also be used. This is also a common practice in navigation. Note that in the following, when a coordinate system is referred to, it includes a time offset as described above. Since simultaneous position equations are nonlinear multivariable equations, they are usually linearized by considering partial differential values of functions with respect to variables. Simultaneous position equations for the curved coordinate system have many problems in numerical calculations, such as unbalanced coefficients on variables and the occurrence of singular points, which increases the number of convergence times and increases calculation processing time and errors. It tends to get bigger. On the other hand, in the Cartesian coordinate system format, the simultaneous position equations are simple calculation formulas as shown in equation (1), so the above problem is less likely. Therefore, it is advantageous to obtain a solution in the Cartesian coordinate system and then finally transform it into a curved coordinate system.

However, since the Cartesian coordinate system is determined without regard to the shape of the earth, it is difficult to consider each of its components independently, resulting in the following problem. When GPS navigation is used on ground vehicles, satellites often get behind obstacles such as mountains or built structures, resulting in less than four satellites being able to be detected. If there are no obstacles, it is possible to capture 4 satellites in most cases if the number of satellites launched reaches the planned number, but with the current number of satellites being small, the time it takes to capture 4 or more satellites is limited. Very short. However, even if the number of satellites that can be captured is 3 or less, the number of variables equivalent to the difference number DN (= 4 - VN, VN is the number of captured satellites) from the case of 4 is set as a fixed value (unchanged estimated value). In a situation where this is possible, it should be possible to create simultaneous position equations with the number of equations corresponding to the number of VNs, and obtain the user position as the solution. The earth-centered and earth-fixed curved coordinate systems LT, LG, HT,
In case B, for example, if you are moving in a place where the height does not change much, the estimated height at that time (if four or more satellites were previously detected and the height was determined) For example, by fixing it to the current value) and reducing the variables to three, LT, LG, and B, three simultaneous position equations can be assembled. Furthermore, if B can be fixed to an estimated value, the number of simultaneous equations can be reduced to two. However, in the case of Cartesian coordinate system Cannot be set. As a Cartesian coordinate, only the time offset can be estimated from rational grounds and taken to be a constant value.

From the above, it can be seen that if the simultaneous position equations are written in a Cartesian coordinate system, it is advantageous in terms of arithmetic processing, but it is not advantageous if the number of captured satellites is less than four.

The object of the present invention is to eliminate the above-mentioned drawbacks, display simultaneous position equations in a Cartesian coordinate system, and provide a GPS navigation calculation processing method that can perform calculations rationally even when the number of acquired satellites is less than four. The present invention also provides a GPS navigation arithmetic processing device using the method.

[Means for solving problems]

The GPS navigation calculation processing method of the present invention includes the following processing.

(a) Latitude, longitude, height, and time offset
If the number of captured satellites is less than 4, DN of the 4 variables, i.e. (4 - number of captured satellites), is kept unchanged. The user's estimated position is input as the user's estimated position, and the inputted user's estimated position is divided into four variables consisting of three position variables and a time offset.
The process of converting to the user's estimated position in a Cartesian coordinate system with DN variables, of which DN are kept unchanged.

(b) virtualized at an appropriate position in the Cartesian coordinate system
The pseudorange PD of each of the DN virtual satellites is calculated from the user's estimated position in the transformed Cartesian coordinate system, and the virtual result is used as the virtual satellite.
Virtual satellite MSR determination process to determine as MSR.

(c) four satellites that may include said virtual satellite MSR;
A process of creating four simultaneous position equations in the Cartesian coordinate system from the MSR.

(d) A process of solving the previously created simultaneous position equations to obtain four solutions.

(e) Reset the number of solutions obtained by removing the one that will remain unchanged from the four solutions obtained in (d) above as the new value of the user's estimated position in the Cartesian coordinates transformed in (a) above. After that, iterative processing that repeats the processing from (b) to (d) above.

