Subscriber

Overview

The _subscriber node subscribes to the sensor_data topic and evaluates incoming sensor data (temperature, humidity, and pressure) using a custom ROS2 message type: custom_interfaces::msg::DataCollect. It prints a color-coded summary to the terminal, indicating whether each value is within the given range.

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The Subscriber Class

The core of this node is the Subscriber class, which inherits from rclcpp::Node. It manages the subscription and the logic for analyzing and displaying sensor data.

class Subscriber : public rclcpp::Node {
public:
    Subscriber();
    ~Subscriber() = default;
    void topic_callback(const custom_interfaces::msg::DataCollect &msg);
    std::string analyseInfo(double temp, double hum, double pression);
private:
    rclcpp::Subscription<custom_interfaces::msg::DataCollect>::SharedPtr subscription_;
};

Key Methods

• Constructor (Subscriber())
  Initializes the node and creates a subscription to the sensor_data topic using the custom message type.

• topic_callback(const custom_interfaces::msg::DataCollect &msg)
  Callback function triggered on each new message. It calls analyseInfo and logs the formatted analysis.

• analyseInfo(double temp, double hum, double pression)
  Evaluates the sensor data and returns a formatted string with color-coded results.

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How It Works

Initialization

The constructor sets up the subscription:

Subscriber::Subscriber() : Node("_subscriber")
{
    subscription_ = this->create_subscription<custom_interfaces::msg::DataCollect>(
        "sensor_data", 10, std::bind(&Subscriber::topic_callback, this, _1));
}

Message Analysis

The analyseInfo method checks each value and builds a color-coded summary:

std::string Subscriber::analyseInfo(double temp, double hum, double pression)
{
    std::string str;
    if (temp >= 15 && temp <= 30) {
        str += "\n\n\033[32m- Temperature \"" + std::to_string(temp);
        str += "\" is included between [15, 30]\033[0m\n\n";
    } else {
        str += "\n\n\033[31m- Temperature \"" + std::to_string(temp);
        str += "\" is not included between [15, 30]\033[0m\n\n";
    }
    if (hum >= 30 && hum <= 70) {
        str += "\033[32m- Humidity \"" + std::to_string(hum);
        str += "\" is included between [30, 70]\033[0m\n\n";
    } else {
        str += "\033[31m- Humidity \"" + std::to_string(hum);
        str += "\" is not included between [30, 70]\033[0m\n\n";
    }
    if (pression >= 950 && pression <= 1050) {
        str += "\033[32m- Pressure \"" + std::to_string(pression);
        str += "\" is included between [950, 1050]\033[0m\n\n";
    } else {
        str += "\033[31m- Pressure \"" + std::to_string(pression);
        str += "\" is not included between [950, 1050]\033[0m\n\n";
    }
    return str;
}

Callback Function

The callback processes each message and logs the analysis:

void Subscriber::topic_callback(const custom_interfaces::msg::DataCollect &msg)
{
    std::string str = this->analyseInfo(msg.temperature, msg.humidity, msg.pressure);
    RCLCPP_INFO(this->get_logger(), "%s", str.c_str());
}

Main Function

The main function initializes ROS2, spins the node, and shuts down cleanly:

int main(int ac, char **av)
{
    rclcpp::init(ac, av);
    rclcpp::spin(std::make_shared<Subscriber>());
    rclcpp::shutdown();
    return 0;
}

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Example

If the node receives the following message (via the custom message):

• temperature = 25
• humidity = 50
• pressure = 1000

The output will be:

• Temperature "25" is included between [15, 30]
• Humidity "50" is included between [30, 70]
• Pressure "1000" is included between [950, 1050]

Each line is color-coded in the terminal for clarity (green when no error and red when values are'nt in the correct ranges).

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