get the raw kinect data

Question

In openni, I think sensor_msgs encode data.

Because, rostopic echo /camera/depth/image and /camera/depth/disparity pulish not 16bit or 11bit, just 0~255.

I think the data is not actual depth data( distance )

I want to know depth value. But I don't know how to get the depth value.

I know the relation ( Z=fT/d ).

I think the fomula substituted raw data is right.

How can I get the raw kinect sensor data?

Or How can I get the actual depth value?

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Originally posted by ha on ROS Answers with karma: 1 on 2012-08-28

Post score: 0

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Original comments

Comment by ha on 2012-08-29:
I think sensor_msgs/image message format is 8bit and using cv_bridge is 16bit or 32bit. Dose from 8bit to 32bit make loss accuracy?

Answer 1

Looking at the openni_camera documentation on the ROS wiki, you can see that the openni_node broadcasts several topics.

I think for the data that you are looking for, the topics of interest will be the depth/image_raw messages, or the depth_registered/image_raw if you have the OpenNI registration turned on.

The */image_raw messages are in the sensor_msgs/Image message format, which stores the data in a byte array, that can then be reassembled in the subscriber. This is accomplished using cv_bridge.

cv_bridge allows you to write code like this for your callback:

void imageCb(const sensor_msgs::ImageConstPtr& msg)
{
  cv_bridge::CvImagePtr cv_ptr;
  try
  {
    cv_ptr = cv_bridge::toCvCopy(msg, enc::TYPE_32FC1);
  }
  catch (cv_bridge::Exception& e)
  {
    ROS_ERROR("cv_bridge exception: %s", e.what());
    return;
  }
  cv::imshow(WINDOW, cv_ptr->image);
  image_pub_.publish(cv_ptr->toImageMsg());
}

cv_ptr->image will contain an OpenCV cv::Mat, in this case containing floating point values, which represent the depth in millimeters for that pixel.

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Originally posted by mjcarroll with karma: 6414 on 2012-08-29

This answer was ACCEPTED on the original site

Post score: 2

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Original comments

Comment by shinnqy on 2014-05-21:
Can you tell how to access the floating point values in cv_ptr->image?