GNSS基本概念（7）：Android 手机GNSS参数意义（上）

train/[drive_id]/[phone_name]/ground_truth.csv - Reference locations at expected timestamps.

• MessageType - "Fix", the prefix of sentence.

• Provider - "GT", short for ground truth.

• [Latitude/Longitude]Degrees - The WGS84
  latitude, longitude (in decimal degrees) estimated by the reference
  GNSS receiver (NovAtel SPAN). When extracting from the NMEA file, linear interpolation has been applied to align the location to the expected non-integer timestamps.

• AltitudeMeters - The height above the WGS84 ellipsoid (in meters) estimated by the reference GNSS receiver.

• SpeedMps* - The speed over ground in meters per second.

• AccuracyMeters - The estimated horizontal accuracy radius in meters of this location at the 68th percentile confidence level. This means that there is a 68% chance that the true location of the device is within a distance of this uncertainty of the reported location.

• BearingDegrees - Bearing is measured in degrees clockwise from north. It ranges from 0 to 359.999 degrees.

• UnixTimeMillis - An integer number of milliseconds since the GPS epoch (1970/1/1 midnight UTC). Converted from GnssClock.

[train/test]/[drive_id]/[phone_name]/device_gnss.csv - Each row contains raw GNSS measurements, derived values, and a baseline estimated location.. This baseline was computed using correctedPrM and the satellite positions, using a standard Weighted Least Squares (WLS) solver, with the phone's position (x, y, z), clock bias (t), and isrbM for each unique signal type as states for each epoch. Some of the raw measurement fields are not included in this file because they are deprecated or are not populated in the original gnss_log.txt.

• MessageType - "Raw", the prefix of sentence.

• utcTimeMillis - Milliseconds since UTC epoch (1970/1/1), converted from GnssClock.

• TimeNanos - The GNSS receiver internal hardware clock value in nanoseconds.

• LeapSecond - The leap second associated with the clock's time.

• FullBiasNanos - The difference between hardware clock (getTimeNanos()) inside GPS receiver and the true GPS time since 0000Z, January 6, 1980, in nanoseconds.

• BiasNanos - The clock's sub-nanosecond bias.

• BiasUncertaintyNanos - The clock's bias uncertainty (1-sigma) in nanoseconds.

• DriftNanosPerSecond - The clock's drift in nanoseconds per second.

• DriftUncertaintyNanosPerSecond - The clock's drift uncertainty (1-sigma) in nanoseconds per second.

• HardwareClockDiscontinuityCount - Count of hardware clock discontinuities.

• Svid - The satellite ID.

• TimeOffsetNanos - The time offset at which the measurement was taken in nanoseconds.

• State - Integer signifying sync state of the satellite. Each bit in the integer attributes to a particular state information of the measurement. See the metadata/raw_state_bit_map.json file for the mapping between bits and states.

• ReceivedSvTimeNanos - The received GNSS satellite time, at the measurement time, in nanoseconds.

• ReceivedSvTimeUncertaintyNanos - The error estimate (1-sigma) for the received GNSS time, in nanoseconds.

• Cn0DbHz - The carrier-to-noise density in dB-Hz.

• PseudorangeRateMetersPerSecond - The pseudorange rate at the timestamp in m/s.

• PseudorangeRateUncertaintyMetersPerSecond - The pseudorange's rate uncertainty (1-sigma) in m/s.

• AccumulatedDeltaRangeState - This indicates the state of the 'Accumulated Delta Range' measurement. Each bit in the integer attributes to state of the measurement. See the metadata/accumulated_delta_range_state_bit_map.json file for the mapping between bits and states.

• AccumulatedDeltaRangeMeters - The accumulated delta range since the last channel reset, in meters.

• AccumulatedDeltaRangeUncertaintyMeters - The accumulated delta range's uncertainty (1-sigma) in meters.

• CarrierFrequencyHz - The carrier frequency of the tracked signal.

• MultipathIndicator - A value indicating the 'multipath' state of the event.

• ConstellationType - GNSS constellation type. The mapping to human readable values is provided in the metadata/constellation_type_mapping.csv file.

• CodeType - The GNSS measurement's code type. Only available in recent logs.

• ChipsetElapsedRealtimeNanos - The elapsed real-time of this clock since system boot, in nanoseconds. Only available in recent logs.

• ArrivalTimeNanosSinceGpsEpoch - An integer number of nanoseconds since the GPS epoch (1980/1/6 midnight UTC). Its value equals round((Raw::TimeNanos - Raw::FullBiasNanos), for each unique epoch described in the Raw sentences.

• RawPseudorangeMeters - Raw pseudorange in meters. It is the product between the speed of light and the time difference from the signal transmission time (receivedSvTimeInGpsNanos) to the signal arrival ti