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NTRIP statistics

The NTRIP statistics file allows the user to evaluate the performance of the received RTCM3 messages, including the available message types for the selected NTRIP caster, delays in communication, GNSS performance (i.e., GNSS fix quality and signals tracked), and the processing of the RTCM3 messages by each GNSS receiver.

The first row of the NTRIP file presents the delay in the RTCM3 messages received (for all message types), calculated as the difference between the message timestamp and the receive time. The second row presents this same delay but only for one message type (e.g., RTCM3-TYPE1073). For reference, the average message frequency for most NTRIP casters is about 1 Hz (i.e., a delay of 1 second is expected between two messages of the same type under ideal conditions). Similarly, the third row presents the trend between each message's timestamps and received time. Under ideal conditions, the slope of the line should be 1.

Higher delays can be explained mainly by three factors:

  • The selected NTRIP caster is far from the rover (e.g., further than 40km).

  • The sensor is experiencing constant Internet outages.

  • The Internet connection is slow, causing delays in downloading the corresponding messages.

Small inconsistencies in the delay between RTCM3 messages are expected. However, if there is constantly a delay higher than 2 seconds, then it is worth investigating.

image-20240109-144138.png

RTCM3 message delay.

The fourth row presents the RTM3 message types received by the sensor. In this example, the received RTCM3 messages were:

  • RTCM type 1005: Stationary RTK reference station ARP.

  • RTCM type 1074: GPS MSM4.

  • RTCM type 1087: GLONASS MSM7.

  • RTCM type 1094: Galileo MSM4.

  • RTCM type 1124: BeiDou MSM4.

  • RTCM type 1230: GLONASS code-phase biases.

As shown in the figure, this particular NTRIP caster is streaming one RTCM3 message type per satellite constellation in addition to the reference position of the base station. Therefore, with the available RTCM3 messages, the RTK processor can potentially achieve an RTK-fixed condition with information from every satellite constellation.

image-20240109-144521.png

Received RTCM3 message types.

The Vision-RTK2 requires some of the following RTCM3 message types for proper operation:

image-20240109-144822.png

List of required RTCM3 input messages.

The following rows present the GNSS fix type achieved and the number of signals each GNSS receiver tracked, used, and corrected. The latter indicates how many satellite signals are healthy enough (e.g., good quality signal with enough signal power) and contain corresponding RTCM3 messages to be corrected. Suppose RTCM3 messages are received, but no signals are corrected. In that case, it can indicate that the correction data does not contain the necessary RTCM3 messages or the quality of the raw GNSS measurements is not good enough (e.g., due to electromagnetic interference or multipathing).

image-20240109-151304.png

GNSS receiver performance.

For the Fusion engine to initialize, the sensor must achieve an RTK-fixed state on both GNSS receivers. The available GNSS fix types are:

Fix type

Description

Unknown

The receiver has no satellite signals.

No fix

The receiver does not have enough satellite signals.

Dead reckoning

No satellite signals are available, but dead reckoning is enabled.

Time

The receiver has received time information only.

Single 2D

Autonomous GNSS fix with very few available satellite signals.

Single 3D

Autonomous GNSS fix, typically in situations with no correction data or in outages.

Single 3D - DR

Autonomous GNSS fix with dead reckoning.

RTK float

RTK with ambiguities not fully solved.

RTK fixed

RTK with ambiguities fully solved.

Similarly, the last row indicates how many RTCM3 messages were processed by each GNSS receiver. Ideally, the receiver should process most RTCM3 messages, and no messages should display an error.

image-20240109-152827.png

RTCM3 messages processed by each GNSS receiver.


Example HTML:

ntrip_stats.html

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