Predicted GNSS data

Predicted GNSS data contains predicted navigation models (orbit and clock parameters) for
satellites, covering several days into the future. Unlike real-time A-GNSS data, which reflects
the current state, predicted data allows devices to operate without a network connection
by using pre-downloaded navigation models.

Using stored predicted navigation models allows the device to shorten the TTFF even when
it does not have a data connection at the time of positioning. The device can download
prediction data in advance and use the appropriate navigation models when needed.

The HERE GNSS Data API provides predicted navigation models for the following satellite systems:

Note

QZSS is not supported for predicted navigation models.

Note

The values in the table above are based on the current service configuration and may change
in the future. The validity period of each LPP message is provided in the response,
so clients should rely on the response headers instead of the values in the table above.

When to use predicted data

Predicted GNSS data is recommended in the following scenarios:

• Offline positioning: The device may not have a network connection when positioning is needed.
  By downloading predictions in advance, the device can achieve fast TTFF without connectivity.
• Reduced network dependency: Minimizes the frequency of network requests by providing
  navigation models that remain valid for days.
• Low-power applications: Battery-operated devices that wake up periodically can rely on predicted assistance data instead of establishing a network connection for each fix, enabling faster position updates and reduced power consumption.

How predictions work

The prediction data is delivered as a series of LPP messages, each covering a specific
time interval (called the validity period). The device selects the LPP message whose validity
period covers the current time and uses its navigation models for positioning.

The service returns up to 48 hours of prediction data per request. To download predictions
for the full prediction period, the client sends follow-up requests using the value from
the X-Prediction-Next response header. See
Prediction data request for details.

Supported data elements

Compared to the data elements described in GNSS assistance data,
prediction LPP messages contain only the GNSS-NavigationModel data.
Predicted navigation models are only provided for operational satellites of each constellation.
Predictions are not calculated for known outage periods when a satellite is not available.

Related information

• Prediction data request
• GNSS assistance data
• LPP ASN.1 schema