Getting Started with OpenZen

Overview

OpenZen allows to access many different sensor models which are connected via different transports layers with one unified programming interface. This allows to develop applications which support a wide range of sensors and allows to easily adapt your application to new or additional sensors.

The following section will walk you through the process of accessing, configuring and streaming data from
a sensor connected to OpenZen. If you prefer to study and run a full code example, please have a look
at this example source file.

IO Systems

To communicate with the sensor hardware, OpenZen provides multiple so-called IO systems. Each of these can establish the communication to sensors and can list the available sensor hardware. Here are some examples of IO systems available in OpenZen:

• USB virtual COM port

• USB Express

• Bluetooth

• Network streaming

You can find the full list of available IO systems in the section [io systems].

Sensor Components

A sensor can have multiple components which supply various types of sensor data. Once the connection
to a sensor has been established, the available components can be queried and their properties can
be access and modified. Furthermore, the streaming of measurement data can be started for each component.

At this time OpenZen supports the following components:

Inertial Measurement Unit (IMU)

Provides accelerometer and gyroscope measurements and the orientation result from the sensor fusion running on the connected sensor.

Global Navigation Satellite System (GNSS)

Provides global position measurements via GPS, BeiDou, GLONASS and Galileo, the associated error estimates and information on the quality and mode of the GNSS fix.

Creating an OpenZen Client

The following description will use the C++ interface to OpenZen but other language bindings use the same concepts
described here. To see the description how to use the other language bindings, please have a look at the respective
section for the language you are interested in.

In order to acquire sensor access via OpenZen, you first need to create an OpenZen client. This can be done with the
utility method zen::make_client. This call returns an instance of the ZenClient class:

auto clientPair = zen::make_client();
auto& clientError = clientPair.first;
auto& client = clientPair.second;

if (clientError)
    // error when creating OpenZen client
    return clientError;

Receiving Events from OpenZen

Every ZenClient instance contains its own event queue which accumulates events
from all sensors that were obtained on that client. Events can either be polled
using ZenClient::pollNextEvent or waited for using ZenClient::waitForNextEvent.
The only way to terminate a client that is waiting for an event, is by destroying
the client or preemptively calling ZenClient::close.

.. this maybe explain how to setup an event loop here ?

Listing Available Sensors

The IO systems available on your platform can automatically list all available
sensors connected to the system. In order to do this, you need to call the method
ZenClient::listSensorsAsync to start the query for available sensors. Depending
on the IO systems, it can take a couple of seconds for the listing to be complete.

if (auto error = client.listSensorsAsync())
{
    // error while listing available senors
    return error;
}

The ZenClient::listSensorsAsync method will return immediately and
the information on the found sensors will be send to ZenClient's event queue and
can be retrieved with calls to ZenClient::pollNextEvent or
ZenClient::waitForNextEvent. You can either do this on your applications main
thread or use a background thread to retrieve the event listing data.

The following code snippets shows an example how to receive the OpenZen events
which contain the information during the sensor discovery process.

If the event.component.handle is 0, the event is not specific to a sensor
but an event which is related by the OpenZen client itself, like the sensor
discovery events. Next, we can check the event.eventType field for the
ZenSensorEvent_SensorFound and ZenSensorEvent_SensorListingProgress
event types. For the ZenSensorEvent_SensorFound event, the field
event.data.sensorFound is of type ZenSensorDesc which contains the
sensor's name, serial number and all information required to connect to the sensor.

bool listingComplete = false;
while (!listingComplete) {
    const auto pair = client.waitForNextEvent();
    const bool success = pair.first;
    auto& event = pair.second;
    if (!success)
        break;

    if (!event.component.handle)
    {
        switch (event.eventType)
        {
        case ZenEventType_SensorFound:
            std::cout << "Found sensor " << event.data.sensorFound.name << std::endl;
            break;

        case ZenEventType_SensorListingProgress:
            std::cout << "Sensor listing progress " << event.data.sensorListingProgress.progress
                << " %" << std::endl;
            if (event.data.sensorListingProgress.complete) {
                listingComplete = true;
            }
            break;
        }
    }
}

Connecting to a Sensor

A sensor found by the ZenClient::listSensorsAsync call can be connected via the OpenZen
client using the ZenSensorDesc which is contained in the event.data.sensorFound of
the ZenSensorEvent_SensorFound. The method call to ZenClient::obtainSensor returns a
std::pair where the first entry is a possible error code and the second entry is an
instance of the object zen::ZenSensor which can be used to access the Sensor's
properties.

