Combining CAN bus streams with other sensors

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Sometimes we want to use data from other sensors in combination with data from the CAN bus. Here we will show you how to combine streams from multiple sources into a single stream.

Let's say that we have both a GPS sensor and a CAN bus and that we want to combine the GPS readings with data from the CAN bus.

Simulate a GPS sensor stream

To illustrate this we have provided a file gps-data.csv with recorded GPS values. We can simulate a GPS sensor by reading the GPS values from the file and emitting a stream of values with one measurement every 0.5 seconds.

create function gps_stream() -> Stream of Vector
  as select Stream of gps
       from Vector gps
      where gps in csv:file_stream(sa_home() +
                                   "models/canbus-guide/gps-data.csv",
                                   "read",
                                   0.5);

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You can try it by executing the following query:

gps_stream();

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Simulate a CAN bus data stream

Now we need to simulate a CAN bus stream. We'll quickly step through the queries needed. If you have read the previous chapters in this guide you'll be familiar with most steps.

First load the CAN bus model.

system_models:load("canbus");

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Translate the DBC file to OSQL format.

can:import_dbc(sa_home() + "models/canbus-guide/j1939.dbc",
               sa_home() + "models/canbus-guide/j1939_dbc.osql",
               []);

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Load the translated signal definitions.

load_osql(sa_home() + "models/canbus-guide/j1939_dbc.osql");

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Create a function that generates a data stream from a recorded CAN file.

create function j1939_can_data_stream() -> Stream of Vector
  as can:playback_socketcan(sa_home() +
        'models/canbus-guide/j1939-can-data.log');

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Create a wrapper function that makes the CAN bus emit recorded values every 0.1 seconds.

create function can_data_stream_wrapper() -> Stream of Vector
  as select stream of v
      from Vector v
      where v in heartbeat_wrap(j1939_can_data_stream(), 0.1);

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Then we need to set the CAN data source.

set bus(typenamed("can:signal")) = #'can_data_stream_wrapper';

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Now we can try our simulated CAN bus.

can:ts_signal_stream(["EEC1_EngineSpeed", "CCVS1_WheelBasedVehicleSpeed"]);

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Combining the CAN bus and GPS streams

Now we have two data streams can:ts_signal_stream() and gps_stream(). The CAN bus stream has a timestamp but we will provide new timestamps for our combined stream, so we create a wrapper function that strips the CAN bus stream of its timestamp.

create function can_stream() -> Stream of Vector
  as select Stream of can
       from Vector can, Timeval of Vector tv
      where tv in can:ts_signal_stream(["EEC1_EngineSpeed", "CCVS1_WheelBasedVehicleSpeed"])
        and can = value(tv);

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Check that you only get the CAN bus values now by executing the following query:

can_stream();

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Now we can use pivot() to combine the two streams. We create a function that combines the two streams and adds a timestamp to the resulting stream.

create function can_and_gps() -> Stream of Timeval of Vector
  as select Stream of ts(concat(can,gps))
       from Vector can, Vector gps, Vector v
      where v in pivot([can_stream(), gps_stream()], [[-1],[-1]])
        and [can, gps] = v;

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Some details of what the function does:

2: Construct the output by concatenating the CAN vector with the GPS vector and puth the result in a Timeval with ts().

4: Use pivot() to combine the stream from can_stream() with the stream from gps_stream() and use [-1] as default value for both streams (used if a stream has not emitted any value yet).

5: Use multi bind to assign can to the vector from the CAN bus stream and gps to the vector from the GPS stream.

Now try the combined stream.

can_and_gps();

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The output from can_and_gps() is a stream of Timeval where the data vector is the values from the CAN bus and GPS streams.

             ┌─── Timestamp
             │                     ┌─── EEC1_EngineSpeed
             │                     │        ┌─── CCVS1_WheelBasedVehicleSpeed
             │                     │        │           ┌─── Latitude
             │                     │        │           |         ┌─── Longitude
             ↓                     ↓        ↓           ↓         ↓
ts(|2022-03-28T19:47:22.556Z|, [1424.625,19.8046875,17.636865,59.845127])