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In your professional practice, to meet your missions and obligations, you can count on the knowledge, know-how, centimetric precision and repeatability provided by the Orphéon network. The high precision that the GNSS RTK Orphéon network provides to Topography professionals, makes it possible to carry out quality surveys with complete confidence, but also facilitates and simplifies the management of construction sites or interventions in the field. null Positioning accuracy with Orpheon is centimeter for a standard deviation of 1σ:
  • Included between 1 and 2 centimeters in planimetry,
  • Included between 2 and 3 cm in altimetry.

In various theses on “TOPOGRAPHIC WORKS” it is highlighted that the use of a “real-time GPS” is sufficient for the realization of topographic works of precision class 10 cm within the meaning of the decree of September 16, 2003 (Class A), only within the limits of use of the equipment (pay attention to the close environment) and the limit of implementation of survey methods (see our field phase recommendations below).

Download the technical sheet

Referencing and external control of the network

The referencing of the sites and the monitoring of their stability is ensured by the RENAG, National Observatory, implementing and using continuous GPS measurements for scientific purposes such as: measurement of weak crustal deformations, study of the vapor content of atmospheric water, study of oceanic and hydrostatic overload or even study of gravitational movements. Géodata Diffusion is a private partner of RENAG (see the RENAG website)

Stationing procedure

After the final installation of a reference station on a new site or after maintenance, we obtain an initial approximate position of this site by observations over a minimum period of 72 hours. This duration makes it possible to obtain the first coordinates of the site. Then these observations are conducted over a month in order to acquire the time series that will be used to calculate the position using the Bernese GNSS software: high-precision scientific multi-GNSS data processing software developed at the Astronomical Institute of the University of Bern (AIUB). All the sites are referenced in the RGF93 via a “state of the art” procedure from the stations of the RGP (Permanent GNSS Network). We then obtain the position and the precise three-dimensional coordinates of the site which we can then integrate into the network to deliver the correction services.

Self-checking and monitoring

On a daily basis, we monitor 24 hours a day, all year round, the positioning of each of our reference stations using monitoring tools integrated into our correction calculation platforms (Spider and/or TPP). The monitoring of each of the reference stations is then carried out on a regular basis in order to control the stability of the sites. Internal quality control procedures are carried out regularly. In the field, we regularly check and compare the corrections obtained from the network by positioning ourselves with a mobile GNSS receiver, as our customers would do, on known points such as IGN terminals whose three-dimensional coordinates are known with precision.

Automatic alerts

The entire network is monitored 24 hours a day and alerts are sent in real time to our technical support as soon as a movement or shift of a reference station is observed by the system. Our team is then able to intervene to ensure that a constant quality of service is maintained over time.
(Source lettres IGN GEODINFO) The RGF93 is the French Reference:
  1. three-dimensional geocentric
  2. linked to the global ITRS reference system
  3. associated with the IAG GRS 1980 spheroid
  4. having as its prime meridian the International Meridian (or Greenwich Meridian)
  5. having as associated projections the Lambert-93 projection and the CC 9
  6. Zones projections
  7. horizontal accuracy between 1 and 2 cm (compared to global systems)
  8. vertical accuracy between 2 and 5 cm (compared to global systems)
  9. suitable for modern positioning techniques

Since January 2021 :

In 2019 and 2020, IGN carried out the IGS14 reprocessing and cumulation of the Permanent GNSS Networkexternal link. This has led to the release of a new RGF93, named RGF93 V2b, which is aligned with ETRF2000 epoch 2019.0. This replaces in January 2021 the RGF93V2 benchmark, which was directly compatible with the ETRF2000 era 2009.0.

In 2010 :

A first readjustment to the European system took place in 2010, following the re-observation of the base network (RBF) systematically using the Permanent GNSS Network. The published coordinates are then expressed in a version 2 of the RGF93 frame which corresponds to the ETRF2000 at the epoch 2009.0.

Impact:

The impact of this update is mainly reflected on the ellipsoidal heights and, consequently, on the evolution of the elevation conversion surface.

RAF20:

Since the summer of 2021, you can therefore download this new ‘grid’ from the IGN website (https://geodesie.ign.fr) which takes into account both the evolution of the RGF93 benchmark (ETRF2000 ep.2019.0) and the last two ERNIT field campaigns 2019 and 2020 in mainland France. IGN is also trying to improve the model at each occurrence by introducing some minor corrections from reports or redeterminations caused by local tectonic activity. For mainland France, the RAF20 altimetric conversion surface was updated at the end of 2021 to take into account the maintenance operations of the RGF93 reference mark Pour la Corse, la surface de conversion altimétrique RAC09 reste en vigueur.

