JP6291916B2 - Correction data distribution server - Google Patents

Description

  The present invention relates to a correction data distribution server that generates and distributes correction data for improving positioning accuracy using observation data received from an electronic reference point. In particular, the present invention relates to a correction data distribution server capable of continuing the distribution of correction data even when an electronic reference point is moved due to a crustal movement such as an earthquake.

The conventional GNSS (Global Navigation Satellite System) correction data distribution server uses the coordinates of the electronic reference point distributed separately from the observation data received from the electronic reference point distributed from the Geospatial Information Authority of Japan. Analyze and generate correction data depending on time and place.
The user can calculate the coordinates of the user's GNSS receiver with high accuracy by using correction data received by the network or the GNSS receiver as observation data received by the GNSS receiver possessed by the user. (For example, refer to Patent Document 1).

JP 2006-105721 A

However, since the conventional GPS correction data distribution server uses the electronic reference point coordinates as known points, correct correction data cannot be generated if the electronic reference point coordinates differ from the actual point. The reason why the electronic reference point coordinates are different from the actual one is, for example, the occurrence of an earthquake, and when the electronic reference point itself moves due to the earthquake, it may be different from the value of the distributed electronic reference point coordinates.
As mentioned above, when the electronic reference point located in the immediate vicinity of the user cannot be used, correction data created at a long-distance electronic reference point must be used, but generally when the distance from the electronic reference point becomes long There existed a subject that the positioning accuracy of a user's GNSS receiver fell.

  The present invention has been made to solve such a problem, and even when the electronic reference point moves due to an earthquake or the like, and the stored electronic reference point coordinates are different from the actual coordinates, it is automatically performed. An object of the present invention is to provide a correction data distribution server that detects movement of an electronic reference point and continues distribution of correction data based on the electronic reference point coordinates after the movement.

The correction data distribution server according to the present invention is a correction data distribution server that generates and distributes correction data for positioning using reception information received by a plurality of electronic reference points from a GNSS satellite, wherein the electronic reference point The electronic reference point without movement is extracted from the electronic reference points installed around the moved electronic reference point, and the extracted position of the electronic reference point without movement is extracted. Temporary correction data is generated using reception information received by the electronic reference point having no movement, the post-movement position of the moved electronic reference point is calculated using the temporary correction data, and the moved Correction data is newly generated and distributed using the position after movement of the electronic reference point and the received information received by the electronic reference point after movement.

  According to the electronic reference point data distribution server according to the present invention, even when the electronic reference point moves due to an earthquake or the like, the electronic reference point coordinates after the movement are detected by the automatic recovery operation by detecting the movement of the electronic reference point. Since the distribution of the correction data is continued based on this, the user can continuously obtain the positioning result with high accuracy.

It is a figure explaining the arrangement | positioning and data flow of the electronic reference point which concerns on Embodiment 1 of this invention, a GPS satellite, a correction data delivery server, and the GPS receiver which a user possesses. It is the schematic showing the structure of the correction data delivery server which concerns on Embodiment 1 of this invention. It is a flowchart explaining operation | movement of the correction data delivery server which concerns on Embodiment 1 of this invention. It is the figure which showed the flow of the movement determination of the electronic reference point which concerns on Embodiment 1 of this invention. It is the figure which showed the creation flow of the temporary correction range which concerns on Embodiment 1 of this invention. It is a figure explaining the temporary correction range which concerns on Embodiment 1 of this invention. It is the figure which showed the detailed flow of the coordinate recalculation of the electronic reference point which concerns on Embodiment 1 of this invention.

Embodiment 1.
FIG. 1 shows a correction data distribution server 100 (hereinafter referred to as “distribution server 100”), an electronic reference point P (P1, P2,..., Pn), a GPS satellite S (S1,. S) is a diagram for explaining the arrangement and data flow of the GPS receiver T possessed by the user. The distribution server 100 is installed in a central center 110 that is connected to electronic reference points P installed throughout the country and exchanges information with the electronic reference points nationwide. The GPS satellite is an example of a GNSS satellite and may be a positioning satellite other than the GPS satellite. Electronic reference points P and GPS satellites are assigned numbers (1, 2, 3,..., N) for distinguishing them.

