Base Stations Management

Introduction

The base stations management dialog box is a very important part of GNSS/INS post processing. It is used to configure and choose the GNSS augmentation processing mode. It could be Precise Point Positioning, single base station PPK or complex VBS networks.

In this dialog box you can download GNSS base stations from CORS networks, import your own base station data, select which base stations to use in the solution an even compute a static PPP solution to control the base station position.

Base Stations Management Dialog

The base station management panel is shown during the project creation wizard so you can review and define how to access centimeter level accuracy. You can also open it at any time to review or change the selected processing mode by clicking the  button in the main Qinertia tool bar.

General Layout

The base station management dialog box is composed of six main sections:

Base Station Icons

Qinertia represents each base station graphically on a map using icons and the base station marker name. Each base station is represented by specific icons to easily identify the base station type:

The icons are also used to represent the base station status using color codes as well as which base stations are selected in the processing:

Project Creation

Qinertia automatically display all surrounding base stations from CORS networks within a 200km radius. All theses base stations are indicated as pending and Qinertia will try to download automatically the five closest base stations.

Import a Base Station

You can import as many base stations you would like by simply drag-and-dropping base stations files to the base station management map as shown in the screenshot below.

Qinertia accepts RAW GNSS data in RINEX and can read directly binary proprietary protocols from Septentrio, Ublox, Novatel and Trimble GNSS manufacturers.

When the base station is imported, Qinertia will try to parse information such as the marker position, the antenna and so on. If there is a missing information, you will be warned and asked to fix it.

If Qinertia is not able to extract the base station position or if the position is marked as not accurate in the import files, Qinertia will also indicate it

Base Station Details Dialog

This dialog box displays all information and status for a specific base station and also let you change some parameters such as the base station antenna or positions. You can also perform a static PPP computation to validate or find the precise base station position.

To open this dialog box, simple double click on any base station or click on the More button for a selected base station. This dialog box will also be displayed if you have errors on a base station and try to use it for the processing so you can review invalid parameters.

Base Information

This panel displays all the information on the base station such as its position, the receiver name, the CORS network provider and so on.

You can manually enter the base station position in any datum and select which position to use for the GNSS/INS computation:

• Published - Position published by the CORS provider or read from a RINEX file
• Manual  - Select the position entered manually in this dialog box
• PPP - Select the static PPP solution if one has been computed

Latitude/Longitude

You can display and enter latitude and longitude in decimal degrees or using the above Degrees, Minutes, Seconds method. Simply switch between the two modes by clicking on the Latitude or Longitude labels. The latitude is positive north and longitude positive east.

Compute a static PPP

You can compute a static PPP solution on any base station from this dialog box. This is very helpful if you are using your own base station and don't know its location precisely.

1. To start a static PPP computation, simply click on the Compute button from the base station detail
   
2. Qinertia automatically download the missing resources such as precise ephemeris data and compute the PPP solution
   
3. Once the computation is done, you get horizontal and vertical offset compared to the selected position type. This let you easily compare a publised or manually entered position with the PPP result.
   In the example below, we have a mistmatch between the PPP solution and the published base position.
   
4. If you decide to use the PPP solution instead of the published base position, simply select it in the drop down list as shown below.
   

PPP Solution Datum

The PPP solution is computed using precise ephemeris data so the position is expressed in the datum used to generate the ephemeris data. If you use precise ephemeris data automatically downloaded by Qinertia, you will have a position expressed in ITRF2014 datum at the observation epoch.

Base Station Antenna

In this panel, you can change the base station antenna, select the reference point and apply a vertical offset between the reference point and the base position. You should carefully validate theses parameters as they affect directly the computed solution altitude.

If you have the Latitude, Longitude and Altitude of a geodetic ground point, as represented in the photo below, you have to enter the antenna height parameter. This is the vertical offset to apply between the geodetic point to the antenna selected reference point.

Base Station Operations

This panel displays all operations that have been executed and any ongoing operation. You can monitor what is happening on a specific base station and check if an operation has failed.

Base Station Status

This is a sort of check list for a base station. All these status have to be green to consider the base station to be valid. If the general base station status is indicating an error or a warning, you should review this panel to get more details.

Base Station Coverage

You can easily control if all measurements have a good overlap. This can be very helpful if, for example, you have imported base station data from the previous day by error.

GNSS Global Resources Management

This advanced dialog box lists the imported and used global GNSS resources such as the GNSS ephemeris, satellite orbits and clocks files.

You can also import your own resources from any RAW GNSS file or from standard RINEX such as SP3 and CLK files. Simply drag&drop all the files on the right side of the panel.

