Depth output values

I am trying to work to get the depth of the center pixel using the sample tutorial that’s provided by the ZED. I have a doubt about the depth values I am getting as output

    void depthCallback(const sensor_msgs::msg::Image::SharedPtr msg) {
        // Get a pointer to the depth values casting the data
        // pointer to floating point
        float* depths = (float*)(&msg->data[0]);

        // Image coordinates of the center pixel
        int u = msg->width / 2;
        int v = msg->height / 2;

        // Linear index of the center pixel
        int centerIdx = u + msg->width * v;

        // Output the measure
        RCLCPP_INFO(get_logger(), "Center distance : %g m", depths[centerIdx]);

Above is the code that takes the center pixel and outputs as depth but when I try to echo the depth topic I only see the values from 0-255 which are grayscale values.

I am not understanding how did they convert those values to depth or distance in m.
Thanks in advance for your help.

The rostopic echo command displays the “data” value of the depth map topic as 8bit unsigned char, not as floating-point values.

Indeed the depthCallback in the example performs a cast conversion:
float* depths = (float*)(&msg->data[0]);