ROV CTD Zero MQ Client

Message Structure

The data coming from the CTD is parsed into the following fields

Variable	Data Type
temperature	real
conductivity	real
pressure	real
analog1	real
analog2	real
analog3	real
analog4	real
sound_velocity	real
in_water	bool
receiving_data	bool

When you subscribe to the ZeroMQ proxy, you will want to subscribe to SEABIRD_CTD_MSG.

Python

Here is an example script to subscribe to the ROV CTD messages coming over ZeroMQ (note you need the python ZMQ module installed in your Python environment)

# Import ZeroMQ module
import zmq
import json
from datetime import datetime

# ZMQ Channel. Some common channels are:
ZMQ_CHANNEL = "SEABIRD_CTD_MSG"

# A function to flatten the json data
def flatten_json(json_string):
    # The JSON object to return
    out = {}

    # Convert the string to JSON object
    json_object = json.loads(json_string)

    # Load the top level properties
    if "lcm_channel" in json_object:
        out["lcm_channel"] = json_object["lcm_channel"]
    if "message_type" in json_object:
        out["message_type"] =  json_object["message_type"]
    if "num_integers" in json_object:
        out["num_integers"] = json_object["num_integers"]
    if "num_reals" in json_object:
        out["num_reals"] = json_object["num_reals"]
    if "pub_id" in json_object:
        out["pub_id"] = json_object["pub_id"]
    if "pub_sequence" in json_object:
        out["pub_sequence"] = json_object["pub_sequence"]
    if "pub_timestamp" in json_object:
        out["pub_timestamp"] = json_object["pub_timestamp"]
    if "integer_list" in json_object:
        for integer_object in json_object['integer_list']:
            out[integer_object['key']] = integer_object['value']
    if "real_list" in json_object:
        for real_object in json_object['real_list']:
            out[real_object['key']] = real_object['value']
    if "string_list" in json_object:
        for string_object in json_object['string_list']:
            out[string_object['key']] = string_object['value']
    if "boolean_list" in json_object:
        for boolean_object in json_object['boolean_list']:
            out[boolean_object['key']] = boolean_object['value']
    return out

# Change these to point to your server and port
host = "coredata-rcsn.rc.mbari.org"
port = "5556"

# Creates a subscriber socket instance
context = zmq.Context()
socket = context.socket(zmq.SUB)

# Connects to a bound socket
socket.connect("tcp://{}:{}".format(host, port))

# Subscribes to all topics
socket.subscribe(ZMQ_CHANNEL)

# Receives a multipart message
while(True):
    the_response = socket.recv_multipart()
    payload_s = the_response[-1].decode("utf-8", errors="strict")
    data = flatten_json(payload_s)
    print(json.dumps(data, indent=4))
    # Convert the timestamp to a human-readable format
    human_readable_date = datetime.fromtimestamp(data['pub_timestamp']).strftime('%Y-%m-%d %H:%M:%S')