Scenarios utilizing signal obscuration simulate the blocking of GNSS signals by objects placed along the trajectory route. Typical use cases are the simulation of urban "canyons", tunnels, etc.
Environmental models in GSG simulators are supported through compressed keyhole markup language files (kmz), popularized by Google Earth™. A simple way to create these files is by using the 3D drawing tool SketchUp™, available from Trimble Navigation Limited: www.sketchup.com.
Two kinds of models can be configured in a scenario, Vehicle model and Environment model:
An environment model is a 3D model of the environment, e.g., buildings, ground, etc. All environment models used must have a geo-location added to them before they can be used for simulation purposes.
A vehicle model represents a 3D model of the vehicle. The vehicle model will move with the simulated trajectory. The body center of a simulated vehicle will be in the origin position of the model, and all trajectory movements defined in the simulation will act on the body center. The vehicle model should be placed so that its nose points to the north.
The vehicle model will also follow any pitch/roll/yaw movements simulated, i.e. if the vehicle model rolls by 90 degrees, half of the sky is likely to be blocked by the vehicle itself (depending on vehicle model used).
The antenna position oftentimes is not in the same location as the vehicle body center position. In the simulation, this can be adjusted by configuring the lever arm values (see Lever arm).
The antenna position can also be specified in the vehicle model file by adding a component named RecAnt. In the event that both lever arm, and RecAnt are set, the receiver antenna position as set in the Vehicle model takes precedence. The vehicle model does not need a geo-location.
If a satellite is blocked by an object from either environment or vehicle model, i.e. it is not visible by the receiver antenna, its power will be set to OFF.
GSG can successfully handle vehicle models with up to 130 triangles. Models should be optimized for a low polygon count. The triangle count is limited to a total of 300 for the combined environment and vehicle models.
For additional information, see the Spectracom Technical Note Vehicle Modeling.