auto sensorPair = client.obtainSensor(sensorDesc);
auto& obtainError = sensorPair.first;
auto& sensor = sensorPair.second;
if (obtainError)
{
    // error while obtaining the sensor
    return obtainError;
}

Sensors can also connected directly if the IO system they are connected too and their
name is known already. Here, the method ZenClient::obtainSensorByName can be called
with the name of the IO system and the name of the sensor:

// connect the sensor with the name lpmscu2000573 via the SiLabs USB IO System
auto sensorPair = client.obtainSensorByName("SiUsb", "lpmscu2000573", 921600);
auto& obtainError = sensorPair.first;
auto& sensor = sensorPair.second;
if (obtainError)
{
    // error while obtaining the sensor
    return obtainError;
}

Please check the documentation in the section :ref:io-system-label. for the available
IO systems and which naming conventions they use to identify connected sensors.

You can connect multiple sensor via one ZenClient and the events of all
sensor will be available on the event queue of the ZenClient instance.

Reading and Modifying Sensor Properties

OpenZen allows to read an modify the properties of connected sensors. Which properties
are available depends on the concrete sensor connected. You can find more information
on sensor properties in the section ref:supported-sensors-label.

Each sensor property in OpenZen has a specific data type and the respective method needs
to be used on the zen::ZenSensor instance.

auto sensorModelPair = sensor.getStringProperty(ZenSensorProperty_SensorModel);
auto & sensorModelError = sensorModelPair.first;
auto & sensorModelName = sensorModelPair.second;
if (sensorModelError) {
    // error while reading the string property from the sensor
    return sensorModelError;
}
std::cout << "Sensor Model: " << sensorModelName << std::endl;

Accessing Sensor Components

To access a specific component of a sensor, the method call ZenSensor::getAnyComponentOfType
can be used to retrieve the component of a specific type. If this component is not available
on this sensor, an error will be returned.

auto imuPair = sensor.getAnyComponentOfType(g_zenSensorType_Imu);
auto& hasImu = imuPair.first;
auto imu = imuPair.second;

if (!hasImu)
{
    // error, this sensor does not have an IMU component
    return ZenError_WrongSensorType;
}

As with the ZenSensor class the ZenSensorComponent returned by ZenSensor::getAnyComponentOfType
call can be used to access and modify the properties of the sensor component.

Reading Sensor Values

To start receiving data from a connected sensor, you need to ensure that the sensor
is in streaming mode to send out data on its own:

if (auto error = imu.setBoolProperty(ZenImuProperty_StreamData, true))
{
    // cannot set sensor into streaming mode
    return error;
}

Now, sensor events with measurement data will be available on the event queue of the OpenZen client.
You can use the previously introduced methods ZenClient::pollNextEvent or
ZenClient::waitForNextEvent to retrieve the sensor data of the inertial measurement unit:

const auto pair = client.waitForNextEvent();
const bool success = pair.first;
auto& event = pair.second;
if (!success)
    break;

// ensure the event is from the IMU component
if (event.component.handle == imu.component().handle)
{
    switch (event.eventType)
    {
    case ZenEventType_ImuData:
            std::cout << "> Acceleration: \\t x = " << event.data.imuData.a[0]
                << "\\t y = " << event.data.imuData.a[1]
                << "\\t z = " << event.data.imuData.a[2] << std::endl;
            
            // take note that in some sensors the gyro data is stored in g2
            // check the table below for details
            std::cout << "> Gyro: \\t\\t x = " << event.data.imuData.g[0]
                << "\\t y = " << event.data.imuData.g1[1]
                << "\\t z = " << event.data.imuData.g1[2] << std::endl;
        break;
    }
}

.. list-table:: Sensors and its gyro key name
:header-rows: 1

• • Field name

  • IG1 / IG1P

  • LPMS3

  • NAV3

  • BE / ME

• • g1

  • o

  • x

  • o

  • x

• • g2

  • o

  • o

  • x

  • o

To process the GNSS data streamed from the sensor, you can filter for events coming from
the GNSS component like this:

if (event.component.handle == g_gnssHandle)
{
    switch (event.eventType)
    {
    case ZenEventType_GnssData:
            std::cout << "> GPS Fix Type: \\t = " << event.data.gnssData.fixType << std::endl;
            std::cout << "> Longitude: \\t = " << event.data.gnssData.longitude
                << "   Latitude: \\t = " << event.data.gnssData.latitude << std::endl;
        break;
    }
}

.. todo: check for the correct sensor id

Closing the Sensor Connection

Once you are done with sampling sensor values, you can release the connection to the
sensor and close the connection with the client:

sensor.release();
client.close();