§ 009. PPK post-processing of static files by TOPAZ

# Intro

Imagine there is need to post-proces GNSS observables (raw data) from base and static rover. For instance, 'static rover' will be used further as base for local RTK. Thus we need to known precise coordinates of this base.

# Input Data

To be concrete, let's consider we need to process observations from ASIR00ITA and M0SE00ITA permanent stations located in Italy, Roma. Date: 01-October-2023.

These files are in Hatanaka compressed form (CRX), 24h, 30 sec sampling rate:

ASIR00ITA_R_20232740000_01D_30S_MO.crx

M0SE00ITA_R_20232740000_01D_30S_MO.crx

# What is TOPAZ?

TOPAZ is KernelSAT PPK post-processing engine and online service. It allows to compute precise rover positions (both static and kinematic) using base and rover measurements.

The engine re-process data many times w/ different settings and assumptions including backward processing. Combination of multiple runs results in more accurate and reliable solutions w/ extended FIX availability.

# Run TOPAZ

Open TOPAZ uploading page. Let's ASIR00ITA station be a rover, M0SE00ITA - base.

TOPAZ may process CRX files (Compact RINEX) w/o need to convert them into RINEX in advance. Lack of CRX support might be quite annoying since many of CORS networks (especially public) stores and provides data in CRX format.

TOPAZ service doesn't worry you about Ephemeris file. TOPAZ does pre-analysis of uploaded rover & base observables and 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).

# TOPAZ Results

Once TOPAZ is finished, we will see detais about base and rover data, RTK statistic, interative plots w/ positions and epoch-by-epoch positions in form of CSV or NMEA GGA message.

System parameters

Next table reminds us who was the base and rover:

Input files

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

3.03
Hatanaka Compressed (CRX)

3.03
Hatanaka Compressed (CRX)

Date: 2023.10.01
Time: 00:00:0.00
DOY:  274
Week: 2282

Date: 2023.10.01
Time: 00:00:0.00
DOY:  274
Week: 2282

Date: 2023.10.01
Time: 23:59:30.00
DOY:  274
Week: 2282

Date: 2023.10.01
Time: 23:59:30.00
DOY:  274
Week: 2282

LEIAR20         NONE

LEIAR25.R4      LEIT

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

Post-Processing Settings

X:  4642432.76
Y:  1028629.1744
Z:  4236854.0159

Interactive Map shows base and average rover position.

Horizontal positions (UTM) are showed on the next interactive plot. Average is substracted. 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.

Next plot presents Geodetic altitude. May be zoomed as well.

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 observables PPK post-processing was considered. TOPAZ online service was used. It is able to process Compact RINEX files as well as standard RINEX of versions 2,3 and 4. 24h of data with 30 sec sampling rate were processed. TOPAZ does not require ephemeris file be provided by a user. TOPAZ downloads ephemeris automatically. 100% availability of FIX achieved in this concrete case what is expected since not too long base line and open-sky conditions. Positions may be saved for post-analysis and further use in form of CSV file or NMEA GGA message.