The distribution server 100 receives observation data 210 (210-1, 210-2,..., Received from a plurality of electronic reference points P (P1, P2,..., Pn) installed at predetermined intervals throughout the country. 210-n) is analyzed using the coordinates of each electronic reference point distributed separately to generate correction data 300 depending on time and place, and the generated correction data 300 is transmitted to the user via the network. Or, it is delivered on radio waves from GNSS satellites or ground stations.
The user corrects the observation data 210 from the GPS satellite S received by the GPS receiver T possessed by the user using the correction data 300, thereby calculating the position (also referred to as coordinates) of the current location with high accuracy. Can do.

  There are various types of correction data 300 depending on time and place. As an example, there is an error plane parameter representing an error plane. The error plane parameter is disclosed in Japanese Patent Application Laid-Open No. 2001-228234 and the like. If this error plane parameter is described with reference to FIG. 1, the distribution server 100 includes navigation messages from the respective electronic reference points P1 to Pn. Based on the GPS satellite information, the positions of the respective reference stations R1 to Rq are calculated, and a difference between the calculation result and the absolute positions of the electronic reference points P1 to Pn that are known in advance is used as error data to obtain a plurality of electronic An error plane is obtained from the error data at the reference points P1 to Pn. The parameter representing the error plane is an error plane parameter, and the distribution server 100 distributes the error plane parameter as correction data 300.

  The GPS receiver T owned by the user has a receiving function for receiving GPS satellite information necessary for positioning including navigation messages from a plurality of GPS satellites S, a receiving function for receiving error plane parameters from the distribution server 100, and its own position. It is possible to measure the current coordinate position with high accuracy on the order of centimeters, with the function of obtaining the error of the error from the error plane parameter from the single positioning result, and correcting with the error plane parameter of the position obtained by the single positioning. .

Here, since the distribution server 100 uses the coordinates where the respective electronic reference points P1 to Pn are set as known points, the correct correction is made when the coordinates of the current electronic reference point are different from the known coordinates. Data 300 cannot be generated.
The user (GPS receiver T) who acquires the correction data 300 and corrects the observation data cannot acquire an accurate position.
The cause of the difference in the coordinates of the electronic reference point from the current position of the electronic reference point P is, for example, the occurrence of an earthquake. When the electronic reference point P itself moves due to the occurrence of an earthquake, the actual position of the electronic reference point is different from the position coordinates of the known electronic reference point.
In the example of FIG. 1, the distance between the GPS satellite S and the electronic reference point Pn at time t is ρ, but at the next moment (t + Δt), the electronic reference point Pn moves by a distance ΔL due to an earthquake or the like. As a result, the actual distance between the GPS satellite S and the electronic reference point Pn is (ρ ′ + Δρ), and an error of Δρ occurs compared to the distance ρ calculated from the known electronic reference point. Since the distribution server 100 calculates correction data with the distance between the GPS satellite S and the electronic reference point Pn at time (t + Δt) as ρ ′, the calculated correction data includes an error or the calculation calculation does not converge. .

  On the other hand, when the electronic reference point P at a short distance from the user stops functioning due to an earthquake or the like, the user is generated based on observation data at the electronic reference point P located at a farther distance from the user. The observation data must be corrected using the correction data 300 and the coordinates of the current position must be calculated. As the distance from the user to the electronic reference point used to generate the correction data 300 increases, the GPS receiver T There is a problem that the positioning accuracy decreases.

FIG. 2 is a diagram showing a configuration of distribution server 100 according to the present embodiment.
The distribution server 100 includes an electronic reference point observation data receiving unit 10, an electronic reference point evaluation unit 20, an electronic reference point selection unit 30, a correction data generation unit 40, a recording unit 50, and an electronic reference point position calculation unit 60.
The distribution server 100 receives each observation data 210 (210-1, 210-2,..., 210-n) from a plurality of electronic reference points P (P1, P2,..., Pn) and generates correction data. To do. If it is determined that the electronic reference point P has moved, the coordinates of the moved electronic reference point P ′ are output. The electronic reference point 200 receives observation data from a plurality of GPS satellites S (S1,..., Sn).
Hereinafter, the function of each component of the distribution server 100 will be described.

(1) Electronic reference point observation data receiving unit 10:
Observation data 200 periodically transmitted from the electronic reference point P is received. The observation data 200 is GPS satellite information necessary for positioning including a navigation message. The electronic reference point observation data receiving unit 10 outputs the received observation data 200 to the electronic reference point evaluation unit 20 and the correction data generation unit 40. Data such as observation data 200 is recorded by a recording unit.

