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

• 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.

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 ZenSensorEvent_SensorFound:
            std::cout << "Found sensor " << event.data.sensorFound.name << std::endl;
            break;

        case ZenSensorEvent_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");
auto& obtainError = sensorPair.first;
auto& sensor = sensorPair.second;
if (obtainError)
{
    // error while obtaining the sensor
    return obtainError;
}

Please check the documentation in the section IO Systems. 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 inetrial 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 ZenImuEvent_Sample:
            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;
            std::cout << "> Gyro: \t\t x = " << event.data.imuData.g[0]
                << "\t y = " << event.data.imuData.g[1]
                << "\t z = " << event.data.imuData.g[2] << std::endl;
        break;
    }
}

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 ZenGnssEvent_Sample:
            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;
    }
}

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();