(f) Determine the convergence of the iterative processing, and if convergence occurs, end the iterative processing, convert the solution of the simultaneous position equations to a curved coordinate system and output it as a calculation result, and if it does not converge, terminate the iterative processing. Judgment process to cancel.

[Effect]

When the number of captured satellites is less than 4, the DN variables are selected in a curved coordinate system and are assumed to be constant estimates. Below, all variables are converted to Cartesian coordinates. The four simultaneous position equations are MSR, and the DN equations are those in which the condensed range is calculated assuming that the virtual satellite is located at one of the positions in the Cartesian coordinate system. The four simultaneous position equations are expressed in a Cartesian coordinate system, and the variables for their solutions can be obtained relatively easily. The pseudo range of the virtual satellite is recalculated using the obtained variables as new estimated values, and the iterative calculation process is performed to form the simultaneous position equations again as the MSR. Once the final calculation result is obtained by determining the convergence conditions for the iterative calculation process, it is displayed and output in a curved coordinate system.

〔Example〕

Hereinafter, one embodiment of the present invention will be described with reference to the drawings. In this example, there are three captured satellites, and the user's height is an invariant estimate (fixed) KHT. The calculation processing method will be explained with reference to the flowchart of FIG. Difference in captured satellites
Since DN=1, only one virtual satellite is required. In this example, it is placed at the center of the earth. The virtual satellite can be any point in the air, on the ground, or inside the earth, but if the line of sight from the user's estimated position to the virtual satellite is in the same direction as the acquired satellite, the variables will no longer be independent, so this must be avoided. It won't happen. This cannot happen in a geocentric setting.

First, at (PO), the Cartesian coordinates of captured satellites S ₁ , S ₂ , S ₃ and the measured value of the pseudo range of each satellite
MSR _i : Enter 1 to 3. Here, the former is calculated by another routine using the orbital parameters of each satellite and the user's clock. The latter is the value obtained from the receiver.

In (P1), the user inputs the estimated latitude PLT, estimated longitude PLG, height KHT (fixed), and estimated time offset PB. The initial P indicates an estimated value. The estimated value can be quite arbitrary, but
The closer the value is to the true value, the fewer the number of iterative calculations will be required. When satellite data is continuously input and calculated, the previous calculation results are automatically input. The height is a fixed value in this example.

Next, in (P2), the user coordinates are converted to coordinates in the Cartesian coordinate system. Note that although the time offset is unrelated to the coordinate system, when referring to each coordinate system, it is included in each coordinate system.

Next, at (P3), the virtual satellite S ₄ placed at the center of the earth
Calculate the pseudo range of from the user estimated coordinates,
This is called MSR ₄ . Therefore, as shown in (P4), the MSR is determined for the four satellites S ₁ to S ₄ ,
The simultaneous position equations shown in equation (2) are created. Next, in (P5), when the simultaneous position equations are set, the user position
Calculate Y, Z and time offset B. Next, in (P6), the corresponding curved coordinate positions LT, LG, and HT are calculated from the user positions X and YZ.

The determination processing means for determining the end of repetition, etc. cannot be uniquely determined, and various methods can be considered. In the case of this figure 1, one of the captured satellites is (P7),
Each pseudo range for one of the virtual satellites
PD1 and PD4 are calculated, and in (P8) it is examined whether the absolute value difference with MSR ₁ and MSR ₄ is within the minute difference EPS. If it is within EPS, output as the measured LT, LG, KHT, and B at (P10). Note that the HT calculated in (P6) is the fixed value entered in (P1).
Even if there may be some differences from KHT,
Output as KHT.

If the difference is not within the small difference EPS, in (P9), KHT is left as is, and the other variables LT, LG, and B are set to the estimated value PLT, because of the iterative calculation.
Replace as PLG and PB, return to (P2), and perform the iterative operation.

By the way, in the process of the flowchart in Figure 1,
If the height setting value KHT (fixed) is far from the true value, the accuracy of time offset B, latitude LT, and longitude LG will be degraded by that amount. The set value KHT must be as close to the true value as possible, but if you are driving on flat ground, you can easily find out the altitude of your current location from the contour lines on the map.

