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

Quick overview

To use the PPP service, click PPP in the main menu after you logged in. This will open the calculation form.
Name your survey, select the datum in which you want to express the coordinates. Then add up to 4 raw observation files to be processed in the same survey. For each file, indicate the rover name, antenna height, data format, and mode.

Datum

Select here the datum in which the coordinates of the rovers of this survey will be expressed. The possible choices are ITRF2014 and ETRF2000 for now. WGS84 is not offered because this datum is not compatible with precision positioning applications. If you are absolutely looking for a rover in this datum, choose ITRF2014, but it is likely that the definition of your project is incorrect. You can contact us for more information.

Antenna height

If you do not specify an antenna height, it will be set to 0.0m by default. The antenna height is the elevation offset between the GNSS antenna reference point and the point for which you wish to obtain the coordinates. The antenna reference point is the bottom of notch if it is registered in the NGS database - see the file here. If not, it is the antenna phase center.

Data format

If you do not know the data format, leave on Auto. The supported formats are as follows: RINEX v2, RINEX v3, UBX, Trimble T01, T02, Leica M00, Septentrio SBF. If your receiver cannot produce raw data in any of these formats, please contact us.

Mode

The determination mode can be kinematic or static. In kinematic mode, a position is expressed for each satellite measurement epoch. This mode is suitable for calculating the trajectory of moving receivers. In static mode, a single solution is provided at the output of the calculation. This mode is suitable for stationary receivers, for example to express the position of a geodetic point precisely.

Add a rover to the survey

To add a rover, click on the plus sign to the right of the grid.

Start the process

You must be the owner of a valid token with a positive number of credits to start the processing. Once the survey has been created and the data files associated, you cannot modify it or add rovers. The processing will start automatically. You can find all your surveys and their processing status in the menu PPP > My surveys. You can also see them on a map in the PPP > Surveys map menu.

The results file

When processing is complete, the result file is available for download from the PPP > My surveys page. There is one zip file per rover. In this archive there is a position / trajectory file in CSV format, and a metadata JSON file. The CSV file contains the position (if static mode) or the trajectory (if kinematic mode) in latitude / longitude / height in the requested datum.

Exemple of a CSV results file for a kinematic process

datetime,lat,lg,h,solution,all,fixed,pdop,sn,se,sh,co_en,co_eh,co_hn
2020-11-25 01:00:00.00,47.946518307,0.180895374,96.7518,L0T_Float,26,0,1.6,0.005,0.0041,0.0112,0.0229,0.426,-0.2879
2020-11-25 01:00:01.00,47.946518308,0.180895353,96.7695,L0T_Float,26,0,1.6,0.0038,0.0032,0.0087,0.0189,0.4303,-0.2892

The columns are :

  • datetime : date and time of the position [Y-m-d H:M:S.ss]
  • lat : latitude of the rover [decimal degrees]
  • lg : longitude of the rover [decimal degrees]
  • h : ellipsoidal height of the rover [meters]
  • solution : positioning solution, Fixed of Float, basically
  • all : number of satellites in view
  • fixed : number of satellites with fixed ambiguity
  • pdop : PDOP value
  • sn : estimation of the position accuracy in the North-South direction [meters]
  • se : estimation of the position accuracy in the West-East direction [meters]
  • sh : estimation of the position accuracy in the vertical direction [meters]
  • co_en : Eastings/northings correlation coefficient of the coordinates [meters]
  • co_eh : Eastings/height correlation coefficient of the coordinates [meters]
  • co_hn : Height/northings correlation coefficient of the coordinates [meters]

Exemple of a CSV results file for a static process

datetime,lat,lg,h,nsat,se,sn,sh,co_en,co_nh,co_he
2020-11-25 01:00:00,47.94651833282349,0.1808954620476796,96.7567,13.8,0.0003,0.0002,0.0006,0.004,-0.175,0.010

 The columns are slightly different in static mode :

