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ATLAS

The ATLAS format is a fixed-length binary protocol used as the default motion sensor output for Atlas Fansweep echo sounders.

Data:

  • Roll, pitch

  • Heave

Format:

<DLE><Rr><Pp><Hh><Q><DLE>

ATLAS Fansweep 20 protocol description

FIELD N.

FIELD

DESCRIPTION

UNIT

DATA TYPE

NOTE

Byte 0

DLE

start character


-

HEX

Control character: 0x10. Used to indicate the start of the message.

Byte 1-2

R

roll MSB


[deg]


U16

Range: [0, 360] deg.

Resolution: 360/2^16 degrees per bit.

r

roll LSB

Byte 3-4

P

pitch MSB


[deg]


U16

Range: [270, 90] deg.

Resolution: 360/2^16 degrees per bit.

p

pitch LSB

Byte 5-6

H

heave MSB



[mm]



I16

Sign: Positive (+) when elevated.

Range: [-32767, 32766] mm.

Resolution: 1 mm per bit.

h

heave LSB

Byte 7

Q

status code from 0 to 7

-

U8

See status table below for details.

Byte 8

DLE

stop character


-

HEX

Control character: 0x10. Used to indicate the end of the message.

Status code:

ATLAS status code description

STATUS CODE

DESCRIPTION

NOTE

0

unaided, stable data

The MRU operates without external input and provides stable data.

1

unaided, unstable data.

No external input is used, and the data is unstable, likely due to alignment after power-on or restart.

2

speed aided, stable data.

The MRU uses external speed data and provides stable measurements.

3

speed aided, unstable data

The MRU receives external speed data, but its output is unstable, likely due to alignment after power on, or input of speed data.

4

heading aided, stable data

The MRU uses external heading data and provides stable measurements.

5

heading aided, unstable data

The MRU receives external heading data, but its output is unstable, likely due to alignment after power on, or input of heading data.

6

full aided, stable data.

The MRU uses both speed and heading data as external inputs and provides stable measurements.

7

full aided, unstable data.

The MRU operates with external speed and heading data, but the output is unstable, likely due to alignment after power on, or input of aiding data.

Example:

ATLAS frame with raw example data is listed below.

Byte 0

Byte 1

Byte 2

Byte 3

Byte 4

Byte 5

Byte 6

Byte 7

Byte 8

0x10

0x1E

0x85

0x0F

0xA0

0x12

0x34

0x02

0x10

Decode raw U16 values from the ATLAS frame above to get roll, pitch and heave by using hex-to-decimal conversion and the resolution.

  • Roll calculation

    • Resolution: 360/2^16 degrees per bit = 0.005493164 degrees per bit.

    • Roll U16 value (big-endian): (0x1E x 256) + 0x85 = (30 x 256) + 133 = 7813.

    • Roll angle = roll U16 value x resolution = 7813 x 360/2^16 degrees = 42.92 degrees.

  • Pitch calculation

    • Resolution: 360/2^16 degrees per bit = 0.005493164 degrees per bit.

    • Pitch U16 value (big-endian): (0x0F x 256) + 0xA0 = (15 x 256) + 160 = 4000.

    • Pitch angle = pitch U16 value x resolution = 4000 x 360/2^16 degrees = 21.97 degrees.

  • Heave calculation

    • Resolution: 1 mm per bit.

    • Heave U16 value (big-endian): (0x12 x 256) + 0x34 = (18 x 256) + 52 = 4660.

    • Heave = heave U16 value x resolution = 4660 x 1 mm = 4.66 m.

  • Status code

    • Status code: 0x02 = 2.

    • This refers to status code 2: speed aided, stable data.


Note 1

Atlas follows big-endian format: MSB is stored at the lowest memory address, followed by the LSB.

Note 2

The reference frame for data (e.g., heave) is configurable in the ATLAS protocol. Also, the data's location (e.g., MRU or MP1) is configurable.