The Force re-download button can be useful if Qinertia wasn't able to download some resources and you would like to retry.

You can right click on any file and select the Show in Explorer contextual menu to view the downloaded files directly.

Processing modes

Qinertia offers several GNSS augmentation algorithms to deliver centimeter level accuracy solutions. You can choose between PPP, Single base station PPK or Virtual Base Station (VBS) network processing. Qinertia can also pickup automatically the best solution based on the trajectory and available base station and GNSS data. Please read also the Processing a Log page to get an in-depth explanation of all available processing modes in Qinertia.

Loosely Coupling

GNSS base station management panel has no effect for reprocessing and loosely coupled INS solutions as these two processing modes use the real time trajectory (PVT) directly.

Auto Mode

During project creation, Qinertia will try to download all nearby base stations to check for data availability and quality. Then, the software automatically selects the best available processing mode to reach centimeter level positions.

The automatic mode uses several metrics and techniques to guess the best solution based on the following preference order:

1. Single base station PPK
2. Virtual Base Station PPK
3. Precise Point Positioning

Once this step is done, you can manually change the GNSS base stations configuration and for example import your own base station data and/or override the choices automatically done by Qinertia. At any time, you can ask Qinertia to suggest again the best GNSS augmentation solution by clicking on the Find best button as shown in the screen below:

If you have added or removed a base station and would like Qinertia to check again what is the best processing mode, you should manually trigger it by clicking the Find best button. Qinertia will never trigger this action automatically except for the first time during the project creation.

Single Base PPK

This is the most accurate positioning mode and it is available if you select one and only one GNSS base station. This processing mode uses differential corrections data from a single base station to achieve a sub centimeter Post Processed Kinematic solution. The only limitation of this mode is base station availability nearby the trajectory.

The position accuracy decreases as the distance from the GNSS base station increases (also called baseline). If a part of the trajectory is too far from the base station, Qinertia will even not be able to fix ambiguities anymore resulting in a degraded accuracy.

Qinertia displays the expected accuracy / confidence using three circles:

• The green area 20 km radius, you should get RTK fixed results with optimal results 1-2 cm
• The yellow area 40 km radius, depending on the atmospheric conditions and GNSS data quality you can have RTK Fixed and Float solutions
• The red area 60 km radius, you should get RTK float solutions and even no RTK solution at all if you have difficult atmosphere conditions. You can however still get RTK Fixed positions if the atmosphere conditions are clean.
• Further the red radius, nothing is guaranteed but you can still give it a try as you can get pretty decent results if the atmospheric conditions are clean.

Virtual Base Station (VBS)

Introduction

This mode overcomes typical single base station limitations by extending a lot the maximum baseline from 20 km to more than 100 km without noticeable loss of precision. To do this, Qinertia uses at least three bases stations to create a network to map all atmospheric disturbances. Within this network, Qinertia is able to deliver a PPK solution very similar to a single base station short base line with no convergence time and perfectly suitable for harsh GNSS conditions.

The VBS algorithm is also the way to go to support corridor mapping as Qinertia can create a network around a long trajectory. The example below, shows an helicopter acquisition that spread across more than 180 km and Qinertia has automatically created a VBS network of 12 base stations.

Create a VBS network

To create a VBS network, please follow these steps:

1. Import/download all the bases stations you would like to use in the VBS network. You can mix CORS base stations with your own base stations.
2. Select which base stations should be used in the VBS network by drag&dropping the bases from the map to the base station list on the left.
3. Qinertia will display a preview of the VBS solution with very preliminary quality indications based on the network geometric topology
   
4. Before you can continue, you should run the VBS network validator by clicking the Validate network button. Qinertia will automatically download missing data and compute a static PPP solution on the master base station to check for any position offset.
   
5. Once the validation is completed, Qinertia computes a more accurate expected quality indication and status. In our example, Qinertia has detected a mismatch between the master base station pmbg position and the one computed using the static PPP solution.
   
6. You can open the VBS report by clicking the button to get more detailed information about the VBS preview but keep in mind it is still a preview and the real VBS computation is done when you process the log.

Precise Point Positioning (PPP)

This GNSS positioning mode is available worldwide and doesn't need any base station data. It is using global precise Ephemeris, Clock and Bias data that are available 24 hours after the mission to compute an absolute centimeter-level accuracy position.

The computed solution is expressed in ITRF2014 datum if you are using Ephemeris data automatically downloaded by Qinertia. You can also supply your own Ephemeris data using the Global Resources Management dialog box.

Qinertia runs a forward/backward PPP computation to eliminate convergence time but the PPP solution is less accurate and robust than Single Base Station and VBS modes.