The RGF93 is the French Reference:
  1. three-dimensional geocentric
  2. linked to the global ITRS reference system
  3. associated with the IAG GRS 1980 spheroid
  4. having as its prime meridian the International Meridian (or Greenwich Meridian)
  5. having as associated projections the Lambert-93 projection and the CC 9
  6. Zones projections
  7. horizontal accuracy between 1 and 2 cm (compared to global systems)
  8. vertical accuracy between 2 and 5 cm (compared to global systems)
  9. suitable for modern positioning techniques
In accordance with the official decree, since 2010 the coordinates published by the Orpheon network are expressed in the new realization of the RGF93. v2 The RGF (French Geodesic Network) is the legal geodetic system in metropolitan France. The RGF is made up of a reference network, the RGP (Permanent Geodesic Network: http://rgp.ign.fr/).
  • RGF93.v1: ETRF2000 solution at date:t0=1993.0
  • RGF93.v2: ETRF2000 solution at date:t0=2009.0
As part of the operation of the services of the Orphéon network, the transition from RGF93v1 to RGF93v2 led to a change in the coordinates of all the stations of the Orphéon network. The IGN had been commissioned in 2010 by Geodata Diffusion to calculate the RGF9.v2 coordinates for the existing Orphéon stations. Today, the coordinates are updated by solutions from the HxGN SmartNet CrossCheck service. The calculations performed by this service use a Bernese solution. This software is used in particular by the IGS CODE analysis center (Center for Orbit Determination in Europe) which participates in the supply of orbitographic products integrated into the ITRF solution. The quality of the coordinates of the Orphéon stations is of the order of a few millimeters. Since September 2018, the coordinates of the stations of the Orphéon network have been calculated by Hxgn SmartNet Crosscheck in the realization of the ITRF2014 epoch 2010.0 In conclusion, the calculations of the platforms operating the Orpheon services must be carried out in the ITRF, but the solutions delivered are expressed in the official RGF93v2
In metropolitan and continental France, the legal geodetic system is RGF93v2 which corresponds to the ETRF2000 system epoch 2009.0. All the coordinates of our stations are defined in this system. The associated ellipsoid is GRS80. The legal projection is the Lambert 93 9 zone conformal conic projection. Each of these zones covers a latitude band of 2°. The titles of the 9 zones are: CC42/CC43/CC44/CC45/CC46/CC47/CC48/CC49/CC50. “CC” for conformal conic followed by the value of the zone’s central parallel. For example, CC48 covers a band in latitude going from parallel 47°N to parallel 49°N. The definition of these 9 zones ensures an overlap of 1° between each zone. The parameters of these projections are: – Origin latitude: 42/43/…/50 depending on the area considered – Automecoic parallel 1: Origin latitude – 0.75° – Automecoic parallel 2: Origin latitude + 0.75° – Prime Meridian: 3°E – Origin coordinates: 1,700,000 E; (1,000,000 x (origin latitude – 41°)) + 200,000 N In terms of altimetry, the legal system is IGN69, a system of normal altitudes. The Ellipsoidal Heights -> Normal Height transformation grid is RAF09. This grid is an improved version of the QGF98 quasi-geoid. This grid is available in ASCII format at: https://geodesie.ign.fr/contenu/fichiers/documentation/grilles/anciennes/RAF18.mnt
The French Antilles now have a legal and precise national coordinate reference system, compatible with the international terrestrial reference system ITRS, ensuring the interoperability of geographical data, in accordance with the INSPIRE directive. The decree of March 5, 2019 formalizes the legal and precise national coordinate reference system for the Antilles, the RGAF09. The RGAF09 (Réseau Géodésique des Antilles Françaises 2009) thus replaces the WGS84-RAAF91, which remains however usable for an overlay period of three years. RGAF09 is a significant improvement over WGS84. Indeed, it had inconsistencies of several centimeters between the islands as well as an offset of about 70 cm with the International Terrestrial Reference System (ITRS).

