Calibrate a Stereo Camera

墨蓝 2022-05-28 13:48 2113阅读 0赞

*  [camera\_calibration][camera_calibration]
 *  [Tutorials][]
 *  [StereoCalibration][]

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 *  [ROS/Tutorials][ROS_Tutorials]
 *  [RecentChanges][]
 *  [StereoCalibration][StereoCalibration 1]

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<table> 
 <tbody> 
  <tr> 
   <td style="background-color:#cce0ff;"><strong>Note:</strong> This tutorial assumes that you have completed the previous tutorials: <a href="http://wiki.ros.org/ROS/Tutorials" rel="nofollow">ROS Tutorials</a>.</td> 
  </tr> 
 </tbody> 
</table>

<table> 
 <tbody> 
  <tr> 
   <td style="background-color:#bbceee;"><img alt="(!)" src="http://wiki.ros.org/moin_static197/rostheme/img/idea.png" title="(!)" width="15" height="15"> Please ask about problems and questions regarding this tutorial on <a href="http://answers.ros.org" rel="nofollow">answers.ros.org</a>. Don't forget to include in your question the link to this page, the versions of your OS &amp; ROS, and also add appropriate tags.</td> 
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</table>

# How to Calibrate a Stereo Camera #

**Description:** This tutorial cover using the [camera\_calibration][camera_calibration]'s cameracalibrator.py node to calibrate a stereo camera with a left and right image over ROS.  
  
   **Keywords:** stereo, camera, calibration  
  
   **Tutorial Level:** BEGINNER

Contents

1.  [Before Starting][]
2.  [Compiling][]
3.  [Camera Publishing][]
4.  [Start the Calibration][]
    
    1.  [Dual Checkerboards][]
5.  [Holding the Checkerboard][]
6.  [Moving the Checkerboard][]
7.  [Calibration Results][]

## Before Starting ##

Make sure that you have the following:

*  a large [checkerboard (8x6)][checkerboard _8x6] or [checkerboard (7x6)][checkerboard _7x6] with known dimensions. This tutorial uses a 8x6 checkerboard with 108mm squares 
 *  a well lit 5m x 5m area clear of obstructions and check board patterns 
 *  a stereo camera publishing left and right images over ROS (if you want to use two independent cameras as a stereo camera, you must make sure the images have identical time stamps)

**NOTE**: Checkerboard size refers to the number of internal corner, as described in the OpenCV documentation (i.e. the 8x6 checkerboard contains 9x7 squares)

## Compiling ##

Start by getting the dependencies and compiling the driver.

$ rosdep install camera_calibration
    $ rosmake camera_calibration

## Camera Publishing ##

Make sure that your stereo camera is publishing left and right images over ROS. Let's list the topics to check that the images are published:

$ rostopic list

This will show you all the topics published, check to see that there is a left and right image\_raw topic:

*      /my_stereo/left/camera_info
        /my_stereo/left/image_raw
        /my_stereo/right/camera_info
        /my_stereo/right/image_raw
        /my_stereo_both/parameter_descriptions
        /my_stereo_both/parameter_updates
        /my_stereo_l/parameter_descriptions
        /my_stereo_l/parameter_updates
        /my_stereo_r/parameter_descriptions

## Start the Calibration ##

To start the calibration you will need to load the image topics that will be calibrated:

$ rosrun camera_calibration cameracalibrator.py --size 8x6 --square 0.108 right:=/my_stereo/right/image_raw left:=/my_stereo/left/image_raw right_camera:=/my_stereo/right left_camera:=/my_stereo/left

This will open up the calibration window which will highlight the checkerboard, you will not see any images in the calibration window until a checkerboard is present:

*  ![stereo\_0.png][stereo_0.png]

### Dual Checkerboards ###

**New in D**

Starting in Diamondback, you will be able to use multiple size checkerboards to calibrate a camera.

To use multiple checkerboards, give multiple \--size and \--square options for additional boards. Make sure the boards have different dimensions, so the calibration system can tell them apart.

## Holding the Checkerboard ##

Make sure that you hold the checkerboard horizontally (more checkers horizontally than vertically).