As mentioned above, various convergence determination conditions can be considered. For example, in Figure 1 (P8), MSR and
The difference from PD is calculated, but since the user coordinates (latitude, longitude, height, time offset) in the curved coordinate system are first entered as estimated values, each calculated value is calculated as the difference from the estimated value. The absolute value of
If the value is less than or equal to EPS, it is assumed that the calculation was performed correctly, and the calculation can be terminated. The conditional expressions for determining the absolute value of the difference between each coordinate value and its estimated value are as follows: ABS(LT-PLT)<EPS1, ABS(LG-PLG)<EPS2, ABS(HT-KHT)<EPS3 , ABS(B-PB)<EPS4 are all satisfied.

Next, an apparatus using the arithmetic processing method of the present invention will be explained with reference to FIG. This device consists of a satellite navigation receiving section 1, an arithmetic processing section 2, and a display section 3. The arithmetic processing section 2 includes a CPU 23, a program ROM, and a memory 24 including a temporary memory RAM.
and the calculated latitude LT, longitude LG, and height.
It has a data memory RAM 25 that stores numerical values such as HT and time offset. However, the RAM memory does not have to be physically divided into individual units of memory. The arithmetic processing section 2 has an input port 21 that receives input from a console 20 for setting initial values and the like, the satellite navigation receiving section 1, and an output port 22 that outputs the results of arithmetic processing.

The arithmetic processing unit 2 obtains data from the satellite navigation receiving unit 1 and performs processing using the arithmetic processing method described in the present invention.
The calculation is performed until the next reception, and the user coordinate data is obtained and stored in the data memory 25. By using the data stored in the data memory 25 as an estimated value when receiving the next received data, the user position can be continuously estimated. The operation console 20 is
This is used in the initial setting or when the height HT is set to the fixed value KHT in the previous embodiment, but this value is inappropriate and needs to be corrected. If the calculation in FIG. 1 is impossible and the process ends, the fixed value is manually corrected and the calculation process is performed using the next GPS received data.
The display unit 3 appropriately displays the results of the calculation process numerically or graphically. In addition to obtaining the pseudorange PD with the satellite as a measured value, the satellite navigation receiving unit 1 also uses necessary data as satellite information, such as orbit parameter data from each satellite and a user clock, to obtain the Cartesian coordinate system of the satellite. Value S _i
It is also possible to calculate X, S _i Y, and S _i Z and output them to the arithmetic processing section 2.

〔Effect of the invention〕

As explained above, if the arithmetic processing method of the present invention is used, position calculations for GPS navigation can be performed with reasonable estimates even when the number of captured satellites is less than four.
Simultaneous position equations can be solved by incorporating this into some of the GPS navigation variables. Since these simultaneous position equations are assembled using a Cartesian coordinate system, calculations are simple and the accuracy and speed of calculations can be improved. Even if the number of captured satellites is 4, in the flowchart of Figure 1, the captured satellites i = 1 to 1, except for the process related to virtual satellites.
It can be done in exactly the same way by simply changing 3 to i=1 to 4. Therefore, the calculation process can be performed in a unified manner regardless of whether the number of captured satellites is four or less than four.

Furthermore, the GPS navigation processing device using the method of the present invention is extremely advantageous in terms of navigation because it can continuously calculate satellite information in a unified manner under any environmental conditions.

[Brief explanation of drawings]

FIG. 1 is a flowchart showing an embodiment of the method of the present invention, and FIG. 2 is a block diagram of an example of the arithmetic processing device of the present invention. 1... Satellite navigation receiving section, 2... Arithmetic processing section, 3
...Display unit, 20...Operation console, 21...Input port, 22...Output port, 23...CPU, 2
4...Memory, 25...Data memory.