(2) Electronic reference point evaluation unit 20:
The electronic reference point evaluation unit 20 receives warning information received from an external organization in the event of an earthquake, etc., electronic reference point observation data received from the electronic reference point observation data reception unit 10, and statistics of past electronic reference point observation data Satellite-electronic reference point relative position information, which is a relative positional relationship between a GPS satellite and an electronic reference point, and an electron which is a relative positional relationship between a plurality of electronic reference points based on the electronic reference point coordinate value obtained from the value The relative position information between reference points is calculated.
Then, based on the calculated satellite-electronic reference point relative position information and the electronic reference point relative position information, it is determined whether or not the electronic reference point P has moved. When it is determined that the movement is determined by the determination, the corresponding electronic reference point number is notified to the electronic reference point selection unit. A method for determining whether or not the electronic reference point has moved will be described later.

(3) Electronic reference point selection unit 30:
With respect to all the electronic reference points P determined to have moved by the electronic reference point evaluation unit 20, another electronic reference point that is close to the electronic reference point P determined to have moved is selected, and whether or not there has been movement Confirm. If it is determined to move, it is next checked whether or not the coordinates of the electronic reference point have been updated.
Electronic reference point selection when other electronic reference points that are close in distance based on the electronic reference point P determined to be moved are determined not to move, or when coordinate update is completed after the movement is determined The unit 30 passes the corresponding electronic reference point number to the correction data generation unit 40, and generates correction data around the electronic reference point determined to be moved.
When it is determined that the electronic reference point having a close distance is moved, the electronic reference point position calculation unit 60 does not perform the next process until the coordinates of the electronic reference point having the close distance are updated.
The electronic reference point with a short distance is an electronic reference point within, for example, 20 km to 60 km, and this distance can be changed.

(4) Correction data generation unit 40:
The electronic reference point number of the electronic reference point determined to be moved is received from the electronic reference point selection unit 30. Next, correction data at the location of the electronic reference point determined to be moved is generated using the observation data received by the electronic reference point that has been determined to be moved and is not determined to be moved. . Here, the correction data indicates ionospheric delay, tropospheric delay, satellite clock error, satellite orbit error, and signal bias.

(5) Recording unit 50:
The recording unit 50 includes observation data that each electronic reference point has observed from a GPS satellite in the past, electronic reference point coordinates that are coordinates at which each electronic reference point is installed, satellite-electronic reference point relative position information, electronic reference Various data such as determination results obtained by determining whether or not the electronic reference point is moved is stored for the relative position information between the points and each electronic reference point.

(6) Electronic reference point position calculation unit 60:
The electronic reference point position calculation unit 60 uses the correction data generated by the correction data generation unit 40 around the electronic reference point determined to be moved and the observation data of the moved electronic reference point determined to be moved. Is calculated, that is, the coordinates of the electronic reference point after movement are calculated.
The electronic reference point position calculation unit 60 updates the coordinates of the electronic reference point recorded in the recording unit 50 to the calculated coordinates of the electronic reference point after movement.
The electronic reference point position calculation unit 60 passes the electronic reference point number with updated coordinates to the electronic reference point selection unit so that it can be used to generate correction data.

Next, the distribution server 100 determines whether or not the position of the electronic reference point P has changed due to the occurrence of an earthquake. If there is a change in position, the distribution server 100 newly generates correction data 300 and sends the correction data 300 to the user. The distribution operation will be described.
FIG. 3 is a flowchart for explaining the operation of the distribution server 100. The outline will be described below with reference to the drawings.

  The distribution server 100 receives warning information 400 indicating that an earthquake has occurred from a public institution (not shown) that has detected the earthquake at the timing of the occurrence of the earthquake (step S01).