*  ![check-108.png][]

## Moving the Checkerboard ##

In order to get a good calibration you will need to move the checkerboard around in the camera frame such that:

*  the checkerboard is detected at the left and right edges of the field of view (X calibration) 
 *  the checkerboard is detected at the top and bottom edges of the field of view (Y calibration) 
 *  the checkerboard is detected at various angles to the camera ("Skew") 
 *  the checkerboard fills the entire field of view (Size calibration) 
 *  checkerboard tilted to the left, right, top and bottom (X,Y, and Size calibration)

As you move the checkerboard around you will see three bars on the calibration sidebar increase in length. When the **CALIBRATE** button lights, you have enough data for calibration and can click **CALIBRATE** to see the results.

*  ![stereo\_1.png][stereo_1.png]

## Calibration Results ##

After the calibration is complete you will see the calibration results in the terminal and the calibrated image in the calibration window:

*  ![stereo\_2.png][stereo_2.png]

The sidebar will show the measured accuracy and dimensions of the checkerboard square, in the above case the checkerboard square was 111mm with an accuracy of 0.31 pixels.

A successful calibration will result in real-world straight edges appearing straight in the corrected image.

A failed calibration usually results in blank or unrecognizable images, or images that do not preserve straight edges.

Typically, an epipolar error below 0.25 pixel is considered acceptable, and below 0.1 excellent.

You can also use the slider at the top of the calibration window to change the size of the rectified image, as shown below. A scale of 0.0 means that the image is sized so that all pixels in the rectified image are valid. The rectified image has no border, but some pixels from the original image are discarded. A scale of 1.0 means that all pixels in the original image are visible, but the rectified image has black borders where there are no input pixels in the original image.

**The recommended value for the slider is 0.0.**

*  ![stereo\_3.png][stereo_3.png]![stereo\_4.png][stereo_4.png]

For more details on the stereo camera model - including interpretation of these results - see [http://opencv.willowgarage.com/documentation/python/camera\_calibration\_and\_3d\_reconstruction.html][http_opencv.willowgarage.com_documentation_python_camera_calibration_and_3d_reconstruction.html] and [image\_geometry][image_geometry].

Left:
    D =  [-0.31420196940339423, 0.091934927292188981, 0.0012952332628749881, -0.0016196264582460102]
    K =  [425.19601412158482, 0.0, 308.29689772295882, 0.0, 426.02702697756899, 223.53789948448997, 0.0, 0.0, 1.0]
    R =  [0.99783514664821127, 0.013543024537547797, 0.064355315242164368, -0.013644479706482148, 0.99990626305523833, 0.0011372231303031885, -0.064333881330776027, -0.0020128560018237928, 0.99792640015365552]
    P =  [308.02438413775218, 0.0, 270.8484992980957, 0.0, 0.0, 308.02438413775218, 226.91282844543457, 0.0, 0.0, 0.0, 1.0, 0.0]
    
    Right:
    D =  [-0.30550530964404188, 0.082701072309439266, 0.001966752019596593, -0.0016409796174513081]
    K =  [425.18741896821433, 0.0, 323.8787136811938, 0.0, 426.46867413824884, 226.19589833365407, 0.0, 0.0, 1.0]
    R =  [0.99769116642055589, 0.011418153515469445, 0.066947458627553177, -0.011312576360776634, 0.99993409783500409, -0.0019559148698406695, -0.066965379581335679, 0.0011940507500265176, 0.99775458514623427]
    P =  [308.02438413775218, 0.0, 270.8484992980957, -28.144333365644293, 0.0, 308.02438413775218, 226.91282844543457, 0.0, 0.0, 0.0, 1.0, 0.0]
    # oST version 5.0 parameters
    
    
    [image]
    
    width
    640
    
    height
    480
    
    [narrow_stereo/left]
    
    camera matrix
    425.196014 0.000000 308.296898
    0.000000 426.027027 223.537899
    0.000000 0.000000 1.000000
    
    distortion
    -0.314202 0.091935 0.001295 -0.001620 0.0000
    
    rectification
    0.997835 0.013543 0.064355
    -0.013644 0.999906 0.001137
    -0.064334 -0.002013 0.997926
    
    projection
    308.024384 0.000000 270.848499 0.000000
    0.000000 308.024384 226.912828 0.000000
    0.000000 0.000000 1.000000 0.000000
    
