$USRTH Receiver-Transmitter Relative Angles Message
The USRTH message provides the basic information needed to find the ROV relative to the location of an ROVL receiver. It is the message typically sent by baseline (non-Omniscan) ROVLs.
Example $USRTH message:
$USRTH,0.0,-0.0,0.0,100.0,45.0,45.0,-0.1,-0.4,-0.4,45.0,45.0,76,T,F,153,CIMU,A,-2,-2,*11
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 (ENU) [Note 1, 4]
ac: apparent bearing to transmitter in Compass degrees (NED) [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 (ENU) [Note 2, 4]
cb: true bearing to transmitter in Compass degrees (NED) [Notes 1, 4]
te: true elevation to transmitter in degrees [Note 2]
er: Euler roll angle of sensor frame, in Math degrees (ENU) [Note 3]
ep: Euler pitch angle of sensor frame, in Math degrees (ENU) [Note 3]
ey: Euler yaw (heading) angle of sensor frame, in Math degrees (ENU) [Note 3, 4]
ch: compass heading in Compass degrees (NED) [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: [IDs are a deprecated feature as of 1/1/25] 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.
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