[ros-users] camera_info message and stereo_image_proc

[Rosen Diankov]

hi kurt,

When D and K are optimized for in camera calibration, K is always
performed after undistortion, therefore K always points to the
undistorted image.

The  "internal camera matrix describing the focal length and center of
the original (distorted) image" should always be equivalent to the
intrinsic matrix of the "undistorted, rectified image". P is usually
used to change coordinate systems of the image to make other math
simpler, one example being rectification.

Regardless, given P, we can usually separate it into K*T where T is an
affine matrix. And this K should always be equivalent to the intrinsic
image of the camera unless the image is cropped or scaled (ie the ROI
you describe in the wiki). Does any other transformation happen inside
the stereo frame that explains why one CameraInfo message holds two
sets of parameters?

thank you,
rosen,

2010/4/14 Kurt Konolige <konolige at willowgarage.com>:
> Rosen, Dejan -
>
> Please see the sensor_msgs/CameraInfo.msg header file
> (http://www.ros.org/doc/api/sensor_msgs/html/msg/CameraInfo.html), and
> the description of the calibration process in OpenCV.  It would help
> also, I think, if there were explicit information in the wiki
> tutorials on the meaning of the CameraInfo parameters - we'll put this
> in.  But the main idea is in the comments in the CameraInfo header
> file.
>
> There are two sets of parameters.  One deals with the original,
> distorted image.  These are D,K,R.  D, the distortion parameters,
> describe the lens distortion.  K is the internal camera matrix, and
> describes the focal length and center of the original (distorted)
> image.  R is a rectification matrix for warping the image into a
> "normal form" for stereo, if desired; if no rectification is done
> (e.g., for monocular cameras), it is the identity matrix.
>
> The other parameter is the projection matrix P.  This matrix refers to
> the undistorted, rectified image.  It gives the transform from XYZ
> world points in the camera frame, to image points.  Note that it is
> really the multiplication of the projection matrix for normalized
> (focal length = 1) images, and the internal parameters of the
> undistorted, rectified image:  P (CameraInfo) = K'P', where P' is the
> standard projection matrix dealing with normalized images, and K' is
> the undistorted, rectified image internal parameter matrix.
>
> Hope this helps...
>
> Kurt
>
>
>
> On Tue, Apr 13, 2010 at 9:27 AM, Rosen Diankov <rosen.diankov at gmail.com> wrote:
>> Hi Blaise, Dejan,
>>
>> thank you for the responses.
>>
>> We have several ros nodes that compute the 6D pose of objects from
>> images. This data can come from stereo cameras, or can compute from
>> single cameras. Either way, the CameraInfo message explains how the
>> image was generated and it provides an intrinsic matrix, so we try to
>> be consistent and do all processing depending on what the CameraInfo
>> dictates.
>>
>> I don't understand how nodes can just use rectified images without
>> knowing the intrinsic parameters... is there a tf frame that does the
>> intrinsic parameter computation?
>>
>> rosen,
>>
>> 2010/4/14 Blaise Gassend <blaise at willowgarage.com>:
>>> Hi Rosen,
>>>
>>> I believe that the intent is that only image_proc and stereo_image_proc
>>> are supposed to look at CameraInfo.D. All other nodes should be running
>>> on rectified images and should disregard the distortion parameters.
>>>
>>> Do you have a use case of a node that needs to be able to run both on
>>> rectified and unrectified images and, that needs to use the distortion
>>> parameters?
>>>
>>> Blaise
>>>
>>> On Tue, 2010-04-13 at 17:42 +0900, Rosen Diankov wrote:
>>>> hi guys,
>>>>
>>>> currently i'm using the videre_stereo_cam package by Antons to get
>>>> stereo data. This publishes the image_raw and camera_info messages as
>>>> expected, which is then fed into stereo_image_proc.
>>>>
>>>> stereo_image_proc itself publishes image_rect, image_color,
>>>> image_mono, which I'm guessing undistort the raw images. However, a
>>>> new camera_info isn't published that has CameraInfo.D set to all
>>>> zeros. This confuses other nodes taking in the processed images and
>>>> the camera_info, so is it possible to publish a new camera_info
>>>> message to use for the output images?
>>>>
>>>> rosen,
>>>> _______________________________________________
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>>>
>>>
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