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Manual

Processing engine

Under the hood, Virtual-lab runs the open-source package rtklib as the positioning engine This service works on a best-effort basis, and attempts to run these processing strategies in the following prioritized order:

  • Post Processed Kinematic (PPK), Virtual-lab computes a coarse estimate of the rover position using SPP in order to have a rough estimate of the receiver position and be able to automatically select the closest base station from the set of stations continuously monitored by Virtual-lab. If a nearby station is found (less than a certain baseline), then the corresponding RINEX data is downloaded in order to perform differential positioning. Alike, if you provide Virtual-lab with a base station measurements file, it will undergo PPK technique processing.
  • Precise Point Positioning (PPP), if no nearby base station is found, Virtual-lab will attempt PPP if the precise orbits and clocks for the day to be processed are found and the input data is multi-frequency.
  • Single Point Positioning (SPP), if PPP failed, the data processed using the broadcast orbits and clocks will be delivered.

Supported formats

Virtual-lab supports the following input formats to input GNSS observables (pseudorange, carrier-phases, ...):

  • Rinex 2/3
  • ublox formats (both single and multiple frequency formats). Data from chipsets such as NEO-M8T or ZED-F9P are supported. This obviously cover also all GNSS receivers that use these chipsets (e.g. Drotek, EMLID receivers, ArduSimple, ...)
  • Google's Android GNSS logger (smartphone data)
  • GPS Test app (smartphone data)
  • GalileoPVT app (smartphone data)
  • RTCM 3 data
  • Septentrio binary (SBF) files

Result files

This section include the information of the various file formats delivered by Virtual-lab.

GNSS processor files

When a process has been successful, a compressed (ZIP) file is generated with all the results of the process. The format of the different files included in the bundle by the GNSS processor are described in the following sub-sections.

Position files (csv)

Positions will be delivered as a comma separated file where the first line is a comment (starts with #) with a description of the fields, which are:

  • columns 1-2: Epoch of the solution, expressed as GPS week and seconds within the GPS week.
  • columns 3-5: Position longitude and latitude expressed in decimal degrees and height in meters above the ellipsoid.
  • columns 6-8: Standard deviation in meters of the North, East and Up components. Note that these values are the formal errors delivered by the position filter (i.e. square root of the postfit variances) and they do not necessarily reflect the actual error in the navigation solution. The surveyor will need an external reference to compute the actual error. However, these values can be treated as a preliminary quality metrics of the solution.

Virtual-lab will always deliver the position file corresponding to the SPP strategy (files ending with _spp.csv). If a more accurate strategy (PPP or PPK) could be performed, additional CSV will be also delivered, ending with either _ppp.csv or _ppk.csv, to indicate the strategy of the solution.

Example:

# GPSW,GPSSoW,latitude(deg),longitude(deg),height(m),sdn(m),sde(m),sdu(m)
2069,124585.300000,41.3495230130,1.6680445200,246.06570,2.3403,1.5631,4.6059
2069,124585.400000,41.3495233800,1.6680436110,246.40920,2.3403,1.5631,4.6059
2069,124585.500000,41.3495239180,1.6680507170,246.51000,2.3403,1.5631,4.6058
2069,124585.600000,41.3495241180,1.6680519850,246.22500,2.3403,1.5631,4.6058
2069,124585.700000,41.3495263560,1.6680520780,246.36660,2.3403,1.5631,4.6058
2069,124585.800000,41.3495281560,1.6680502930,245.82960,2.3404,1.5631,4.6058
2069,124585.900000,41.3495297610,1.6680474000,245.42580,2.3404,1.5631,4.6058

Position files (kml)

For convenience, the positions are converted to KML format and included in the ZIP package as well. These files can be easily opened using tools such as Google Earth, just double-click on the files and the application will open the file.

Similarly to the case of the CSV files, the KML corresponding to the SPP strategy will be always delivered. If PPP or PPK has been successful, the KML files for this strategy will be also delivered. The strategy will be part of the file name.

In addition, for quick visualization, a decimated version of the KML file is also provided. This is useful for a quick preview of files that have been taken in long data campaigns.

In case of static receivers, only the last point of the processing will be included in the KML file.

Plots (png)

As a visual summary of the processing task, a series of plots (in PNG format) are also included in the bundle. These files are:

  • height.png: Time series of the height above the ellipsoid in meters.
  • skyplot.png: Skyplot showing the distribution of the satellites that have been used for the processing. The points in the plot have different color coding, depending on the constellation. Also, the satellite ID is also shown at the last point, which is a helper to know the direction to which the satellite moved.
  • num_satellites.png: The time series of the number of satellite during the processing. The same color coding used in the skyplot has been used here. The chart is a stack plot and shows the number of satellites, at each epoch, of each constellation.
  • CNo.png: After correlation carrier to receiver noise ratio is expressed in decibel-Hertz (dB-Hz), it is a measure of the quality of the reception of the signal of each satellite, the CNo can be used as means to determine if there are interferences in the GNSS signal (if all satellites suffer the very same signal valley at the same time). Ideally highest elevation satellites should report a C/No of 51 dB-Hz
  • CycleSlips.png: Depicts the number of times the tracking of a particular satellite / signal has been lost and recovered, indcating also when those events happened in time. For carrier phase based calculations like PPK or PPP it is very important to have an as continuous as possible signal tracking as every time a singal carrier phase is lost it's relative cycle counter must be reinicialized from scratch causing the particular satellite / signal to be temporally unusable to benefit PPK or PPP solutions. Ideally there should be no vertical bars in the plot (continous tracking).
  • Multipath.png: Ionosphere detrended code minus carrier plot is a depiction of how much multipath (bounced signal on objects like trees, buildings, etc) there is present in the signals correlated by the GNSS receiver. Ideally this plot should be as close to zero as possible.

Time/Camera events (csv)

In the event that the input contained time events (usually generated from camera trigger), the output package will also contain a camera event file camera_events.csv. The file contains as many rows as time triggers (camera events) detected in the input file. Each row of the file contains the time tag, position and formal error of the camera event, with the same format as described above for the Position CSV files.

User section

In order to go to your user area, point to the top-right part of the page, where your e-mail address is displayed, and click on the arrow. A drop-down menu will be displayed. Then click "My Account" as shown in the screenshot below.

Go to my account

In your account you will find 2 areas:

  • Profile where you will be able to set your Name and e-mail address.
  • Change password, to reset your password.