Configuring a Scenario
A scenario is the dataset describing a simulation in terms of starting position, duration, trajectory, events and other parameters which you may want to include in your simulation. GSG units come with several predefined scenarios (depending on the GSG model). You may also use StudioView to create your own scenarios, save them to a file and upload them to the GSG unit. The GSG unit will execute the simulation in accordance with the parameters specified in the scenario file.
Scenario data is stored in a text file. To show/hide text of scenario file, click .To configure the scenario, fill in the appropriate fields under the tabs described below.
Once you have completed your scenario configuration, save it and upload the scenario file to the GSG unit by clicking .
Note: StudioView stores all files in a directory chosen during the installation process. By default, the repository is located at C:\Users\UserName\Documents\Spectracom\GSG StudioView\Repository. You may save your scenario in any other folder, but please note you must also save any trajectory, event, antenna pattern, or navigation files you may want to include to your scenario in the same folder.
The Scenario Editor provides access to all essential scenario parameters. To access the Scenario Editor, click , or navigate to Tools > Scenario Editor:
- The Start time is specified using GPS Time. The GPS Time is always used when displaying time. This is not equal to the UTC time frequently displayed by the receivers. Contrary to the GPS time, UTC contains leap seconds.
The Start Time can be a set time, or the current time derived from an NTP server specified in the Network Configuration settings of GSG device. To use this feature, check Synchronize from the NTP server checkbox.
- If the current time from the NTP server is used, next the startup will be delayed up to 2 minutes to allow the simulation to load required data. The start time is aligned to the next full GPS minute. The NTP (UTC) timescale is converted to the GPS timescale by a UTC-GPS offset defined in the NTP server settings.
- Using NTP as start time in conjunction with Ephemeris set to Download is subject to licensing options, as it requires the Simulate Now option to be present. In this configuration, the GSG will simulate the sky as it is in that start position at current time. This functionality is currently only available for the GPS constellation. Please also note that the availability of good ephemeris data cannot be guaranteed, but periods where no data is found and hence no signals can be generated, may occur.
- The Duration of the scenario replay can be set to a number of days, hours and minutes. The scenario can be set to:
- Looping, means that scenario will restart again right after execution is finished
- Forever, GSG will download needed navigation data from Internet and run scenario until user will stop it
- One-go, in which case it executes only ones and then returns to main menu of GSG device. Note that the option “forever” only works when the Ephemeris option is set to ‘Download’ (Start) Position.
- The Start position is specified using WGS84. Note that this also concerns the altitude (ellipsoid height) and that this is not the same as the MSL often output by receivers. StudioView provides automatic conversion between different coordinate input formats; decimal degree, degrees-minutes, degrees-minutes-seconds and ECEF format.
Under the Signals tab, you can determine which satellite signals you want to use, the type of environment, and possible Interference signals:
Under this tab, you can explicitly set the maximum number of satellites to be simulated, with separate settings for GPS, GLONASS, Galileo and Beidou. When the Auto keyword is used, the GSG unit will automatically select the highest satellites available and generate the maximum number of satellites that your GSG model allows. You can also configure the number of SBAS satellites to be simulated.
It is possible to configure the frequency bands and possible (pseudo-P(Y)) encryption by clicking on the checkbox for the corresponding constellation and band. The availability of all elements for simulation (e.g., GPS L2C, L5 and Galileo) is dependent on the installed licensing options and your GSG model .
- For each constellation, you may specify the maximum number of signals in view for a given time, clicking the up or down arrows. Or, just type the number. For maximum number, also see the field tooltips.
Note: The maximum number of signals depends on your GSG model. The unit will decrease the number of signals specified in the scenario to fit your license options. If Auto is selected, the GSG unit will use maximum number of channels.
- Use checkboxes to include or exclude a particular frequency band (e.g. L1, L2, E1, L2 P, etc.) from your simulation scenario. If a checkbox is grayed, it means that it is not supported or the only displayed choice is available.
- There can be 0, 1, 2, or 3 SBAS satellites per scenario. The GSG unit will select SBAS SV based on their elevation with respect to the user position. When the scenario is running the SBAS satellite positions and speed will be updated with the information found in the SBAS messages.
Under Propagation environment you can select an environment model which will impact signal propagation. There are four models available:
- Open (full clear view of the sky, i.e. no obstructions).
