D435 get_distance and dept frame pixel value *depth_scale isn't same

[asbilgi]

Required Info
Camera Model	{ D415, D435 }
Firmware Version	(5.12.6)
Operating System & Version	{Linux (Ubuntu 16)
Kernel Version (Linux Only)	(e.g. 4.15.0)
Platform	PC / nano Pi M4
SDK Version	{2.34.1}
Language	{C++ }

Issue Description

I want to obtain the depth of some point in depth frame. But get_distance() and pixel value *get_depth_scale isn't same. Here is sample code:

` int main(){

rs2::config m_config;

m_config.enable_stream(RS2_STREAM_DEPTH, 1280, 720, rs2_format::RS2_FORMAT_Z16, 15);

rs2::pipeline m_pipeline;

rs2::pipeline_profile m_pipelineProfile = m_pipeline.start(m_config);

std::vector<rs2::sensor> m_sensorList = m_pipelineProfile.get_device().query_sensors();

while(true){

    rs2::frameset frameset = m_pipeline.wait_for_frames();

    rs2::video_frame tIRFrameL = frameset.get_infrared_frame(1);

    rs2::depth_frame tDepthFrame = frameset.get_depth_frame();

    cv::Mat tImageDepth1DTest;

    tImageDepth1DTest = cv::Mat( cv::Size(1280, 720), CV_16U, (uchar *)( tDepthFrame.get_data()), cv::Mat::AUTO_STEP);

    int testtt = tImageDepth1DTest.at<uchar>(500, 500);

    float tscale = 0.;

    for(auto tSensor : m_sensorList){

        std::string tSensorName(tSensor.get_info(RS2_CAMERA_INFO_NAME));

        if( tSensorName == "Stereo Module"){

            tscale = tSensor.as<rs2::depth_sensor>().get_depth_scale();

        }

    }

    std::cout << "Scale: " << tscale << " Pixel value: " << testtt << " distance: " << tDepthFrame.get_distance(500, 500) <<std::endl;

}}`

and result here:
Scale: 0.001 Pixel value: 246 distance: 3.549
Scale: 0.001 Pixel value: 234 distance: 3.513
Scale: 0.001 Pixel value: 234 distance: 3.489
Scale: 0.001 Pixel value: 40 distance: 3.549
Scale: 0.001 Pixel value: 234 distance: 3.525
Scale: 0.001 Pixel value: 66 distance: 3.562
Scale: 0.001 Pixel value: 185 distance: 3.574

[MartyG-RealSense]

Hi @asbilgi I hope that the discussion in the link below will be helpful to you.

#7264

[asbilgi]

Hi @MartyG-RealSense link very helpful to me.
To obtain depth value you should convert CV_64F also in opencv.
And found cv_helper.hpp it's include opencv conversation.
https://github.com/IntelRealSense/librealsense/blob/025fccf76803ee6a6e60de9f18ac6193b7ff8597/wrappers/opencv/cv-helpers.hpp

[sandeshk1]

Could someone explain how the two values were fixed and same

[MartyG-RealSense]

Hi @sandeshk1 I think you are asking how @asbilgi achieved getting the same distance values from both get_distance and by the alternate method of multiplying the pixel value by the depth unit scale?

Edit: I see that you have been replied to about this question at your own case at #8150

[sandeshk1]

@MartyG-RealSense Thats right.. Thanks