Access and Set Device Info

In this tutorial, we learn how to set device information with Aravis API.

Prerequisite

• Aravis (included in SDK package)
• GObject (included in SDK package)

Tutorial

We learned how to get device information with Aravis API in the previous tutorial.

Some of GenICam features, such as Gain and ExposureTime is writable, so let's change these values to control Camera.

Load required modules

The process of including aravis header is exactly the same as in the last tutorial. See the detail in Access and Display Device Info.

Access to devices

The API of acess to devices is exactly the same as in the last tutorial. See the detail in Access and Display Device Info.

Get current values of the device

First of all, we want to know the current values of Gain and ExposureTime. As we learned in the previous tutorial, use arv_device_get_float_feature_value to obtain camera information after opening a camera.

for (unsigned int i = 0; i < n_devices; ++i){
    const char* dev_id = arv_get_device_id (i);
    ArvDevice* device = arv_open_device(dev_id, nullptr);

    double current_gain = arv_device_get_float_feature_value(device, "Gain", &error);
    if (error){
        throw std::runtime_error(error->message);
    }
    printf("%20s : %lf\n", "Gain", current_gain);
    
    double current_exposuretime = arv_device_get_float_feature_value(device, "ExposureTime", &error);
    if (error){
        throw std::runtime_error(error->message);
    }
    printf("%20s : %lf\n", "ExposureTime", current_exposuretime);
    ...
    g_object_unref (device);
}

Some examples of general keys defined in U3V devices are listed in the table below.

Feature Name	Description	Type
Gain	Gain of the image sensor	Double
ExposureTime	Exposure time of the image sensor	Double

tip

Those feature keys and types are defined in SFNC (Standard Features Naming Convention) by emva; however, some of the devices have their own unique features, keys or types. To know the all accessible features, use arv-tool-0.8. See the detail in List the available GenICam features.

Common names (example):

• Instead of Gain, it may be GainRaw or GainAbs.
• Instead of ExposureTime, it may be ExposureTimeBaseAbs or ExposureTimeRaw.

Common types (example):

• Instead of arv_device_get_float_feature_value, it may be arv_device_get_integer_feature_value if the type of Gain or ExposureTime is Integer.

why it does not work

If arv-device-error-quark returns errors:

• The device may not have the key (Not found (1)): check if the feature key is correct. See the details in List the available GenICam features.
• The type was wrong (Not a ArvGcString (0) or Not a ArvGcFlaot (0)) check if the feature type is correct. See the details in List the available GenICam features.

Set current values of the device

Now, let's update the Gain and ExposureTime value with API of arv_device_set_float_feature_value as follows:

double new_gain = current_gain + 10.0;
arv_device_set_float_feature_value(device, "Gain", new_gain, &error);
if (error){
    throw std::runtime_error(error->message);
}

double new_exposuretime = current_exposuretime + 20.0;
arv_device_set_float_feature_value(device, "ExposureTime", new_exposuretime, &error);
if (error){
    throw std::runtime_error(error->message);
}

To confirm if the values are actually updated, you can load the device info again.

current_gain = arv_device_get_float_feature_value(device, "Gain", &error);
if (error){
    throw std::runtime_error(error->message);
}
printf("%20s : %lf\n", "Gain", current_gain);

current_exposuretime = arv_device_get_float_feature_value(device, "ExposureTime", &error);
if (error){
    throw std::runtime_error(error->message);
}
printf("%20s : %lf\n", "ExposureTime", current_exposuretime);

Close

Using the following function in Aravis can release resources that avoid memory leaks.

g_object_unref (device);

tip

Instead of using Aravis Python API, you can also use arv-tool. See the detail in Tools from Aravis

Complete code

Complete code used in the tutorial is here.