MATCHEDPOS

Matched RTK position

Platform:

OEM719, OEM729, OEM7500, OEM7600, OEM7700, OEM7720, PwrPak7, CPT7, CPT7700, SMART7

This log represents positions that have been computed from time matched base and rover observations. There is no base extrapolation error on these positions because they are based on buffered measurements, that is, they lag real time by some amount depending on the latency of the data link. If the rover receiver has not been enabled to accept RTK differential data or is not actually receiving data leading to a valid solution, this is shown in fields #2 (sol status) and #3 (pos type).

This log provides the best accuracy in static operation. For lower latency in kinematic operation, see the RTKPOS log or BESTPOS log. The data in the logs changes only when a base observation (RTCMv3) changes.

A good message trigger for this log is onchanged. Then, only positions related to unique base station messages are produced and the existence of this log indicates a successful link to the base.

Asynchronous logs, such as MATCHEDPOS, should only be logged ONCHANGED otherwise the most current data is not output when it is available. This is especially true of the ONTIME trigger, which may cause inaccurate time tags to result.

The RTK system in the receiver provides two kinds of position solutions. The Matched RTK position is computed with buffered observations, so there is no error due to the extrapolation of base station measurements. This provides the highest accuracy solution possible at the expense of some latency which is affected primarily by the speed of the differential data link. The MATCHEDPOS log contains the matched RTK solution and can be generated for each processed set of base station observations.

The Low-Latency RTK position is computed from the latest local observations and extrapolated base station observations. This supplies a valid RTK position with the lowest latency possible at the expense of some accuracy. The degradation in accuracy is reflected in the standard deviation and is summarized in An Introduction to GNSS available on our website at novatel.com/an-introduction-to-gnss. The amount of time that the base station observations are extrapolated is in the "differential age" field of the position log. The Low-Latency RTK system extrapolates for 60 seconds. The RTKPOS log contains the Low-Latency RTK position when valid, and an "invalid" status when a Low-Latency RTK solution could not be computed. The BESTPOS log contains either the low-latency RTK, PPP or pseudorange-based position, whichever has the smallest standard deviation.

Message ID: 96

Log Type: Asynch

Recommended Input:

log matchedposa onchanged

ASCII Example:

#MATCHEDPOSA,COM1,0,63.0,FINESTEERING,1419,340034.000,02000040,2f06,2724;
SOL_COMPUTED,NARROW_INT,51.11635908660,-114.03833102484,1063.8400,-16.2712,
WGS84,0.0140,0.0075,0.0174,"AAAA",0.000,0.000,12,12,12,12,0,01,0,33*feac3a3a

Measurement precision is different from the position computation precision. Measurement precision is a value that shows how accurately the actual code or carrier phase is measured by the GNSS receiver. Position precision is a value that shows the accuracy of the position computation made from the code and/or carrier phase measurements. The P-code L2 measurement precision is not as good as the C/A measurement precision because the NovAtel GNSS receiver is a civilian grade GPS device and does not have direct access to the decrypted military L2 P(Y) code. This means that NovAtel’s semi-codeless P-code L2 measurements are noisier than the civilian band C/A code measurements. Refer to Technical Specifications for the technical specification of the receiver.

Field

Field type

Description

Format

Binary Bytes

Binary Offset

1

MATCHEDPOS header

Log header. See Messages for more information.

 

H

0

2

sol status

Solution status (see Table: Solution Status)

Enum

4

H

3

pos type

Position type (see Table: Position or Velocity Type)

Enum

4

H+4

4

lat

Latitude (degrees)

Double

8

H+8

5

lon

Longitude (degrees)

Double

8

H+16

6

hgt

Height above mean sea level (m)

Double

8

H+24

7

undulation

Undulation - the relationship between the geoid and the WGS84 ellipsoid (m)

When using a datum other than WGS84, the undulation value also includes the vertical shift due to differences between the datum in use and WGS84.

Float

4

H+32

8

datum id#

Datum ID number

61 = WGS84

63 = USER

Enum

4

H+36

9

lat σ

Latitude standard deviation (m)

Float

4

H+40

10

lon σ

Longitude standard deviation (m)

Float

4

H+44

11

hgt σ

Height standard deviation (m)

Float

4

H+48

12

stn id

Base station ID

Char[4]

4

H+52

13

Reserved

Float

4

H+56

14

Float

4

H+60

15

#SVs

Number of satellites tracked

Uchar

1

H+64

16

#solnSVs

Number of satellites used in solution

Uchar

1

H+65

17

#ggL1

Number of satellites with L1/E1/B1 signals used in solution

Uchar

1

H+66

18

#solnMultiSVs

Number of satellites with multi-frequency signals used in solution

Uchar

1

H+67

19

Reserved

Hex

1

H+68

20

ext sol stat

Extended solution status (see Table: Extended Solution Status)

Hex

1

H+69

21

Galileo and BeiDou sig mask

Galileo and BeiDou signals used mask (see Table: Galileo and BeiDou Signal-Used Mask)

Hex

1

H+70

22

GPS and GLONASS sig mask

GPS and GLONASS signals used mask (see Table: GPS and GLONASS Signal-Used Mask)

Hex

1

H+71

23

xxxx

32-bit CRC (ASCII and Binary only)

Hex

4

H+72

24

[CR][LF]

Sentence terminator (ASCII only)

-

-

-