SIGéo CEREGE
CRX is a Hatanaka compression for Rinex file used by many permanent networks. Y. Hatanaka of GSI wrote softwares for compress/uncompress, see https://terras.gsi.go.jp/ja/crx2rnx.html.
To use the software (example of CRX compression to uncompressed RNX format):
dataset :
photos with timestamps
UBX from M2 and from base station
Processing:
1- Post-Process base station and get corrected coordinates
2- with Emlid Studio (or RTKLib) calculate events (triggers) positions from UBX
as output one gets an …._events.pos file that gives corrected coordinates for each event together with a timestamp
3- extract timestamps from exif of pictures
use exiftool with this command
exiftool -n -csv -filemodifydate -api TimeZone=UTC *.JPG > metadata.csv
the output file “metadata.csv” gives the name of the picture and the timestamp in UTC format
4- Merge …_events.pos and pictures events
For now I’ve got this ugly Python script:
#! /usr/bin/env python
"""
Update Emlid Reach Survey points with PPK position output from RTKLIB
David Shean
dshean@gmail.com
Edited to fix Pandas datetime/Timestamp tz issues, and a few key changes likely based on Emlid updates
"""
import os
import argparse
import numpy as np
import pandas as pd
def getparser():
parser = argparse.ArgumentParser(description='Update Emlid Reach Survey points with \
PPK positions from RTKLIB')
parser.add_argument('survey_pts_csv_fn', type=str, help='Survey point csv filename')
parser.add_argument('ppk_pos_fn', type=str, help='PPK pos filename')
return parser
def main():
parser = getparser()
args = parser.parse_args()
survey_pts_csv_fn = args.survey_pts_csv_fn
ppk_pos_fn = args.ppk_pos_fn
print('Loading: %s' % survey_pts_csv_fn)
survey_pts = pd.read_csv(survey_pts_csv_fn, parse_dates=[1], header=0)
survey_pts['date']=pd.to_datetime(survey_pts['FileModifyDate'],format="%Y:%m:%d %H:%M:%S+00:00")
survey_pts.sort_values('date', inplace=True)
survey_pts.index=survey_pts['date']
print(survey_pts.dtypes)
print(survey_pts)
header = 'Date UTC latitude(deg) longitude(deg) height(m) Q ns sdn(m) sde(m) sdu(m) sdne(m) sdeu(m) sdun(m) age(s) ratio'
print('Loading: %s' % ppk_pos_fn)
ppk_pos = pd.read_csv(ppk_pos_fn, comment='%', delim_whitespace=True, names=header.split(), parse_dates=[[0,1]])
ppk_pos['date']=pd.to_datetime(ppk_pos['Date_UTC'])
ppk_pos.index=ppk_pos['Date_UTC']
print(ppk_pos.dtypes)
print(ppk_pos)
# Applying merge_asof on data and store it
# in a variable
merged_dataframe = pd.merge_asof(ppk_pos, survey_pts, right_index=True,left_index=True,direction='nearest',tolerance=pd.Timedelta("1s"))
print(merged_dataframe)
#Write out new file
out_fn = os.path.splitext(survey_pts_csv_fn)[0]+'_merged.csv'
print("Writing out: %s" % out_fn)
merged_dataframe.to_csv(out_fn)
if __name__ == "__main__":
main()5- In Metashape, import the coordinates of the cameras from the new file
GPS time system (recording the absolute number of seconds since the start of the GPS epoch at midnight on January 6th 1980)
Sometimes GPS time is given with an offset (e.g. 1000000000), in this case the 0 value corresponds to 2011/09/14 at 01:46:25 UTC.
Note also that POSIX (Unix) time is given since Jan 1st, 1970, 00:00:00 UTC.
835734.87 6250812.50 -3.04 20 0 57560982
example of gps dataset
835734.88 6250296.85 -8.16 30 0 46351553
835734.88 6250476.48 -6.97 30 0 57559145
The gps epoch is in the sixth field, and the values are offset by 1 billion. To convert to date one can use Python.
>>> import datetime
>>> datetime.date.fromtimestamp(1315964785) #posix time of the GPS epoch including the 1 billion offset
datetime.date(2011, 9, 14)
>>> datetime.date.fromtimestamp(1315964782+57560982) # gps time of the dataset + the posix time
datetime.date(2013, 7, 11)Clear introduction about Global and local referential (Lantmateriet) : “Positions determined by the GNSS method Precise Point Positioning (PPP) are in the same reference frame as the orbits, i.e. usually a realization of ITRS, e.g. ITRFyy, IGSyy or WGS84, where “yy” represents the year of the realization. The coordinates change with time in the ITRS realizations, because of the plate tectonics. Hence,the determined coordinates are given in the epoch of the observations. For practical applications like mapping and referencing spatial data , a static system/frame, which does not change with time, is desired. For this purpose, ETRS89 has been developed for Europe. ETRS89 coincides with ITRS at epoch 1989.0.”
Another simple reading about dealing with ITRS, ETRS and WGS84 is at Confluence website.
Nota : the transformations made by GIS software from WGS84 to local referential are precise at 1 meter only. For centimeter accuracy, use a geodetic software taking into account the velocities of the ITRF referential relative to the local referential (e.g. ETRF for Europe).
There are many WGS84 realizations. The latest compares with ITRF08 and ITRF14, see table below:
| Year | Realization (Epoch) | For all practical purposes equivalent to: |
|---|---|---|
| 1987 | WGS 1984 (ORIG) | NAD83 (1986) |
| 1994 | WGS84 (G730) | ITRF91/92 |
| 1997 | WGS84 (G873) | ITRF94/96 |
| 2002 | WGS84 (G1150) | ITRF00 |
| 2012 | WGS (G1674) | ITRF08 |
| 2013 | WGS (G1762) | Compares to ITFR08 within 1cm Root Mean Square (RMS) overall |
For US, WGS84 (G1762) is equivalent at 1cm to ITRF14. For France also ITRF14 ~ ITRF08 at less than 1cm, the transformation is given here http://itrf.ensg.ign.fr/trans_para.php
For France, the official referential is RGF93, which in its latest version is defined as ETRF2000 (epoch 2009.0) ( https://geodesie.ign.fr/index.php?page=rgf93 ).
