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)
On peut télécharger les données acquises par le tachéomètre Lecia TCR 805 avec le logiciel Leica Geo Office. Ce logiciel ne s’installe que sur Windows 7. L’installation sur Windows 10 n’aboutit pas. Le logiciel se trouve ici: \\geomorpho\Logiciel\leica\Leica Geo Office Tools_fr.zip Le téléchargement des données est très simple avec un câble série(pas d’installation de driver requise). Elle peut poser des problèmes avec un cable USB.
Pour le cable USB, le driver s’installe tout seul (validé sur Windows 7). Ensuite utiliser l “Data Exchange Manager”, il faut sur le port COM correspondant configurer les paramètres avec l’instrument TPS800 et le taux de transfert 19200 baud. Les autres paramètres peuvent être laissés par défaut.
Ensuite dans la fenêtre de transfert des données, il suffit de faire glisser les fichiers, et choisir le format IDX.
Windows 10
Avec le cable USB, le driver s’installe tout seul (validé sur Windows 7 et aussi sous Windows 10). Ensuite utiliser en tant qu’Administrateur le logiciel “Data Exchange Manager”, il faut sur le port COM correspondant configurer les paramètres avec l’instrument TPS800 et le taux de transfert 19200 baud. Les autres paramètres peuvent être laissés par défaut.
Ensuite dans la fenêtre de transfert des données, il suffit de faire glisser les fichiers, et choisir le format IDX.
PROJ is a generic coordinate transformation software that transforms geospatial coordinates from one coordinate reference system (CRS) to another. It is currently used in many GIS softwares, but can also be used through an API or by command-line tools.
Below some usefull command lines:
Simple conversion from a known coordinate system (CS) to another known CS :
More documentation https://proj.org/usage/quickstart.html
to add some formatting to output, specify the format with “-f” as a printf format string. For example “-f %.8f” will return the coordinate in decimal degrees with 8 decimals
13.26727481 42.22309481 0.00000000
to input several coordinates at a time, either use a file and pipe with cat
cat coords_utm.txt | cs2cs +init=epsg:32633 +to +init=epsg:4326 -f %.8f
Should return the list of converted coordinates
13.26727481 42.22309481 0.00000000
13.54977927 42.05589846 0.00000000
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
Example : converting from ITRFxx (epoch XXXX) to RGF93
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
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 :
Official software, with actual version 2.4.2. Does not work for me in post-processing as it is not possible to load base station Rinex data.
Emlid Fork here. Should be best for conversion of UBX (Emlid raw format) to Rinex. For what I can say, it worked for conversions, for post-processing of the base station, but it was not stable for post-processing of rover.
RTKLib_Explorer fork here. Located on the really rich blog about GNSS and RTKLib named RTKLibExplorer, this tool works well and is well documented. The setting of parameters for static processing and obtain a single position is hard (set ON for “Output Single for Sol outage” and set a value for Max Sol Std)
Complementary tools for dealing with POS files from RTKLib and CSV files from ReachView :
La connexion directe de certains GPS et périphériques (Juno, GeoXT, TSC3, …) sous Windows 10 ne fonctionne pas, il faut installer un gestionnaire PC de Windows Mobile
puis un patch correctif Windows 10
L’ensemble est disponible sur le serveur geomorpho/logiciels/terrasync/correctif_windows_mobile , ou au support technique de D3E
Pour les Juno Trimble : si l’installation des correctifs n’est pas suffisante, alors aller dans le menu du Juno Windows/Paramètres/Connexions/USBversPC et cocher (ou décocher) la case “Activer la fonctionnalité de reseau avancée”, puis attendre quelques secondes la connexion
On pourra consulter la procédure de Geomesure également
