Python Manual Vehicle Model Creation

Learn how to create a Vehicle Model manually for python

Setup a Python Package manually

A Vehicle Model should be defined in its own Python Package. This allows to distribute the Vehicle Model later as a standalone package and to use it in different Vehicle App projects.

The name of the Vehicle Model package will be my_vehicle_model for this walkthrough.

  1. Start Visual Studio Code

  2. Select File > Open Folder (File > Open… on macOS) from the main menu.

  3. In the Open Folder dialog, create a my_vehicle_model folder and select it. Then click Select Folder (Open on macOS).

  4. Create a new file setup.py under my_vehicle_model:

    from setuptools import setup
    
    setup(name='my_vehicle_model',
        version='0.1',
        description='My Vehicle Model',
        packages=['my_vehicle_model'],
        zip_safe=False)
    

    This is the Python package distribution script.

  5. Create an empty folder my_vehicle_model under my_vehicle_model.

  6. Create a new file __init__.py under my_vehicle_model/my_vehicle_model.

At this point the source tree of the Python package should look like this:

my_vehicle_model
├── my_vehicle_model
│   └── __init__.py
└── setup.py

To verify that the package is created correctly, install it locally:

pip3 install .

The output of the above command should look like this:

Defaulting to user installation because normal site-packages is not writeable
Processing /home/user/projects/my-vehicle-model
Preparing metadata (setup.py) ... done
Building wheels for collected packages: my-vehicle-model
Building wheel for my-vehicle-model (setup.py) ... done
Created wheel for my-vehicle-model: filename=my_vehicle_model-0.1-py3-none-any.whl size=1238 sha256=a619bc9fbea21d587f9f0b1c1c1134ca07e1d9d1fdc1a451da93d918723ce2a2
Stored in directory: /home/user/.cache/pip/wheels/95/c8/a8/80545fb4ff73c974ac1716a7bff6f7f753f92022c41c2e376f
Successfully built my-vehicle-model
Installing collected packages: my-vehicle-model
Successfully installed my-vehicle-model-0.1

Finally, uninstall the package again:

pip3 uninstall my_vehicle_model

Add Vehicle Models manually

  1. Install the Python Vehicle App SDK:

    pip3 install git+https://github.com/eclipse-velocitas/vehicle-app-python-sdk.git
    

    The output of the above command should end with:

    Successfully installed sdv-x.y.z
    

    Now it is time to add some Vehicle Models to the Python package. At the end of this section you will have a Vehicle Model, that contains a Cabin model, a Seatmodel and has the following tree structure:

     Vehicle
     └── Cabin
         └── Seat (Row, Pos)
    
  2. Create a new file Seat.py under my_vehicle_model/my_vehicle_model:

    from sdv.model import Model
    
    class Seat(Model):
    
        def __init__(self, parent):
            super().__init__(parent)
            self.Position = DataPointFloat("Position", self)
    

    This creates the Seat model with a single data point of type float named Position.

  3. Create a new file Cabin.py under my_vehicle_model/my_vehicle_model:

    from sdv.model import Model
    
      class Cabin(Model):
          def __init__(self, parent):
              super().__init__(parent)
              self.Seat = SeatCollection("Seat", self)
    
      class SeatCollection(Model):
          def __init__(self, name, parent):
              super().__init__(parent)
              self.name = name
              self.Row1 = self.RowType("Row1", self)
              self.Row2 = self.RowType("Row2", self)
    
          def Row(self, index: int):
              if index < 1 or index > 2:
                  raise IndexError(f"Index {index} is out of range")
              _options = {
                  1 : self.Row1,
                  2 : self.Row2,
              }
              return _options.get(index)
    
          class RowType(Model):
              def __init__(self, name, parent):
                  super().__init__(parent)
                  self.name = name
                  self.Pos1 = Seat("Pos1", self)
                  self.Pos2 = Seat("Pos2", self)
                  self.Pos3 = Seat("Pos3", self)
    
              def Pos(self, index: int):
                  if index < 1 or index > 3:
                      raise IndexError(f"Index {index} is out of range")
                  _options = {
                      1 : self.Pos1,
                      2 : self.Pos2,
                      3 : self.Pos3,
                  }
                  return _options.get(index)
    

