Guide GNSS satellite map

Guide: the GNSS satellite map

What it is. In the GNSS mode, the Map view draws where the navigation satellites are right now: GPS, GLONASS, Galileo, BeiDou and QZSS. Each one is a marker at its sub-satellite point (the spot on Earth directly below it), labelled with its RINEX name (G12, E05, C21, R07, J02) and coloured by constellation.

What you need

A GNSS-capable radio and an active GNSS antenna (most are active, so the bias-tee needs to be on; see the bias-tee tooltip about DC shorts). The GNSS mode page has the details.

Step by step

1. Choose GNSS in the mode list and start the receiver.
2. At the top of the mode panel switch the view: Sky, Map, Channels, Interference, Clock. Choose Map.
3. Wait. Satellites appear when the receiver has decoded a complete, parity or CRC checked navigation message for them. This takes from tens of seconds to some minutes.
4. Hover a marker. The tooltip says whether the satellite is tracked, whether it is used in the fix, and whether its position comes from the ephemeris or only from the almanac (marked "(almanac)"), and the ephemeris age.
5. Markers are dimmed when the satellite is not currently tracked.

How the positions are computed

Positions come from the navigation message the receiver decodes, evaluated at the current signal time with the algorithms from the satellite system documents (the Kepler solution of IS-GPS-200 for GPS-like systems; the GLONASS state vector integrated). Height and the WGS-84 latitude and longitude of the sub-satellite point are shown. SBAS satellites have no orbit here. Coverage is GPS, QZSS, Galileo (E1B I/NAV), BeiDou (D1 and D2) and GLONASS, whatever the receiver has decoded an ephemeris for.

Sharing on the public map

On map.on-air.dev satellites appear under the kind gnss, but only with the map-sharing opt-in on (see Map sharing):

• Sent only from a broadcast ephemeris that is still valid (4 hours from the reference time for GPS, QZSS, Galileo and BeiDou; 30 minutes for GLONASS).
• An almanac position is shown in the app only and never uploaded.
• No trails. Elevation and azimuth are deliberately not uploaded: together with the sub-satellite point they would reveal where your receiver is.

Limits

This was checked with the simulator's ephemerides and closed-form orbits; no real-signal hardware check is claimed (check the mode page for the current status). Time scales (GPST, GST, BDT and the GLONASS day) come from the receiver's existing conversions.

Troubleshooting

• Empty map: no ephemeris yet; check antenna, bias-tee and sky view in the Sky view and Channels view.
• Markers in the wrong place: wait until the ephemeris age is small; an almanac position is approximate.
• Interference: the Interference view flags suspicious conditions (for example an ephemeris that disagrees with the almanac); be careful with a position while it flags.

Related

GNSS | Clock sources | Map sharing | Live map