The electronic reference point evaluation unit 20 periodically receives observation data 210 (210-1 to 210-n) received at each electronic reference point P (P1 to Pn) from the electronic reference point observation data receiving unit 10.
When the electronic reference point evaluation unit 20 receives the alarm information 400, the electronic reference point evaluation unit 20 determines whether each electronic reference point P (P1 to Pn) has moved due to the earthquake (referred to as “movement determination”) (S02).
Here, the electronic reference point evaluation unit 20 performs the movement determination by 1) relative positional relationship between the GNSS satellite and the electronic reference point P (satellite-electronic reference point relative position information), and 2) relative positions of a plurality of electronic reference points. A determination is made based on the relationship (relative position information between electronic reference points).
1) Regarding the relative positional relationship between the GNSS satellite and the electronic reference point P, the distance between the GNSS satellite and the electronic reference point P is measured, and when the difference in distance before and after the occurrence of the earthquake is greater than or equal to a predetermined threshold, the electronic reference It is determined that the point P has moved. The distance between the GNSS satellite and the electronic reference point P can be measured with high accuracy (mm accuracy) by detecting the phase difference of the carrier wave transmitted by the GNSS satellite.
On the other hand, 2) With respect to the relative positional relationship between a plurality of electronic reference points P, four or more GNSS satellites are observed at a plurality of electronic reference points P for a long period of time, and a high accuracy ( relative accuracy is calculated. Then, it is determined that the electronic reference point that has changed more than the set value in this relative positional relationship has been moved.
Here, in the relative positional relationship of 1), when the difference in distance generated before and after the occurrence of the earthquake is an integral multiple of the phase of the carrier wave (for example, 19 cm), the electronic reference point P can be erroneously recognized as not moving. There is sex. In addition, in the relative positional relationship of 2), when the crust where the plurality of electronic reference points P are installed is the same crust, there is no change in the relative positional relationship, and it may be erroneously recognized that the electronic reference point P does not move. There is sex.
Therefore, in the present embodiment, satisfying both 1) and 2) is used as a determination criterion for movement determination.

  The relative positional relationship between the GNSS satellite and the electronic reference point P is determined by solving the following (Equation 1) for the distance between the GNSS satellite and the electronic reference point.

here,
ρ: Distance between GNSS satellite and electronic reference point λ: Wavelength of signal
N: Number of waves to GNSS satellite and electronic reference point (integer value)
φ: Phase of the wave when it reaches the electronic reference point
c: speed of light εt: time error (electronic reference point, GNSS satellite clock error, etc.)
ερ: Spatial error (error due to delay due to ionosphere, troposphere, etc.)
It is.

  The relative positional relationship between the plurality of electronic reference points is calculated by the following (Equation 2) based on the position of each electronic reference point.

here,
P ₁₂ : Distance between electronic reference point 1 and electronic reference point 2
x: x-axis coordinate of the electronic reference point
y: y-axis coordinate of the electronic reference point
z: z-axis coordinate of the electronic reference point

FIG. 4 is a diagram showing a flow of movement determination (S02 in FIG. 3) of the electronic reference point evaluation unit 20.
When the alarm information 400 is used as a trigger to start the distance determination between the electronic reference point and the GNSS satellite (S301), the electronic reference point evaluation unit 20 extracts the electronic reference point installed in the earthquake occurrence area included in the alarm information 400. Then, the distance between the extracted electronic reference point P and the GNSS satellite is calculated (S302).
The electronic reference point evaluation unit 20 stores the distance between each electronic reference point of the plurality of electronic reference points and each GNSS satellite with the identification number stored in the recording unit 50, and is stored in the storage unit 50. The difference between the distance and the distance between the predetermined electronic reference point P calculated at the present time and the GNSS is calculated. Then, the calculated difference is compared with a predetermined threshold value to determine whether or not the difference exceeds the threshold value (S303).
Next, the determination process of S302-S303 is implemented about all the GNSS satellites about the extracted electronic reference point (S304).
In addition, when there are a plurality of electronic reference points extracted as an earthquake occurrence area, the processes of S302 to S304 are performed for each electronic reference point.

  Next, the electronic reference point evaluation unit 20 determines whether or not the threshold value of all the GNSS satellites is exceeded for the electronic reference point determined in S303, using the result of the step S304 (S305).

  As a result of the determination in S305, when the result exceeds the threshold only for some but not all GNSS satellites, the observation data 200 using the GNSS exceeding the threshold is set by the user (GPS receiver T possessed by the user). Processing to exclude from observation data used for positioning is performed (S311). After the exclusion, the process proceeds to step S09 shown in the flowchart of FIG. 3 (S313).

If the threshold value is exceeded for all GNSS satellites as a result of the determination in S305, the electronic reference point evaluation unit 20 determines the relative position between the electronic reference point and an electronic reference point installed around the electronic reference point. Is calculated (S306). Electronic reference points installed in the periphery refer to about 1 to 5 electronic reference points that are close to each other.
The electronic reference point evaluation unit 20 calculates a difference between the relative position calculated in S306 and the immediately preceding relative position (S307). The electronic reference point evaluation unit 20 calculates the relative positional relationship at a predetermined timing and stores it in the recording unit 50.
The electronic reference point evaluation unit 20 performs steps S306 to S307 for all electronic reference points other than the extracted electronic reference point (S308).