    This creates the Cabin model, which contains a set of six Seat models, referenced by their names or by rows and positions:

    • row=1, pos=1
    • row=1, pos=2
    • row=1, pos=3
    • row=2, pos=1
    • row=2, pos=2
    • row=2, pos=3
  4. Create a new file vehicle.py under my_vehicle_model/my_vehicle_model:

    from sdv.model import Model
    from my_vehicle_model.Cabin import Cabin
    
    
    class Vehicle(Model):
        """Vehicle model"""
    
        def __init__(self, name):
            super().__init__()
            self.name = name
            self.Speed = DataPointFloat("Speed", self)
            self.Cabin = Cabin("Cabin", self)
    
    vehicle = Vehicle("Vehicle")
    

The root model of the Vehicle Model tree should be called Vehicle by convention and is specified, by setting parent to None. For all other models a parent model must be specified as the 2nd argument of the Model constructor, as can be seen by the Cabin and the Seat models above.

A singleton instance of the Vehicle Model called vehicle is created at the end of the file. This instance is supposed to be used in the Vehicle Apps. Creating multiple instances of the Vehicle Model should be avoided for performance reasons.

Add a Vehicle Service

Vehicle Services provide service interfaces to control actuators or to trigger (complex) actions. E.g. they communicate with the vehicle internals networks like CAN or Ethernet, which are connected to actuators, electronic control units (ECUs) and other vehicle computers (VCs). They may provide a simulation mode to run without a network interface. Vehicle Services may feed data to the Data Broker and may expose gRPC endpoints, which can be invoked by Vehicle Apps over a Vehicle Model.

In this section, we add a Vehicle Service to the Vehicle Model.

  1. Create a new folder proto under my_vehicle_model/my_vehicle_model.

  2. Copy your proto file under my_vehicle_model/my_vehicle_model/proto

    As example you could use the protocol buffers message definition seats.proto provided by the KUKSA VAL services which describes a seat control service.

  3. Install the grpcio tools including mypy types to generate the python classes out of the proto-file:

    pip3 install grpcio-tools mypy_protobuf
    
  4. Generate Python classes from the SeatService message definition:

    python3 -m grpc_tools.protoc -I my_vehicle_model/proto --grpc_python_out=./my_vehicle_model/proto --python_out=./my_vehicle_model/proto --mypy_out=./my_vehicle_model/proto my_vehicle_model/proto/seats.proto
    

    This creates the following grpc files under the proto folder:

    • seats_pb2.py
    • seats_pb2_grpc.py
    • seats_pb2.pyi
  5. Create the SeatService class and wrap the gRPC service:

    from sdv.model import Service
    
    from my_vehicle_model.proto.seats_pb2 import (
        CurrentPositionRequest,
        MoveComponentRequest,
        MoveRequest,
        Seat,
        SeatComponent,
        SeatLocation,
    )
    from my_vehicle_model.proto.seats_pb2_grpc import SeatsStub
    
    
    class SeatService(Service):
        "SeatService model"
    
        def __init__(self):
            super().__init__()
            self._stub = SeatsStub(self.channel)
    
        async def Move(self, seat: Seat):
            response = await self._stub.Move(MoveRequest(seat=seat), metadata=self.metadata)
            return response
    
        async def MoveComponent(
            self,
            seatLocation: SeatLocation,
            component: SeatComponent,
            position: int,
        ):
            response = await self._stub.MoveComponent(
                MoveComponentRequest(
                    seat=seatLocation,
                    component=component,  # type: ignore
                    position=position,
                ),
                metadata=self.metadata,
            )
            return response
    
        async def CurrentPosition(self, row: int, index: int):
            response = await self._stub.CurrentPosition(
                CurrentPositionRequest(row=row, index=index),
                metadata=self.metadata,
            )
            return response
    

    Some important remarks about the wrapping SeatService class shown above:

    • The SeatService class must derive from the Service class provided by the Python SDK.
    • The SeatService class must use the grpc channel from the Service base class and provide it to the _stub in the __init__ method. This allows the SDK to manage the physical connection to the grpc service and use service discovery of the middleware.
    • Every method needs to pass the metadata from the Service base class to the gRPC call. This is done by passing the self.metadata argument to the metadata of the gRPC call.
Last modified January 17, 2023: Changed overview picture (#51) (ea5274b)