$USRTH Receiver-Transmitter Relative Angles Message

Note: From time to time, Cerulean adds features to the ROVL as requested by users, some of which require changes to this message. Cerulean undertakes to maintain backward compatibly on this message, so once a field is defined and published, we try not to not move it or change its behavior. We may add new fields to the end of the message, so we recommend you allow for extra fields that you can ignore if writing a parser for this message, rather than requiring a specific field count.

Example $USRTH message:

$USRTH,358.5,1.5,2.8,142.8,52.8,37.2,2.8,

-0.6,1.9,178.1,271.9,16,T,T,1,3313,B,-2,-2*4B

Format: $USRTH,ab,ac,ae,sr,tb,cb,te,er,ep,ey,ch,db,ah,ag,ls,im,oc,idx,idq*hh

ab: apparent bearing (azimuth) to transmitter in Math degrees [Note 1, 4]

ac: apparent bearing to transmitter in Compass degrees [Note 1, 4]

ae: apparent elevation to transmitter in degrees [Note 1]

sr: slant range to transmitter in meters [Note 1]

tb: true bearing (azimuth) to transmitter in Math degrees [Note 2, 4]

cb: true bearing to transmitter in Compass degrees [Notes 1, 4]

te: true elevation to transmitter in degrees [Note 2]

er: Euler roll angle of sensor frame, in degrees [Note 3]

ep: Euler pitch angle of sensor frame, in degrees [Note 3]

ey: Euler yaw (heading) angle of sensor frame, in degrees [Note 3, 4]

ch: compass heading [Notes 3, 4]

db: Analog AGC gain, in decibels (range 16 – 82)

ah: CPU hardware supports autosync (also needs GNSS hardware) [Note 5]

ag: GNSS hardware support autosync is present [Note 5]

ls: Seconds since last autosync or distance sync command [Note 5]

im: IMU status string (four digits 0..3) [Note 5]

oc: Operating channel: “B” if Mk II hardware AND autosync installed AND set to channel B; else “A” [Note 6]

idx: Transmitter/Transponder ID decoded [Note 7, 8]

idq: Transmitter/Transponder ID queried [Note 7, 9]

hh: NMEA-style hex checksum, always the last field and following the asterisk

Note 1: this field will be empty if receiver is not locked on transmitter

Note 2: this field will be empty if receiver is not locked on transmitter or IMU data is not valid

Note 3: this field will be empty if IMU data is not valid

Note 4: See section on “Compass” vs. “Math” angles

Note 5: These fields appended March 2021; not present in earlier firmware releases

Note 6: [IDs are a deprecated feature as of 1/1/25] Field appended August 2021; not present in earlier firmware releases

Note 7: [IDs are a deprecated feature as of 1/1/25] Field appended December 2022; not present in earlier firmware releases

Note 8: [IDs are a deprecated feature as of 1/1/25] if -2, no ID was detected to be appended to the transmitter/transponder's ping. If -1, an ID was detected to be appended to the transmitter/transponder's ping but it was an invalid pattern. Otherwise, if 0..15 an ID was decoded. This is primarily a Mk III feature, but Mk III transmitters are also capable of appending an ID to their pings.

Note 9: If -2, the receiver is not a Mk III unit (and thus does not send query pings), or the transceiver is a Mk III and no ID was appended to the query ping. Otherwise, if 0..15 that ID was appended to the interrogation ping.