§ 010. GNSS post-processing of kinematic files by TOPAZ

# Intro

Let's consider practical use-case - there is need to post-process GNSS observables (raw data) from kinematic rover. TOPAZ online post-processing service is considered to be used.

# Input Data

Concrete data set was collected by Alessio Bonfante and shared in EMLID forum post. We will use these data in this example since Alessio kindly allowed it.

To be concrete, data set name is Reach_20240202140255-TOPCON-1. Rover file was collected on EMLID Reach RS3 receiver in UBLOX UBX format. Corrections from base - Network RTCM3 VRS (Virtual Reference Station):

Reach_raw_20240202140255.UBX

Reach_base_20240202140255.RTCM3

Original raw data may be found here: KSAT010_OriginalData.zip

# What TOPAZ is?

TOPAZ is post-processing online service. It allows to compute precise rover positions using base and rover measurements.

TOPAZ process the data with different internal settings and ambiguity resolution assumptions. Combination of multiple runs results in more accurate and reliable solutions w/ extended FIX availability.

# Convert UBLOX UBX to RINEX

Since rover measurements are presented in UBLOX UBX format and TOPAZ requires RINEX, let's convert UBX to RINEX with help of RTools service.

Once converting is done, download result RINEX file. Rename it to rover.o24 for clarity.

# Convert RTCM3 to RINEX

RTools service will be used as well for converting RTCM3 corrections to RINEX. Data were collected on 02-Feb-2024. Date will be needed further for restoring full date+time epoch stamp in RINEX file.

Once converting is done, download result RINEX file. Rename it to base.o24 for clarity.

Converted RINEX files (both base and rover) may be found here: KSAT010_RINEX.zip

# Run TOPAZ

It is time to run TOPAZ post-processing. Open TOPAZ uploading page and load base and rover RINEX files.

TOPAZ service doesn't worry you about Ephemeris file. TOPAZ automatically downloads required ephemeris. Next, let's check post-processing settings. Base coordinates will be taken from RINEX file by default. Otherwise one may specify concrete geocentric XYZ coordinates of base antenna ARP (Antenna Reference Point). Elevation mask may be kept by default (15^o).

Next, enter security code, press Upload button and wait a little bit till TOPAZ process the data.

# TOPAZ Results

First table informs about Request ID. Using this ID one may contact KernelSAT team to check the data and answer questions related to this concrete processing session.

System parameters

Here we may see detailed information about base and rover files:

General Info

3.05

3.05

Date: 2024.02.02
Time: 14:03:13.90
DOY:  33
Week: 2299

Date: 2024.02.02
Time: 14:03:14.00
DOY:  33
Week: 2299

Date: 2024.02.02
Time: 14:11:1.80
DOY:  33
Week: 2299

Date: 2024.02.02
Time: 14:11:1.00
DOY:  33
Week: 2299

-Unknown-

ADVNULLANTENNA

Post-processing settings as well as statistic of RTK position types are presented further.

Post-Processing Settings

X:  4359003.8326
Y:  851510.636
Z:  4562632.674

Interactive Map shows base and average rover position.

Horizontal positions (UTM) are showed on the next interactive plot. Average is subtracted. Absolute coordinates as well as baseline components may be found in GGA / CSV files below.

Plot may be zoomed. Select the area of interests by pressed left mouse button. Right mouse button click returns original zoom.

Finally, reckoned positions (epoch-by-epoch) are presented in CSV text form and NMEA GGA message for further analysis and use.

CSV file include TAB separated columns. Columns description is presented below.

# Column Name       Description
#  0      Epoch_ID   Epoch identificator
#  1      Date       GPS Time Date, YMD format
#  2      Time_hms   GPS Time (hms) within day
#  3      Time_ms    GPS Time [ms] within day
#  4      POS_TYPE   Position Type (4 - FIXED, 5 - FLOAT)
#  5      SV_USED    Number of SVs used in RTK solution
#  6      BL_X       X-component of Base-Rover ARP baseline, m
#  7      BL_Y       Y-component
#  8      BL_Z       Z-component
#  9      X          X-coordinate of rover ARP, m
# 10      Y          Y-coordinate
# 11      Z          Z-coordinate
# 12      LAT        Geodetic Latitude of rover ARP, deg
# 13      LON        Longitude, deg
# 14      ALT        Altitude, m
# 15      PDOP       Position DOP

# Summary

Example of GNSS kinematic observables post-processing by TOPAZ service is presented. Despite challenging VRS corrections, almost 100% FIX was achieved. Positions may be saved for post-analysis and further use in form of CSV file or NMEA GGA message.