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Old 24-09-2018, 02:34   #1
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recording depths with GPS positions for bathymetry

Greetings dear forum users:

The situation:

I want to record echosounder depths with GPS points for a bathymetric survey. This way, I can process them in QGIS vai a gpx file or whatnot. But I don't want to spend thousands of bux for survey equipment, and I probably don't want an all-in-one fishfinder solution (which can usually do this kind of thing in my limited experience) because I already have a fancy GPS, and the all-in-one solutions usually have a really wide beam depth transducer; I want a narrow beam; and I want to be able to import custom made route file gpx I've made in QGIS, which isn't always supported so well.

The Questions:

-If I plug in a transducer and GPS into OpenCPN via NMEA, will the depth automatically get added to GPS trackpoints when I record a track? Or do I need this thing called a multiplexer? (I see there are hardware of software solutions for that)

-Do I need the hydrographic survey plugin for this?
Hydrographic Survey Plugin

-Can I adjust the spacing of trackpoints in recorded tracks? In the tracks I've tried making with OpenCPN it seems like the interval is 30 seconds... I'd like it to be closer so I can get 10m spacing intervals or less. What determines how often these trackpoints are made?


I'd also be fine with just getting a log with tonnes of echosounder depths if they have a timestamp which I could then match up to GPS trackpoints by writing myself a little script or whatever later when I'm doing the data processing. But I still need to make sure I get enough GPS points rather than just 30 seconds.

I appreciate any advice or tips; thanks!
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Old 24-09-2018, 03:21   #2
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Re: recording depths with GPS positions for bathymetry

You can use something called voyage data recorder plugin. It will record all NMEA messages received by O regardless of the source device. Later you can write a simple tool (Python is a good choice) to extract the position and depth data. Be aware that high speed can obscure the relationship between depth location and GPS coordinate. This idea requires a lot of special sensors if the boat will be traveling at 30 knots.
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Old 24-09-2018, 05:13   #3
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Re: recording depths with GPS positions for bathymetry

Quote:
Originally Posted by transmitterdan View Post
You can use something called voyage data recorder plugin. It will record all NMEA messages received by O regardless of the source device. Later you can write a simple tool (Python is a good choice) to extract the position and depth data. Be aware that high speed can obscure the relationship between depth location and GPS coordinate. This idea requires a lot of special sensors if the boat will be traveling at 30 knots.
Thank you transmitterdan. I'll look into the vdr plugin... it could work as long as it records the depth sounding with a timestamp so i can match it to the GPS timestamp.

I intend to do it pretty slowly (5kt or less) and in a grid in the form of a gpx route.

Still though, I'm not quite sure how to make OpenCPN record more GPS points into the tracklog, but perhaps vdr plugin keeps a log of all the gps fixes that OpenCPN doesn't bother adding to the track.
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Old 24-09-2018, 06:29   #4
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recording depths with GPS positions for bathymetry

The depth data has no time stamp in NMEA format. But the depth readings will be surrounded by GPS messages that include time so one can infer the time of the depth readings.

VDR plugin records all data.
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Old 24-09-2018, 07:14   #5
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Re: recording depths with GPS positions for bathymetry

Quote:
Originally Posted by hydro_explorer View Post
Thank you transmitterdan. I'll look into the vdr plugin... it could work as long as it records the depth sounding with a timestamp so i can match it to the GPS timestamp.

I intend to do it pretty slowly (5kt or less) and in a grid in the form of a gpx route.

Still though, I'm not quite sure how to make OpenCPN record more GPS points into the tracklog, but perhaps vdr plugin keeps a log of all the gps fixes that OpenCPN doesn't bother adding to the track.
There's a sample VDR file on the manual page, just under "want to play?" -
https://opencpn.org/wiki/dokuwiki/do...ugins:logs:vdr

The VDR just records raw NMEA sentences (afaik) and don't think any of the DB* NMEA depth sentences have a timestamp so you might need to get the time from a nearby GPS sentence, most GPS's send about 1Hz ISTR so should be under a second out worst case. (Edit - took a while to hit send - T.dan got there first )

If you haven't come across it before, node-red can make stripping out data from files quick and easy.