Claims (1)

[Claims] 1. In GPS navigation in which a user captures a satellite, obtains the satellite's position information and the measured value MSR of the pseudo range PD between the satellite and calculates the user's position from simultaneous position equations. , (a) latitude, longitude, height, and time offset.
(However, if the number of captured satellites is less than 4, DN (= 4 - number of captured satellites) of the 4 is kept unchanged). Enter it as the user's estimated location,
The input estimated user position is expressed in four variables consisting of three position variables and a time offset (however,
If the number of captured satellites is less than 4, the DN of the 4
(b) converting each of the pseudo ranges PD of the DN virtual satellites virtualized to appropriate positions in the Cartesian coordinate system into a user estimated position in a Cartesian coordinate system with a virtual satellite MSR determination process of calculating from the user's estimated position in the transformed Cartesian coordinate system and each virtual position of each virtual satellite, and determining the calculation results as DN virtual satellite MSRs; (c) the above (b) ) to create four simultaneous position equations in the Cartesian coordinate system from four MSRs that may include the DN virtual satellite MSRs determined in (d) the process of creating four simultaneous position equations in the Cartesian coordinate system; The process of solving and finding four solutions, and (e) keeping unchanged from the four solutions found in (d) above.
After resetting the number of solutions excluding DN as new values of the user's estimated position in the Cartesian coordinate system, repeat the processes from (b) to (d) above, or The number of solutions obtained by excluding the DN number, which is kept unchanged, from the four solutions obtained is converted to the position in the curved coordinate system, and set as the new value of the user's estimated position in the curved coordinate system. after,
an iterative process of repeating the processes from (a) to (d); and (f) determining convergence of the iterative process, and if convergence is found, finishing the iterative process and converting the solution of the simultaneous position equations into a curved coordinate system. A GPS navigation calculation processing method, comprising: a determination process of converting the resultant into a calculation result and outputting the result as a calculation result, and stopping the iterative process if the convergence does not occur. 2. The determination process in (f) above determines whether the pseudo range calculated from the solution of the simultaneous position equations for one of the virtual satellites and one or both of the captured satellites is the captured satellite.
From the MSR, in the case of a virtual satellite, the said virtual satellite
2. The GPS navigation calculation processing method according to claim 1, wherein convergence is determined if it is within a predetermined minute range from the MSR. (a ) Latitude, longitude, height and time offset 4
(However, if the number of captured satellites is less than 4, DN (= 4 - number of captured satellites) of the 4 is kept unchanged). Enter it as the user's estimated location,
The input estimated user position is expressed in four variables consisting of three position variables and a time offset (however,
If the number of captured satellites is less than 4, the DN of the 4
(b) each of the DN virtual satellites virtualized at an appropriate position in the Cartesian coordinate system; (c) virtual satellite MSR determining means for calculating a range PD from the user's estimated position in the transformed Cartesian coordinate system and each virtual position of each virtual satellite, and determining the calculation results as DN virtual satellite MSRs; means for creating four simultaneous position equations in the Cartesian coordinate system from four MSRs that may include the DN virtual satellite MSRs determined in (b) above; (d) the created simultaneous position equations; (e) means to solve the position equation to obtain four solutions, and (e) remain unchanged from the four solutions obtained in (d) above.
After resetting the number of solutions excluding DN as new values of the user's estimated position in the Cartesian coordinate system, repeat the processes from (b) to (d) above, or The number of solutions obtained by excluding the DN number, which is kept unchanged, from the four solutions obtained is converted to the position in the curved coordinate system, and set as the new value of the user's estimated position in the curved coordinate system. after,
an iterative means for repeating the processes from (a) to (d); (f) determining convergence of the iterative process by the iterating means, and if convergence is found, finishing the iterative process and solving the simultaneous position equations; (g) a determining means for converting into a curved coordinate system and outputting the result as a calculation result, and stopping the iterative processing if the result does not converge; (g) storing the calculation result output by the determining means;
A GPS navigation arithmetic processing device comprising: a calculation result storage/supply means for supplying the user's estimated position to the input/conversion means in the next calculation.