  • nsat : the average number of satellites in view during the process

The metadata file

The metadata file gathers the name of the rover, start and end time of the observations session, antenna and receiver types, antenna height, and a very important information called "apc". This value tells you if the antenna phase center corrections has been applied during the process. If No, the results are expressed at the antenna phase center, minus the antenna height. If Yes, the results are expressed a the antenna reference point - or APC, minus the antenna height. The APC is often the bottom of mount. If you have any doubt, ask your supplier about this. But be aware that any confusion on this field could lead to a height error between 0 and 20 cm in the results file. The approx_pos value must not be considered as a precise position. It can be used to display the point on a map, but absolutely not to do precise surveying. 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": "LEIAS10         NONE",
    "antenna_height": 0.0,
    "apc": true,
    "approx_pos": [
        0.180895522,
        47.946518318
    ],
    "ended_at": "2020-11-25 23:59:30",
    "leap_seconds":18,
    "name": "ARNA",
    "rate":30,
    "receiver": "TRIMBLE NETR5",
    "started_at": "2020-11-25 01:00:00"
}

The surveys list

You can access the list of your surveys in the menu PPP > 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 rovers. Download the results of the calculation with the download button. You can make a bulk download of the survey by selecting all rovers.
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 PPP > Surveys map. The markers represent the rovers. In kinematic mode, they represent the position at the first satellite observation time.
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 PPP

PPP stands for Precise Point Positioning. It is a method of calculating the coordinates of a GNSS receiver that allows centimetric precision in static or even kinematic measurements under excellent measuring conditions.

The principle of this positioning mode is to model the errors affecting the path of the signal from the satellite to the receiver: satellite orbit and clock offsets, ionospheric and tropospheric delay. The ionospheric part is the most complex to model, which is why an iono-free combination of the multi-frequency signals emitted by the satellites is normally used. This means that you absolutely need a multi-frequency receiver when you do PPP.

PPP outputs positions expressed in the satellite coordinate system. Currently this is ITRF2014. It is rare for surveyors to work locally with this system because it is mobile in time. In concrete terms, when you give the ITRF2014 coordinates of a point, you are also supposed to give the time of validity and the associated travel speed, which is not always possible - by the way this is exactly the same when you use WGS84. It is preferable to work in a system consistent with your area of intervention, such as ETRF2000. It is important to understand this because the differences in coordinates between these systems can be as much as 1 metre. To convert ITRF2014 coordinates in continental systems, there are formulas built into our algorithm. Thus, when you select the ETRF2000 datum when creating a PPP survey, the last step of the processing is to convert the ITRF2014 results to ETRF2000. If you are looking to obtain positions in WGS84, be aware that this datum is not at all suitable for precision positioning, and you will certainly need to find out a little more about the right datum to use.

Where can I use PPP

PPP can be used anywhere on Earth as long as your receiver picks up at least 4 satellites. Of course, the more satellites you see, and the better the signal quality, the better your results will be.

What accuracy can I expect

In static mode, you can obtain a precision of a few centimetres in 1 hour of observations. The longer the session, the better the expected accuracy. With a few hours of observations, you can expect 1-2 cm accuracy.
In kinematic mode this is more variable. In excellent observation conditions, with a stationary time at the beginning of the session, with few signal interruptions, you can also achieve centimetric precision. In reality, as it is difficult to always evolve in these ideal conditions, it is more common to have 10 - 20 cm accuracy.

What datum can I use

You can use any coordinate system as long as there are pass formulas between it and the ITRF2014. We have integrated some of the common datum directly into our algorithm - currently ETRF2000 only, more are coming, but if yours is not in the list, you can do the conversion yourself from the results file provided. In this case, please contact us too. We will try to integrate it into our service. Remember that if you are using the ITRF2014 datum, the coordinates are valid at the time of measurement. Depending on the speed of tectonic movement, the coordinates may change by several centimetres in a year. This is why we always state in our reports that the coordinates are obtained in ITRF2014 @ [measurement epoch].

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