Here is what you need to know to use the VRS service of the RinexLab.

Quick overview

To use the VRS service, click VRS in the main menu after you logged in. This will open the VRS generation form. Name your survey, select the datum in which you want to generate the virtual station. Then add up to 4 VRS to be processed in the same survey. For each VRS, indicate the name of the station, the start and end time of the virtual session, the rate at which raw observations are recorded, and the position of the station.

Datum

Select here the datum in which the coordinates of the virtual stations of this survey will be expressed. The possible choices are ETRF2000, RGF93, NAD83, SIRGAS-CON, ETRF2014, RGR92, and ITRF2014. WGS84 is not offered because this datum is not compatible with precision positioning applications. If you are absolutely looking for a virtual station in this datum, it is likely that the definition of your project is incorrect. You can contact us for more information.

Start and end time of the virtual session

These are the start and end dates and times of the RINEX file that will be generated, expressed in GPS time. As a reminder, GPS time corresponds to UTC time with an offset of a few seconds. These seconds are called leap seconds. There are currently 18 leap seconds, which means that a time in GPS time is obtained by the formula [GPS time] = [UTC time] - 18 seconds. You can thus deduce the exact offset between your local time and GPS time if you know your offset to UTC time. However, to define the start and end of a virtual session to the nearest minute, you do not need to be accurate to the nearest second and can simply enter the UTC times of your virtual session in these fields.

Rate

The rates offered are 1 Hz, 2 Hz, 5 Hz and 10 Hz. The selected value indicates the frequency of observations present in the RINEX file. At 1 Hz, there will be 1 set of satellite observations per second, and more precisely, every second round. At 2 Hz, there will be 2, i.e. one per second round, and one per second + 5/10 of a second. And the same reasoning for 5 and 10 Hz. 1 Hz is more than enough for static use. 1 Hz is often sufficient for most kinematic uses coupled with an inertial unit. If you wish to secure the data volume, choose 5 Hz. 10 Hz is rather reserved for specific cases of high technicality.

Position

Define here the position of the virtual station using the marker on the map. In most cases, the position does not need to be very precise. Simply place the station in the immediate vicinity of your working site. You can do a rough search first by using the search field above the map. Enter a city or location and click on the Search location button. This positions the marker on the best search result. You can then zoom in with the zoom buttons to fine-tune the position of the marker. If you really need to position the station very precisely, you can directly enter the latitude and longitude coordinates in the field below the map. Remember that the coordinates are expressed in the datum defined in the survey.

Add a VRS to the survey

To add a VRS, click on the plus sign to the right of the grid. You'll be notified if you try to add more than 4 VRS.

Start the process

You must be the owner of a valid VRS token with a positive number of credits to start the processing. Once the survey has been created, you cannot modify it or add stations. The processing will start automatically.

RINEX output

The RINEX of the virtual station is provided at the end of processing in a ZIP archive containing the observation file with a .obs extension, the ephemeris file with a .nav extension, the ATX file of the antenna of the virtual station, and a JSON file containing the metadata of the virtual session. Obs and nav files are in RINEX 2.11 format. They can contain the 4 constellations GPS, GLONASS, Galileo and BeiDou if the permanent stations used in the processing track all these systems.

The metadata file

The metadata file gathers the name of the station, start and end time of the observations session, antenna and receiver types, antenna height, observation rate. APC is always true because we deliver the ATX file of the virtual antenna, thus you can apply the phase center corrections in any further process. The approx_pos value is the longitude/latitude values that have been input when posting the VRS. The leap_seconds value is the delta time in seconds between GPS time and UTC time at the epoch of observation. The conversion between these two time scales can be done with the following formula : UTC = GPS - leap_seconds.

{
    "antenna": "RINEXLAB_V1_ANT NONE",
    "antenna_height": 0.0,
    "apc": true,
    "approx_pos": [
        0.185106299,
        47.747613721
    ],
    "ended_at": "2021-02-08 04:00:00 GPS",
    "leap_seconds": 18,
    "name": "TESA",
    "rate":1,
    "receiver": "TRIMBLE NETR5",
    "started_at": "2021-02-08 02:00:00 GPS"
}

The surveys list

You can access the list of your surveys in the menu VRS > My surveys. The list is organised by survey. The name and the date of creation of the survey are displayed in the header. Click on it to scroll down the list of associated VRS. Download the RINEX of the VRS with the download button. You can make a bulk download of the survey by selecting all VRS. You can search for surveys by name in the dedicated field.

The surveys maps

You can access the map of your surveys in the menu VRS > Surveys map. The markers represent the virtual stations. By clicking on a marker, you can see its metadata. You can search for surveys by name. Only the results found are then displayed on the map.

What is VRS

VRS stands for Virtual Reference Station. It is a GNSS station whose satellite observations were not obtained by measurement but by calculation. This makes it possible to simulate the presence of a permanent station in the immediate vicinity of your working area, and thus to shorten the baselines to the GNSS rover in a differential calculation. The observations of the virtual station are derived from the observations of surrounding permanent stations. From these stations, the errors affecting the GNSS signal along its path can be modelled. This modelling is valid over the region surrounded by these stations. In this region, the GNSS errors can then be known at any location. A reverse differentiation can therefore be made from the nearest station to express the satellite observation of the virtual station.

Where can I use VRS and what datum can I use

The VRS service can be used in the following countries. The list contains the datum you should select when working in the country.

  • Europe : France mainland (RGF93), UK, Ireland, Spain, Germany, Switzerland, Italia, Czech Republic, Austria, Belgium, Luxembourg, Netherlands, Finland, Sweden (ETRF2000 for all)
  • America : USA (NAD83), Brazil (SIRGAS-CON)
  • Indian ocean : La Réunion (RGR92)

We make our best to add more countries to this list. Contact us to ensure that your working area is covered. If ever the datum you usually work with is different from our recommendation, contact your local geodetic authority to know how to convert the coordinates from the RinexLab to the right coordinate system.

Can I request a VRS if its start or end time is in the future ?

Yes you can ! This will be recorded and pending until we can generate it. The process is likely to be started around two hours after the end time.

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