    
    # oST version 5.0 parameters
    
    
    [image]
    
    width
    640
    
    height
    480
    
    [narrow_stereo/right]
    
    camera matrix
    425.187419 0.000000 323.878714
    0.000000 426.468674 226.195898
    0.000000 0.000000 1.000000
    
    distortion
    -0.305505 0.082701 0.001967 -0.001641 0.0000
    
    rectification
    0.997691 0.011418 0.066947
    -0.011313 0.999934 -0.001956
    -0.066965 0.001194 0.997755
    
    projection
    308.024384 0.000000 270.848499 -28.144333
    0.000000 308.024384 226.912828 0.000000
    0.000000 0.000000 1.000000 0.000000

If you are satisfied with the calibration, click **COMMIT** (on the pictures above this is button has an old name **UPLOAD**) to send the calibration parameters to the camera for permanent storage.

If you want to save the calibration parameters and images used in calibration, click **SAVE**. Everything will be made available in the compressed folder /tmp/calibrationdata.tar.gz.

Wiki: camera\_calibration/Tutorials/StereoCalibration (last edited 2017-04-20 17:48:21 by [AdamAllevato][])

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[camera_calibration]: http://wiki.ros.org/camera_calibration
[Tutorials]: http://wiki.ros.org/camera_calibration/Tutorials
[StereoCalibration]: http://wiki.ros.org/action/fullsearch/camera_calibration/Tutorials/StereoCalibration?action=fullsearch&context=180&value=linkto%3A%22camera_calibration%2FTutorials%2FStereoCalibration%22
[Distributions]: http://wiki.ros.org/Distributions
[ROS_Installation]: http://wiki.ros.org/ROS/Installation
[ROS_Tutorials]: http://wiki.ros.org/ROS/Tutorials
[RecentChanges]: http://wiki.ros.org/RecentChanges
[StereoCalibration 1]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration
[Info]: http://wiki.ros.org/action/info/camera_calibration/Tutorials/StereoCalibration?action=info
[Attachments]: http://wiki.ros.org/action/AttachFile/camera_calibration/Tutorials/StereoCalibration?action=AttachFile
[Login]: http://wiki.ros.org/action/login/camera_calibration/Tutorials/StereoCalibration?action=login
[Before Starting]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Before_Starting
[Compiling]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Compiling
[Camera Publishing]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Camera_Publishing
[Start the Calibration]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Start_the_Calibration
[Dual Checkerboards]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Dual_Checkerboards
[Holding the Checkerboard]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Holding_the_Checkerboard
[Moving the Checkerboard]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Moving_the_Checkerboard
[Calibration Results]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration#Calibration_Results
[checkerboard _8x6]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration?action=AttachFile&do=view&target=check-108.pdf
[checkerboard _7x6]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration?action=AttachFile&do=view&target=check_7x6_108mm.pdf
[stereo_0.png]: /images/20220528/b7cf49f1eda94ba5829ef3f0c0bbfbe3.png
[check-108.png]: /images/20220528/a54060945cee426b8322d05ae5c674ef.png
[stereo_1.png]: /images/20220528/338a3fc17afe485388628d59bf9413ca.png
[stereo_2.png]: /images/20220528/7e726ea7a7a540978c7cbbc7efe4d133.png
[stereo_3.png]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration?action=AttachFile&do=get&target=stereo_3.png
[stereo_4.png]: http://wiki.ros.org/camera_calibration/Tutorials/StereoCalibration?action=AttachFile&do=get&target=stereo_4.png
[http_opencv.willowgarage.com_documentation_python_camera_calibration_and_3d_reconstruction.html]: http://opencv.willowgarage.com/documentation/python/camera_calibration_and_3d_reconstruction.html
[image_geometry]: http://wiki.ros.org/image_geometry
[AdamAllevato]: http://wiki.ros.org/AdamAllevato
[Creative Commons Attribution 3.0]: http://creativecommons.org/licenses/by/3.0/
[Find us on Google]: https://plus.google.com/113789706402978299308
[brought_by_horiz.png]: /images/20220528/7d50bc06e7fd440ea15e680dac5150f1.png
[brought_by_horiz.png 1]: http://www.osrfoundation.org