Next, the electronic reference point evaluation unit 20 has an electronic reference point whose relative position with respect to the surrounding electronic reference point is shifted before and after the earthquake based on the calculation result of the relative position difference with the surrounding electronic reference point. Whether or not (S309).
For example, when the relative positions of all the surrounding electronic reference points are shifted before and after the earthquake, there is a high possibility that the electronic reference point itself at the center of the surrounding electronic reference points is moving. Further, among the peripheral electronic reference points (peripheral electronic reference points), there is a deviation in the relative positional relationship between the specific peripheral electronic reference point and any electronic reference point. If there is no deviation in the positional relationship, the specific surrounding electronic reference point is likely to have moved due to the earthquake.
As a result of determining whether or not there is an electronic reference point whose relative position is shifted before and after the earthquake (S309), if there is an electronic reference point whose relative position is shifted, the electronic reference point is corrected data. Excluded from the electronic reference points used for generation (S312), the process proceeds to the generation of correction data (S313).
On the other hand, when there is no electronic reference point whose relative position is shifted around the extracted electronic reference point, the extracted electronic reference point is set as an electronic reference point to be corrected (S310). And it transfers to S04 of the flowchart of FIG.

Returning to the flowchart of FIG.
When it is determined in the step S02 of FIG. 3 that the movement of the electronic reference point is caused by the earthquake (S02), the electronic reference point evaluation unit 20 selects the electronic reference point that is the correction target (S03).
Next, a temporary correction range is created for the electronic reference point to be corrected (S04), and temporary correction range correction data is created (S05).

FIG. 5 is a flow for generating a temporary correction range and generating temporary correction range correction data. FIG. 6 is a conceptual diagram for explaining the temporary correction range.
In FIG. 6, P (A) represents an electronic reference point that has been displaced from the initial installation position due to movement of the electronic reference point, and P (B) represents a positional deviation from the initial installation position without movement of the electronic reference point. Represents an electronic reference point where no occurs. 500 is a normal reinforcement information generation range before the occurrence of an earthquake, and 600 is a temporary correction range.

In the flowchart of FIG. 5, when the creation of the temporary correction range 600 is started (S05 in FIG. 3), the electronic reference point selection unit 30 detects an electronic reference point P (A) that has shifted due to movement (S502).
Next, the electronic reference point selection unit 30 searches for the electronic reference point P that exists around the detected electronic reference point P (A), and the closest position is the electronic reference point P (B) that does not move. The electronic reference point P (b) located at is selected (S503).
Steps S502 to S503 are performed on all electronic reference points P (A) where a deviation has occurred (S504).
In this way, the electronic reference point selection unit 30 selects a plurality of electronic reference points P (B) having no movement around the electronic reference point P (A) determined to be moved.
Next, the electronic reference point selection unit 30 creates a temporary correction network using the electronic reference point P (B) without movement selected in S502 to S504 (S505).
The electronic reference point selection unit 30 outputs the numbers assigned to the electronic reference points constituting the temporary correction network to the correction data generation unit 40.

The correction data generation unit 40 creates correction data in the temporary correction range 600 using only the observation data from the selected electronic reference point P (B) without movement (S506).
The temporary correction range 600 includes an installation position of the electronic reference point P (A) determined to be moved, and is a range narrower than the normal correction data generation range 500. FIG. 6 shows an example of the generated temporary correction range 600 and the normal correction data generation range 500.

In this way, the electronic reference point selection unit 30 extracts the electronic reference point P (B) that has not been moved around the electronic reference point P (A) that has been determined to be moved and has been corrected, and the electronic reference point number. Is output to the correction data generation unit 40.
The correction data generation unit 40 creates temporary correction range correction data using the observation data of the electronic reference point P (B) without movement (S05 in FIG. 3).

