Load a recording

1. Two kinds of recording

The difference between the two kinds applies to the whole app. Read these two definitions first.

• AIS data gives the track of each vessel. Ships broadcast their positions and identities over AIS. A receiver, a logger, or an export from an authority captures these broadcasts. AIS data tells you where each vessel was and who each vessel was. It is the traffic picture.
• VDR data is the output of a voyage data recorder. It carries the same AIS traffic plus the instrument stream of the recording ship. That stream is raw NMEA across the serial channels of the VDR: GPS, gyro, engine, rudder and alarms. VDR data also carries bridge audio in many cases. It is the full picture from the bridge of one vessel.

This extra own-ship stream is the reason that some features need VDR data. The decode rules and the installation profile both work on those instrument channels. A plain AIS recording does not have those channels. All the other features work with either kind of recording: tracks, playback, CPA, notes and exports.

2. Open a file

Click Open file in the header. It accepts one or more recordings. Stingray finds the format itself, so you do not select a type. Stingray reads plain CSV and six NMEA packaging dialects (from bare AIVDM to the Wärtsilä VDR wrapper and the NMEA 4.10 tag blocks). The reference has the full list and shows the form of each dialect on disk.

The CSV importer accepts many different column names. It recognizes the usual spellings of the fields that it needs:

Stingray also re-imports its own decoded-data CSV without errors. The CSV is therefore an interchange format between sessions or between tools.

3. Load a whole VDR folder

A VDR dump is rarely one file. It is usually a folder of per-minute or per-hour logs, sometimes in ZIP archives, with configuration files and audio.

Click Open VDR folder to load the full folder. Stingray scans the folder and classifies each file. It calculates the time span of each file from the first-line timestamp and from the filename. Stingray then lets you select a time window before the load. Thus you can reduce a multi-day archive to the hour around an incident. Stingray parses only the files in that window.

The time window controls all the data that follows. The vessels, the own-ship readings and the load report describe only the window that you selected. They do not describe the whole archive. Stingray also flags the files that are probably configuration documents. It shows them for the installation profile and for the decode-rules draft, so that you know which files to supply.

4. Salvage mode

Some VDRs write their NMEA inside a proprietary binary container for which Stingray has no adapter. Stingray does not refuse such a file, but changes to salvage mode. In salvage mode Stingray scans all the bytes, text or binary. It recovers each sentence that has a valid NMEA checksum. The checksum is the test that accepts a sentence. A random run of bytes that is similar to a sentence does not pass that test.

5. The load report

Each load ends with a report of what Stingray found. The report shows the data that Stingray decoded and also the data that Stingray could not decode. It groups the sentence formatters by the level of interpretation:

• AIS. These are the vessel-position messages and the static messages.
• Decoded. These are own-ship sensor sentences with a published field layout. Stingray reads them into real values.
• Code tables. Stingray recognizes these coded sentences. Their meaning needs your decode rules.
• Opaque. These are proprietary or non-standard sentences. Stingray counts them but does not interpret them.

The report also shows the caveats that are important for a forensic read. It shows a salvage notice. It gives a count of the long-range (type 27) reports that Stingray counted but did not plot. It shows the safety-related text messages (types 12 and 14) with their sender, their addressee and their time. Stingray shows those messages at load time only and never saves them with the project. The report also gives a count of the physically implausible positions that Stingray dropped.

For a VDR, the report shows which own-ship MMSI the sensor track linked to. If more than one own-ship MMSI appeared, the report flags this. Stingray drops no data without a record. If Stingray does not interpret a sentence type, the report says so. If Stingray discards a fix, the report says so.

Not every AIS transmitter is a ship. The report tells you how Stingray treated each kind. Stingray keeps shore base stations as fixed marks at their broadcast (type 4) position. It shows them as muted triangles with their own display toggle. It excludes them from the vessel fleet and from the counts of moving traffic.

Stingray keeps the AtoN navigation marks: the buoys and beacons, and also the virtual wreck marks. It keeps the name and the position that their type-21 reports broadcast. Those marks give the charted context against which you judge an incident.

Stingray keeps the distress transponders (SART, man-overboard and EPIRB). It flags them clearly and shows the time window in which the recording contains them. A true distress transponder in a recording is the incident.