Recent Posts

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11
AIS Dispatcher / Display Vessel name in Google Earth
« Last post by kaitahmak on 04 April, 2017, 07:11:24 am »
hi All ,

I have AIS Dispatcher running with Google earth connected as a network link - The data come in and displays on the map fine - but it does not show the vessel name. It does in the data on the side bar. Any ideas how I get it to show on the map above the vessels ?  Like it does with the Google Earth feed from Vessel Tracker <see attached>
12
General Discussion / Rate of Turn data
« Last post by maclausen on 31 March, 2017, 04:59:11 pm »
Good day;

In the on line description, the data from the web service should include Rate of Turn (ROT) when requesting data in AIS format.  However, I don't see this value being returned in either .xml or .csv formats.   And I'm sure I'm seeing Class A reports in the downloaded data, just without the rate of turn field.

This question was posed last year, but I had not seen a response. 

Can anyone offer any guidance?

Cheers!
13
Ah good deal.. (I chose wisely)
I implemented the '@' sign as a character string termination in my Java code. (the '@' sign and anything past it is dropped)
I've run a lot of well formed sentences/messages through my code but testing with 'real world' malformed sentences has proven difficult and has me concerned.
I feel a little better now.

Thanks for help
Much appreciated.
TR.Martin
14
The @ character is not terminator, but rather a fill character to pad out fixed-length string fields. Decoding software would treat the first @ as a terminator, but encodng software must fill out fixed-length strings with trailing @ characters
15
The ITU spec (Recommendation ITU-R M.1371-5) doesn't describe using the at-sign (@ representing six-zero-bits) as a terminator in text fields.

Nonetheless, Eric has likely seen devices using the at-sign as such in the wild, so there is field experience speaking in his advice.

I suspect this situation would have been the result of poorly-written C-language code in which character strings were terminated in a byte of zeros.  Commonly this byte would be followed by garbage in the buffer -- whatever was previously present in the larger buffer.  When a C string is copied into a bigger buffer as part of data that will be transmitted then these trailing bytes should have been overlaid with zeros.

The DMA Java AIS library, which I use, indeed treats the at-sign as a terminator:

/**
     * Utility to trim text from AIS message
     *
     * @param text
     * @return
     */
    public static String trimText(String text) {
        if (text == null) {
            return null;
        }
        // Remove @
        int firstAt = text.indexOf("@");
        if (firstAt >= 0) {
            text = text.substring(0, firstAt);
        }
        // Trim leading and trailing spaces
        return text.trim();
    }


So this seems to be a pragmatic de facto standard approach.

Best,
Gary
16
From the standard (1):

"Character strings are presented left to right most significant bit first. All unused characters should be
represented by the @ symbol, and they should be placed at the end of the string."

(1) http://www.itu.int/dms_pubrec/itu-r/rec/m/R-REC-M.1371-5-201402-I!!PDF-E.pdf
17
Software development / Is the @ sign a terminator for the Character String fields?
« Last post by trmartin on 24 March, 2017, 10:32:00 pm »
This is a pretty simple question: in Eric Raymond's AIVDM/AIVDO protocol decoding page just below the six bit ASCII table (Table 3) he makes a statement that the @ sign (0x00) is used to terminate AIS Character String fields. Fair enough, However I cannot verify this action anywhere else.

So I thought someone here might shed some light on this? any input would be helpful...

Cheers,
TR.Martin
18
AIS Dispatcher / Tracking a handful of vessels on Google Map via kml
« Last post by Ventilator on 21 March, 2017, 04:08:22 pm »
Hello everyone. I'm working on a website for an oceanographic project.

The project uses a few vessels, which are on research voyages for much of the year, and for which I have MMSI references.

We have a Google Map on the site, with a few layers, drawing from .kml files. I'd like to display the live position of the vessels on this map, and I wonder if AIS Dispatcher can help.

Would someone be able to suggest whether this is indeed possible, and if so what the best practice for establishing an updating .kml file from ship data might be?

Many thanks, in advance, for your assistance

Ventilator
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AIS Decoder / AIS decoder install with libasound2-dev
« Last post by Nicolas on 21 February, 2017, 09:43:11 pm »
Hi
When I try to install aisdecoder on a raspeberry pi3 with desbian (new version) I<m not able to get libasound-dev. No choice to install older version than libasound2-dev
Is anyone can help me please

pi@raspberrypi:~/aisdecoder/build $ sudo cmake ../ -DCMAKE_BUILD_TYPE=Release
-- Build configuration: Release
CMake Error at CMakeLists.txt:54 (MESSAGE):
  The development files for ALSA or PulseAudio are required - libasound-dev,
  libpulse-dev


-- Configuring incomplete, errors occurred!
See also "/home/pi/aisdecoder/CMakeFiles/CMakeOutput.log".
See also "/home/pi/aisdecoder/CMakeFiles/CMakeError.log".
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AIS Hardware / Simple AIS Receiver for Linux / Mac
« Last post by tayljordan on 20 February, 2017, 05:30:39 am »
I'm sure this has been asked a thousand times but what is the simplest way to get up and running receiving AIS on a linux / mac machine? I need a home-based unit and will be looking to collect data that I can work with in Python.

I live in the San Francisco Bay Area. So far all I can come up with is a dASIy with a Raspberry Pi. Is that good enough?

Thanks in advance.
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