Position and velocities of the IGS stations in ITRF2014 at epoch 2010 is given at this adress http://itrf.ensg.eu/ITRF_solutions/2014/doc/ITRF2014_GNSS.SSC.txt
also at https://itrf.ign.fr/ITRF_solutions/2014/doc/ITRF2014_GNSS.SSC.txt
Reference online tool to convert between ITRF and ETRF : http://www.epncb.oma.be/_productsservices/coord_trans/index.php
Coordinate transformation software for France : Circé IGN
Coordinate transformation software : PROJ
We have made a GNSS survey in May 2020 that we want to convert to France official referential in a projection. The GNSS referential will then be ITRF14 (epoch 2020.1), and the French referential will be RGF93 with the associated projection Lambert93. In order to do so, we need to make some referential transformation, and also some conversion between cartesian coordinates, geographic coordinates and projected coordinates.
To transform ITRF14 (epoch 2020.1) to RGF93, use this site and choose ETRF2000 (epoch 2009) as equivalent to RGF93 (see this post), for the velocities you must choose the one of the nearest IGS station (positions and velocities given at ITRF official site or there or Euref site). Then to transform cartesian to geographic coordinates, use Circé IGN software. And finally, use also Circé to convert to projected coordinate system.
The main methods of GNSS processing are (1) the classical differential correction with a permanent base station, and (2) the Precise Point Positionning (PPP) method that does not require a base station and uses precises clock and ephemeris data.
The tools used can be softwares or web-services. Among software we can distinguish between commercial softwares (e.g. Trimble Business Center TBC), open-source softwares (e.g. RTKLib), and scientific softwares (Bernese, Gamit/Globk). We will introduce RTKLib and web-services.
RTKLib is the main open-source library and software to process GNSS data. It can do conversion, post-processing, navigation, plotting, and so on.
Note : Several versions of the software exist and they behave somewhat differently. I’ll try to describe them one by one but you’d better check carefully your results compared to another “official” reference in order to validate your process.
Versions of RTKLib :
Complementary tools for dealing with POS files from RTKLib and CSV files from ReachView :
This processing is done with static GNSS correction using a network of permanent stations.
RGP IGN http://rgp.ign.fr/SERVICES/calcul_online.php , good for France, gives results in many coordinate systems including RGF93-Lambert93
GPS and Glonass ephemeris data, along with atmospheric data at https://kb.igs.org/hc/en-us/articles/115003935351
and also here (search more simple) https://webigs.ign.fr/gdc/fr/product/format#ephem
and also here (search simple too) https://cddis.nasa.gov/Data_and_Derived_Products/GNSS/orbit_products.html
IGS Antenna calibration file (does not contain Emlid Reach RS2) : igs14.atx
List of IGS stations : here
GPS Calendar to get the GPS week : here or at IGN site
Julian calendar to get GPS day : here or at IGN site
Offset between GPST (GPS Time) and UTC : here
A utility tool by Trimble can be used to convert raw files T02 from Trimble devices to standard Rinex format: download from https://www.trimble.com/support_trl.aspx?Nav=Collection-40773&pt=Trimble%20RINEX
Make sure to install first the Trimble Configuration Utility
Cette procédure traite de la correction différentielle des associés au fichier SSF, acquis avec des appareils Trimble Juno SB, équipés des logiciels ArcPad8 et GPSCorrect.
0.Le fichier SSF ne contient que des positions et non de l’information attributaire. Les informations attributaires sont contenues dans les fichiers SHP ou les AXF.
Pour réaliser la correction différentielle, vous devrez corriger le fichier SSF et ensuite réaliser la synchronisation entre le fichier corrigé COR et le fichier SHP ou AXF.
1. Copier les données de votre PAD (ex. Trimble Juno SB) sur le poste local. Mettre le fichier .ssf et les shapefiles dans un même répertoire.
2. Pour effectuer la correction différentielle, la méthode est d’utiliser l’assistant de correction de GPS Pathfinder Office disponible par le menu “Outils/Correction différentielle”. Vous obtenez alors un fichier GPSCorrect.cor.
A noter dans cet assistant, l’importance d’inclure dans le fichier “Cor” à la fois les positions corrigées et non corrigées (paramètres disponibles dans l’assistant, à la fenêtre “Paramètres de correction”, en cliquant sur “Changer”, dans l’onglet “Sortir”). Ce paramètre permet d’obtenir une correspondance exact entre le fichier SSF et le fichier COR.
3. Avant de procéder à la synchonisation, assurez-vous que les fichiers SHP (DBF, SHX….ou AXF seul) se trouvent dans un répertoire spécifique, dans lequel se trouvent également les fichiers SSF et COR….
4. Aller ensuite dans le dossier “Outils/Autre/ShapeCorrect” afin de lancer l’assistant de synchronisation.
6. Dans “ShapeCorrect”, cliquer sur “Parcourir” afin de sélectionner les fichiers SHP (ou le fichier AXF). Il n’est pas nécessaire de sélectionner les fichiers SSF et/ou COR, mais ils se doivent d’être présents dans le meme répertoire.
7. C’est à vous de décider si vous souhaitez dans les fichiers résultants les positions corrigées et/ou non corrigées.
8. Cliquer sur “OK” afin de lancer la synchro. Vérifiez le résultat de la synchronisation.