What is the best way to get depth values from kinect?

Question

I have installed ros with the kinect drivers in ubuntu and have it all up and running.i'm new to ros.

What I am ultimately trying to achieve is this: extract the distance in millimetres of a particular point in an RGB image. So what ever the kinect sees in front of it I want to be able to get the depth values out of it. i'm not sure which topic I need to use and

I had a look at:

depth/image_raw (sensor_msgs/Image) Raw image from device. Contains uint16 depths in mm.

But this seems to return each pixel as a max value of 256 and not a u16bit int when viewing the topic by running rostopic echo /camera/depth/image_raw ... how do I convert this depth into millimetres? is the the best one to use at all? or should I use something else?

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Originally posted by Maltenrazer on ROS Answers with karma: 36 on 2012-04-27

Post score: 0

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Original comments

Comment by kshitij on 2012-04-30:
If you want to extract depth values from an RGB image, you'd probably want to use a registered depth image, i.e. one in which the Depth values are aligned with RGB values. So try using: camera/depth_registered/image

Answer 1

Take a look at depth_image_proc and openni_launch. Also do a search here on answers.ros.org for kinect. Between these three things, it should give you a good head start ... good luck!

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Originally posted by Kevin with karma: 2962 on 2012-04-27

This answer was ACCEPTED on the original site

Post score: 1

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Original comments

Comment by fairy on 2013-07-25:
the depth values that obtain by kinect driver is actually a no. of streams that continuously changing even if kinect remain stationary can u tell me plz y is it so?

secondly if i want to access the depth of particular point out of the depth of all points that is seen by kinect, how can i do it? plz guide me

Comment by askkvn on 2021-06-25:
@fairy check my answer below to get depth value at a specific point