RGAF09 as standard on the Orphéon network

As of Monday, December 16, 2019 at 06:30 UTC the Orpheon network uses RGAF09

the new official national reference system for the West Indies: the WGS84-RGAF09. The decree of March 5, 2019 formalizes the legal and precise national coordinate reference system for the West Indies, WGS84-RGAF09. With the officialization of the long-awaited RGAF09 and the improvement it presents the Orpheon network has been updated to offer the new official coordinate system for the Antilles.

Directly in RGAF09

The change is direct without user intervention. No modification is therefore necessary for customers using the Orphéon network, as soon as they connect to the network, the coordinates will be expressed directly in the new official reference WGS84-RGAF09.

The RAAF91 – Always Available

However, for more than 10 years the Orpheon network has been working in the national coordinate reference system WGS84-RAAF91 which will therefore remain valid for another 3 years. Professional network users have become accustomed to using Orpheon and have configured their equipment and their work accordingly. We keep this possibility not to suddenly upset the work of many professionals.

Keep the old reference system RRAF91

Some network users may still need to work with the old RRAF91 reference system for a while longer, to complete a job or resume an old survey without having to do any prior conversion.

We thought of them:

We provide you with new mounting points allowing you to work in the old reference system. Reverting to RRAF91 will require setting up your hardware by selecting one of the new mount points that matches your setup.
      • RRAF91_i-MAX_3.0_GG
      • RRAF91_i-MAX_MSM_FULL
      • RRAF91_VRS_3.0_GG
      • RRAF91_VRS_MSM_FULL
      • RRAF91_MAX_3.0_GG
      • RRAF91_FKP_3.0_GG
      • RRAF91_Plus-Pres_3.0_GG
      • RRAF91_Plus-Pres_MSM_FULL
To avoid confusion, note that the names of these new mount points always begin with RRAF91.

Confusions and changes

The coexistence of two coordinate reference systems in parallel leads to some confusion that we too have seen. Some of our customers have recently reported to us an Orphéon RTK real-time and post-processing positioning problem in Guadeloupe related to the use of different coordinate systems in the same project. They were thus able to observe differences of the order of 60 cm. But as soon as the points used in a project are expressed in the same coordinate system, things get back to normal and customers find all the precision of the Orpheon network. Projects must be treated in their entirety in a single coordinate system, without being mixed.

Coordinate transformation:

It is possible to use our online transformation tool or IGN provides the transformation parameters from local systems and WGS84-RRAF to the RGAF09 system as well as a CIRCE tool.

RGAF09 as standard on the Orphéon network

As of Monday, December 16, 2019 at 06:30 UTC the Orpheon network uses RGAF91

the new official national reference system for the West Indies: the WGS84-RGAF09. The decree of March 5, 2019 formalizes the legal and precise national coordinate reference system for the West Indies, WGS84-RGAF09. With the officialization of the long-awaited RGAF09 and the improvement it presents the Orpheon network has been updated to offer the new official coordinate system for the Antilles.

Directly in RGAF91

The change is direct without user intervention. No modification is therefore necessary for customers using the Orphéon network, as soon as they connect to the network, the coordinates will be expressed directly in the new official reference WGS84-RGAF09.

The RAAF91 – Always Available

However, for more than 10 years the Orpheon network has been working in the national coordinate reference system WGS84-RAAF91 which will therefore remain valid for another 3 years. Professional network users have become accustomed to using Orpheon and have configured their equipment and their work accordingly. We keep this possibility not to suddenly upset the work of many professionals.

Keep the old reference system RRAF91

Some network users may still need to work with the old RRAF91 reference system for a while longer, to complete a job or resume an old survey without having to do any prior conversion.

We thought of them:

We provide you with new mounting points allowing you to work in the old reference system. Reverting to RRAF91 will require setting up your hardware by selecting one of the new mount points that matches your setup.
      • RRAF91_i-MAX_3.0_GG
      • RRAF91_i-MAX_MSM_FULL
      • RRAF91_VRS_3.0_GG
      • RRAF91_VRS_MSM_FULL
      • RRAF91_MAX_3.0_GG
      • RRAF91_FKP_3.0_GG
      • RRAF91_Plus-Pres_3.0_GG
      • RRAF91_Plus-Pres_MSM_FULL
To avoid confusion, note that the names of these new mount points always begin with RRAF91.

Switch from RRAF91 to RGAF09?