Next, the electronic reference point position calculation unit 60 recalculates the coordinates of the electronic reference point P (A) determined to be moved (S06 in FIG. 3).
FIG. 7 is a detailed flowchart for recalculating the coordinates of the electronic reference point P (A) determined to have moved.
In FIG. 7, the electronic reference point position calculation unit 60 receives observation data received from the GPS satellite S by the electronic reference point P (A) determined to be moved, and temporary correction range correction data generated by the correction data generation unit 40. The coordinates of the current position of the electronic reference point P (A) determined to be used are calculated (S702).
In this way, the electronic reference point position calculation unit 60 collects the coordinates of the current position of the electronic reference point P (A) for a certain period of time (S703).
When the electronic reference point position calculation unit 60 calculates the coordinates of the current position of the electronic reference point P (A), the correction data generation unit 40 then sets the electronic reference point P (B) constituting the temporary correction network to the electronic reference point P (B). Point P (A) is also added. The correction data generation unit 40 uses the current position of the electronic reference point P (A) and the electronic reference point P (A) obtained by recalculating the coordinates in the position and observation data of the electronic reference point P (B) constituting the temporary correction network. In addition to the observation data received, the correction data in the temporary correction network is newly generated. Then, the electronic reference point position calculation unit 60 calculates the coordinates of the electronic reference point P (A) after the movement using the newly generated correction data (S704).
Steps S703 to S704 are performed until a difference between the coordinates of the electronic reference point P (A) calculated in S704 and the coordinates of the electronic reference point P (A) calculated last time is obtained, and the difference becomes equal to or less than a predetermined threshold. Is repeated (S705).
When the difference is equal to or smaller than the predetermined threshold, the electronic reference point position calculation unit 60 sets the calculated coordinates of the electronic reference point P (A) as the correct coordinates of the electronic reference point P (A) after movement (S706). ).

  Returning to FIG. 3, the electronic reference point position calculation unit 60 resets the coordinates of the electronic reference point P (A) after the movement for all the electronic reference points P (A) determined to be moved (S07). . The correction data generation unit 40 adds the coordinates of the electronic reference point P (A) after the movement and the observation data, and generates new correction data (S08).

  The distribution server 100 subsequently distributes the correction data newly generated in S08 of FIG. 3 to the user via a network or on radio waves from a GNSS satellite or a ground station.

As described above, the correction data distribution server according to the present invention performs the automatic restoration operation even when the electronic reference point is moved due to an earthquake or the like and the stored electronic reference point coordinates are different from the actual coordinates. Thus, the presence or absence of movement of the electronic reference point is automatically confirmed, and if there is a movement, correction data is newly generated based on the position coordinates of the electronic reference point after the movement and the observation information. Distribution can be performed.
As a result, the receiver terminal that receives the correction data, corrects the observation data, and performs positioning can continue to perform high-precision positioning without being affected by the occurrence of an earthquake. A correction data distribution server that always distributes data can be provided.

10 electronic reference point observation data reception unit, 20 electronic reference point evaluation unit, 30 electronic reference point selection unit, 40 correction data generation unit, 50 recording unit, 60 electronic reference point calculation unit, 100 correction data distribution server (distribution server), 110 central center, 120 electronic reference point coordinates determined to move, 210 (210-1, 210-2,..., 210-n) observation data, 300 correction data, 400 alarm information, P (P1, P2,.・, Pn) Electronic reference station, S (S1,..., Sn) GPS satellite, T GPS receiver (positioning receiver terminal) possessed by the user.

Claims (4)

A correction data distribution server that generates and distributes correction data for positioning using reception information received by a plurality of electronic reference points from a satellite of GNSS (Global Navigation Satellite System),
When the installation position of the electronic reference point is moved, an electronic reference point without movement is extracted from the electronic reference points installed around the moved electronic reference point, and the extracted electronic reference point without movement is extracted. Temporary correction data is generated using the position information of the point and the received information received by the electronic reference point without movement, and the post-movement position of the moved electronic reference point is calculated using the temporary correction data. ,
A correction data distribution server that newly generates and distributes correction data using the moved position of the moved electronic reference point and the reception information received by the moved electronic reference point. The correction data distribution server, based on the comparison of the distance between the satellite and the electronic reference point and the comparison of the distance between the electronic reference point and an electronic reference point installed around the electronic reference point, correction data distribution server according to claim 1, wherein the installation position is characterized in that determines whether or not to move. The movement of the electronic reference point is caused by an earthquake, and the correction data distribution server compares the distance between the satellite and the electronic reference point before and after the occurrence of the earthquake, and the electronic reference point and its surroundings. The correction data distribution server according to claim 2 , wherein it is determined whether or not the installation position of the electronic reference point has moved based on a comparison of distances between the electronic reference point and the electronic reference point. The correction data distribution server, in the electronic reference points placed around the electronic reference point has moved, according to claim 1, wherein extracting the electronic reference point without moving in the closest position Correction data distribution server.

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