This took a few minutes and will read a file then send the last GPS time before a depth message then the depth comma separated.
"062314,0060.4"

Code:
[
    {
        "id": "21769b7b.1a1064",
        "type": "inject",
        "z": "c9647b2e.674eb8",
        "name": "",
        "topic": "",
        "payload": "",
        "payloadType": "date",
        "repeat": "",
        "crontab": "",
        "once": false,
        "onceDelay": 0.1,
        "x": 100,
        "y": 320,
        "wires": [
            [
                "a09b1cd0.0d1ba"
            ]
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    },
    {
        "id": "a09b1cd0.0d1ba",
        "type": "file in",
        "z": "c9647b2e.674eb8",
        "name": "",
        "filename": "C:\\Users\\PaddyB\\Downloads\\deleteMe\\rausch_shortened.txt",
        "format": "lines",
        "chunk": false,
        "sendError": false,
        "x": 260,
        "y": 400,
        "wires": [
            [
                "414a5c71.7097d4"
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        "type": "switch",
        "z": "c9647b2e.674eb8",
        "name": "",
        "property": "payload",
        "propertyType": "msg",
        "rules": [
            {
                "t": "regex",
                "v": "GLL",
                "vt": "str",
                "case": false
            },
            {
                "t": "regex",
                "v": "DBT",
                "vt": "str",
                "case": false
            }
        ],
        "checkall": "true",
        "repair": false,
        "outputs": 2,
        "x": 150,
        "y": 520,
        "wires": [
            [
                "ce2784ba.437c08"
            ],
            [
                "63c7da01.e73f04"
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    },
    {
        "id": "ce2784ba.437c08",
        "type": "function",
        "z": "c9647b2e.674eb8",
        "name": "",
        "func": "var splitString = msg.payload.split(',');\nmsg.payload = splitString[5];\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "x": 330,
        "y": 500,
        "wires": [
            [
                "3e32cdfb.aa1362"
            ]
        ]
    },
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        "id": "63c7da01.e73f04",
        "type": "function",
        "z": "c9647b2e.674eb8",
        "name": "",
        "func": "var splitString = msg.payload.split(',');\nmsg.payload = splitString[3];\nmsg.payload = flow.get(\"timestamp\") + \",\" +  msg.payload;\nreturn msg;",
        "outputs": 1,
        "noerr": 0,
        "x": 310,
        "y": 560,
        "wires": [
            [
                "fd363eb.b17f0c"
            ]
        ]
    },
    {
        "id": "3e32cdfb.aa1362",
        "type": "change",
        "z": "c9647b2e.674eb8",
        "name": "",
        "rules": [
            {
                "t": "set",
                "p": "timestamp",
                "pt": "flow",
                "to": "payload",
                "tot": "msg"
            }
        ],
        "action": "",
        "property": "",
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        "reg": false,
        "x": 530,
        "y": 460,
        "wires": [
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        "z": "c9647b2e.674eb8",
        "name": "",
        "active": true,
        "tosidebar": true,
        "console": false,
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        "complete": "true",
        "x": 610,
        "y": 580,
        "wires": []
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    {
        "id": "3f9fffe4.a4baa",
        "type": "debug",
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        "active": false,
        "tosidebar": true,
        "console": false,
        "tostatus": false,
        "complete": "true",
        "x": 730,
        "y": 400,
        "wires": []
    }
]
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Old 24-09-2018, 09:21   #6
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Re: recording depths with GPS positions for bathymetry

If you can't get OCPN plug-ins to do what you want (and you probably can), some people are using NavMonPc do depth surveys by recording time, depth, and lat/lon once per second in the spreadsheet-format log. You can then do what you wish with the logfile. You are on your own when it comes to tide height though.
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Old 24-09-2018, 09:46   #7
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Re: recording depths with GPS positions for bathymetry

Quote:
Originally Posted by conachair View Post
........ and will read a file then send the last GPS time before a depth message then the depth comma separated.
"062314,0060.4"
.........
Which is a silly way to go about it

It's lat & long you want, so record in VDR with gps update rate set high then make a file from lat, long & next depth reading.
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Old 25-09-2018, 08:10   #8
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Re: recording depths with GPS positions for bathymetry

CPN does not write depth data in the track

Hydrographic Survey Plugin has the ability to record depth marks at a specified distance. There is no time.
Export is possible in XYZ format

I think it will be easier for you to use a ready solution for non-professional hydrography https://reefmaster.com.au

Now the chartplotters Garmin, Lowrance, Hymminbird can build a bathymetric depth map in real time on the screen
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Old 25-09-2018, 08:35   #9
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Re: recording depths with GPS positions for bathymetry

I have great interest in providing support to opencpn to automatically generate chart (with contours) in real time. The issue is, I do not have depth sounder with nmea data output. So for this project I managed to build my own depth sounder, but it is still experimental.

The advantage is, I have far more control over how the depth sounder works through the free software that drives it. I can use different transducers etc.. but as stated, it is still an experiment and I have not the time to complete it yet.
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Old 25-09-2018, 10:36   #10
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Re: recording depths with GPS positions for bathymetry

I am also interested in the possibility of constructing bathymetric maps in real time.
If something like this is done



is ready to make a financial contribution to the equipment and development or refinement of the hydrographic plug-in
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