Coordinate transformation:

It is possible to use our online transformation tool or IGN provides the transformation parameters from local systems and WGS84-RRAF to the RGAF09 system as well as a CIRCE tool. Helmert parameters necessary for the transformation of coordinates expressed in old systems to RGAF09. IGN provides the parameters needed to transform RRAF91 coordinates into RGAF09 and vice versa. It is therefore possible to indirectly link GNSS work carried out in other systems to the RRAF91 reference. The table below lists the values ​​of these parameters. Note in particular the values ​​of the translations between the RRAF91 and the RGAF09 which differ up to 10 m depending on the area concerned. This testifies to the heterogeneity of the inter-island RRAF91.
Zone Martinique Guadeloupe Guadeloupe Martinique Guadeloupe Guadeloupe
Système de départ Fort Desaix Saint-Anne Fort Marigot RRAF91 RRAF91 RRAF91
Système d’arrivée RGAF09 RGAF09 RGAF09 RGAF09 RGAF09 RGAF09
TX (m) 127.744 -471.060 151.613 0.7696 1.2239 14.6642
TY (m) 547.069 -3.212 253.832 -0.8692 2.4156 5.2493
TZ (m) 118.359 -305.843 -429.084 -12.0631 -1.7598 0.1981
RX (arcsec) -3.1116 0.4752 -0.0506 -0.32511 0.03800 -0.06838
RY (arcsec) 4.9509 -0.9978 0.0958 -0.21041 -0.16101 0.09141
RZ (arcsec) -0.8837 0.2069 -0.5974 -0.02390 -0.04925 -0.58131
D (ppm) 14.1012 2.1353 -0.3971 0.2829 0.2387 -0.4067
Tab. Helmert parameters between Martinique/Guadeloupe local systems and RGAF09 and between RRAF91 and RGAF09. These transformation parameters are included in the IGN software Circé (downloadable from the IGN website http://geodesie.ign.fr/index.php?page=circe#titre1)

As a reminder, in order to be able to position itself within a few centimeters, a GPS/GNSS rover must be able to:

  • perform noise-free phase measurements on at least 5 satellites well distributed in space,
  • and receive differential corrections on these same 5 satellites.
Adding 2 constellations of additional Galileo and BeiDou satellites to those of the GPS and Glonass constellation increases the possibility of receiving a sufficient number of signals and of better quality, especially in difficult places. Here are our recommendations, a sort of checklist which makes it possible to ensure the quality of the points recorded (especially in Z) regardless of the number of constellations used.
  • Control of measurement equipment (Firmware version of GNSS equipment, status of the rod, of the bubble, compliant configuration and configuration)
  • Turn on the mobile and stand on a clear point
  • Ensure good internet connection and service stability
  • Connect to real-time correction services
  • Start a first initialization session of 8 minutes without cycle jumps for 6 satellites being a recommended minimum value for the subsequent fixing of integer ambiguities
  • Centre, bubble, check antenna height and stability
  • Perform measurement work while ensuring GNSS measurement conditions: sufficient number of satellites, GDOP < 3 – 4, Signal/Noise ratio SNR > 50 (on L1) or 40 (on L2)
  • Respect sufficiently long point acquisition times according to the situation, the environment and the place
  • In the event of a cut warning by the receiver or in the event of lifting in a place prone to cuts signal (near trees, buildings, etc.), redo an initialization session
  • Reoccupy the first point at the end of the lift
  • Reoccupy the important points at least once after at least 20 minutes (see control sheet)
  • For the most important or difficult to access points, recording of raw data in Rinex for possible online control post-processing
  • Occupation of all known points in coordinates (RBF, NGF) (see check sheet)
You will also find an article published in XYZ on the subject Real-time static positioning by “filtering and averaging NRTK positions”, Lire l’article  This general method of measurement makes it possible to ensure the quality of the points recorded.
In our recommendations for field phase measurement, we recommend the occupation of all known points in coordinates (RBF, NGF). To know these points near your construction site, the IGN provides you with the location of its terminals as well as a wealth of very useful information for the whole of France., Accès au site de l’IGN  (click to open link) null At Geodata Diffusion, we also use these terminals to regularly check that the corrections we deliver through the Orphéon network comply with the specifications we announce.