The simulation is carried out based on probability, applying different building densities (sparse <> dense). The feature offers some adjustability. For more information, see Propagation Environment Models.
- By specifying the Elevation mask, you define the satellite-in-view cut-off range. All satellites which are below this range will be dropped off and replaced with better/higher satellite (if available). For more information, see Elevation mask.
You may also add Interference signals and Multipath signals to the scenario. The maximum number of Interference/Multipath signals is 8.
Interference signals are used to degrade the reception of GNSS receivers. To add an Interference signal, click . To add a signal, use default values or specify Interference signal parameters by expanding the list. You may also collapse or expand all items by clicking on the closed book or open book icon, respectively. To delete an Interference or Multipath signal, click .
Under the Navigation tab, you link files that describe the trajectory, events, environment, vehicle model and navigation data to your scenario:
Any user trajectory can be simulated using the GSG. You can choose to use one of the built-in trajectories or upload a trajectory file created in the Trajectory Editor or RSG Trajectory Editor of StudioView. To select one of built-in trajectories, click on Circle, Static, 3GPP and set up parameters if needed.
To attach a pre-installed trajectory or your own trajectory to the scenario, click File and pick a trajectory file from the dropdown menu. To add your own trajectory file to this dropdown list, you have to create a new trajectory first and then save it in the repository.
An Events file describes some specified events during scenario execution. To create events file, see Defining Events in StudioView.
Support for environmental or vehicle models in GSG simulators is via compressed keyhole markup language files (kmz) popularized by Google Earth. A simple way to create these files is with the tool SketchUp available from Trimble® Navigation, see https://www.sketchup.com/.
An Environment model is a 3D model of the environment, describing terrain, buildings, etc. All environment models used must have a ‘geo-location’ added to them before they can be used by in simulation. Environmental Modeling is used first and foremost to simulate urban canyons, or tunnels. You can create blocks, representing buildings/obstructions, and place them on the map along the trajectory. The power level of the satellites will be blocked or reduced in the vicinity of the buildings due to the obstruction of the line of sight near these virtual buildings.
A vehicle model represents a 3D model of the vehicle. The vehicle model will move with the simulated trajectory. The vehicle model will also follow any pitch/roll/yaw movements simulated, i.e. if the vehicle rolls by 90 degrees, half of the sky is likely to be blocked by the vehicle itself, depending on vehicle model used. The body center of the simulated vehicle will be in the origin position of the model. The antenna position can differ from the body center position by configuring lever arm values in the scenario configuration. The antenna position can also be specified in the vehicle model file by adding a component named “RecAnt”. If both lever arm and RecAnt are set, the receiver antenna position as set in the vehicle model takes the precedence. The vehicle model does not need a geo-location.
Vehicle models can also be created with the software tool “Sketchup”, see above.
If a satellite is blocked by an object from either the environment or vehicle model, i.e. it is not visible by the receiver antenna, its power level is set to OFF.
GSG can successfully handle vehicle models with up to 130 triangles and models should be optimized for low polygon count. The triangle count is limited to a total of 300 for the combined environment and vehicle models.
- Navigation data allows you to specify Almanac and Ephemeris files to be used during simulation. Next to the Default option, you can download navigation data from the official web sites, or use your own Almanac or RINEX files. For more information on RINEX files, see Editing RINEX Files in StudioView.
To download navigation data from the official web sites, click , and then click . The navigation data for the scenario start time and number of satellites you specified under the Signals tab will be downloaded. To add the navigation data files to your scenario, click and select the files needed.
To edit navigation data in the RINEX editor, select the file from the list and click .
Under the Atmospheric models tab, you can model the Ionosphere and Troposphere.
The GSG unit comes with built-in support for an Ionospheric model. When set to On, by default the used model is a reverse model of the model described in IS-GPS-200D, section 126.96.36.199.2.5. When set to Off, no delays caused by the Ionosphere are used in the simulation. GSG also supports simulation of Ionospheric delays using files in IONEX format. To specify a particular file, select Files and choose it from Repository.
Under the Antenna tab, you determine which type of antenna you would like to simulate, as well as the lever arm, which specifies the antenna position relative to the vehicle center of movement.
Under the RTK tab, it is possible to simulate a virtual Base Station: Specify its geographic coordinates and altitude, as well as an RTCM protocol version and type of RTCM messages to be simulated.
Under the Satellites preview tab, you can visualize the satellites in view.