On October 26, 2018 for example,

We went to the Lorient region (56) to check the corrections of the Orphéon network and check the potential discrepancies between the data from three IGN terminals and the positions obtained in the field (located on the map above). For each of the sites, we have edited the IGN Geodesic sheet and we are taking readings as follows:
  • Start-up of the measurement equipment and first initialization session of at least 8 minutes.
  • Recording of 6 surveys from the 6 mounting points delivered in GG and Full GNSS. Please note that the correct configuration of the hardware is essential and must correspond to each of the protocols linked to the selected mount point. The risk is to obtain distorted results with erroneous positions (especially in Z).
  • Each point is recorded after at least 60 seconds of acquisition. We then make a 30-minute acquisition in natural mode so that we can then perform a control post-processing (Rinex file recording)
  • We check our measurements one last time by recording at least one additional point with a Full GNSS mount point.

Results on the REDENE reference terminal (56)

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The HDOP, a question of geometry

The positioning accuracy of a satellite navigation system (GPS) is affected by mathematical errors related to the geometry of the observable satellites either because of their position and their distribution above the user.

The idea of ​​geometric DOP (GDOP) is to indicate how measurement errors will affect the final state estimate. DOP can be expressed in a number of distinct measures:
  • HDOP – horizontal dilution of precision
  • VDOP – vertical dilution of accuracy
  • PDOP – position (3D) dilution of accuracy
  • TDOP – temporal dilution of accuracy
  • GDOP – geometric dilution of precision

Benchmarks

These values ​​derive mathematically from the positions of the usable satellites. The signal receivers allow the display of these positions (skyplot) as well as the DOP values

Valeur DDP Classement La description
<1 Idéal Niveau de confiance le plus élevé possible à utiliser pour les applications exigeant la plus grande précision possible à tout moment.
1-2 Excellent À ce niveau de confiance, les mesures de position sont considérées comme suffisamment précises pour répondre à toutes les applications, sauf les plus sensibles.
2-5 Bien Représente un niveau qui marque le minimum approprié pour prendre des décisions précises. Les mesures de position pourraient être utilisées pour faire des suggestions de navigation fiables à l’utilisateur.
5-10 Modérer Les mesures de position pourraient être utilisées pour les calculs, mais la qualité de la correction pourrait encore être améliorée. Une vue plus dégagée du ciel est recommandée.
10-20 Équitable Représente un niveau de confiance faible. Les mesures de position doivent être ignorées ou utilisées uniquement pour indiquer une estimation très approximative de l’emplacement actuel.
>20 Pauvre À ce niveau, les mesures sont imprécises jusqu’à 300 mètres avec un appareil précis de 6 mètres (50 DOP × 6 mètres) et doivent être rejetées.

Sky map

Example of observation of the sky of the GPS and Glonass constellations with a cut-off angle of 45° compared to the sky map in Full GNSS with a cut-off angle of 10°

In case of wrong choice of mounting point:

If the mounting point that you have configured in your equipment does not correspond with the operating mode that you have configured in your equipment either:
  • You will not be able to connect to our servers and therefore you will not be able to obtain a correction. You will therefore not have the expected precision. Your position will remain in natural or floating mode (without correction) the material failing to fix the ambiguities. On the Smartphone application, the symbol locating your equipment will be in red.
  • You will manage to connect to our servers but the corrections you get will be misinterpreted by your equipment. You will therefore not have the expected precision. On the Smartphone application, your position will apparently be fixed (with correction), the symbol locating your equipment will be in green.
It is therefore essential that the configuration of your equipment is checked to match the correction mode expected and configured on your mobile with the corrections delivered by our servers according to the mounting point you have selected. If you change the mounting point, check that you have also adapted the configuration of your equipment so that the 2 correspond well.

Self-check recommendations

In our recommendations for field phase measurement, we recommend the occupation of all known points in coordinates (RBF, NGF). To know these points near your site, the IGN provides you with the location of its terminals as well as a wealth of very useful information for the whole of France, Accès au site de l’IGN  (click to open link) null
  • Control of measurement equipment (Firmware version of GNSS equipment, status of the rod, of the bubble, compliant configuration and configuration)
  • Turn on the mobile and stand on a clear point
  • Ensure good internet connection and service stability
  • Connect to real-time correction services
  • Start a first initialization session (8 minutes without cycle jumps for 6 satellites being one fairly widespread minimum recommended value) for subsequent fixing of integer ambiguities
  • Centre, bubble, check antenna height and stability
  • Perform measurement work while ensuring GNSS measurement conditions: sufficient number of satellites, GDOP < 3 – 4, SNR > 50 (on L1) or 40 (on L2)