Hi Homer,

DisparityImage stores the disparity data as a binary blob (uint8[] data),
but the disparities are floats. If you're using OpenCV, you can get a nice
view of the data like this:

const cv::Mat_<float> dmat(disparity_msg->image.height,
                           disparity_msg->image.width,
                           (float*)&disparity_msg->image.data[0],
                           disparity_msg->image.step);

Then do dmat(x,y) as Daniel said.

Cheers,
Patrick

On Wed, Feb 2, 2011 at 7:14 PM, Daniel Maturana <dimatura@gmail.com> wrote:

> It is in the image itself, that is the disparity at position x,y is at
> image(x,y). You could also use the Z value of the points in the point
> cloud.
> Daniel
>
> On Wed, Feb 2, 2011 at 8:28 PM, Homer Manalo
> <homer.manalo@roboteknik.com> wrote:
> > Anyone knows how to get d(disparity) from the DisparityImage.msg?
> >
> > On Wed, Feb 2, 2011 at 5:33 PM, Homer Manalo <
> homer.manalo@roboteknik.com>
> > wrote:
> >>
> >> According to the documentation of DisparityImage.msg:
> >>
> >> http://www.ros.org/doc/api/stereo_msgs/html/msg/DisparityImage.html
> >>
> >> depth can be calculated by Z=fT/d, so far I can get the minimum
> distance:
> >>
> >>         distance = data.f*data.T/data.max_disparity
> >>     print "Minimum distance:", distance, "meters"
> >>
> >>         Minimum distance: 0.430558934726 meters
> >>
> >> How do you get d(disparity) here?
> >>
> >> On Wed, Feb 2, 2011 at 11:37 AM, Homer Manalo
> >> <homer.manalo@roboteknik.com> wrote:
> >>>
> >>> Ok, so I need to manually extract this? Or is there a command to show
> >>> this up? Which one is it contained:
> >>>
> >>> [sensor_msgs/PointCloud2]:
> >>> Header header
> >>>   uint32 seq
> >>>   time stamp
> >>>   string frame_id
> >>> uint32 height
> >>> uint32 width
> >>> sensor_msgs/PointField[] fields
> >>>   uint8 INT8=1
> >>>   uint8 UINT8=2
> >>>   uint8 INT16=3
> >>>   uint8 UINT16=4
> >>>   uint8 INT32=5
> >>>   uint8 UINT32=6
> >>>   uint8 FLOAT32=7
> >>>   uint8 FLOAT64=8
> >>>   string name
> >>>   uint32 offset
> >>>   uint8 datatype
> >>>   uint32 count
> >>> bool is_bigendian
> >>> uint32 point_step
> >>> uint32 row_step
> >>> uint8[] data
> >>> bool is_dense
> >>>
> >>> [stereo_msgs/DisparityImage]:
> >>> Header header
> >>>   uint32 seq
> >>>   time stamp
> >>>   string frame_id
> >>> sensor_msgs/Image image
> >>>   Header header
> >>>     uint32 seq
> >>>     time stamp
> >>>     string frame_id
> >>>   uint32 height
> >>>   uint32 width
> >>>   string encoding
> >>>   uint8 is_bigendian
> >>>   uint32 step
> >>>   uint8[] data
> >>> float32 f
> >>> float32 T
> >>> sensor_msgs/RegionOfInterest valid_window
> >>>   uint32 x_offset
> >>>   uint32 y_offset
> >>>   uint32 height
> >>>   uint32 width
> >>> float32 min_disparity
> >>> float32 max_disparity
> >>> float32 delta_d
> >>>
> >>>
> >>> Thanks,
> >>> Homer
> >>>
> >>> On Wed, Feb 2, 2011 at 11:17 AM, Daniel Maturana <dimatura@gmail.com>
> >>> wrote:
> >>>>
> >>>> Both the the disparity and the points2 messages have the information
> >>>> you need. Note that your camera should be calibrated.
> >>>> best,
> >>>> Daniel
> >>>>
> >>>> On Tue, Feb 1, 2011 at 8:13 PM, Homer Manalo
> >>>> <homer.manalo@roboteknik.com> wrote:
> >>>> > I've actually used it for viewing disparity and rectifying images.
> >>>> > What
> >>>> > topic exactly are you referring to?
> >>>> >
> >>>> > Homer
> >>>> >
> >>>> > On Tue, Feb 1, 2011 at 11:43 PM, Daniel Maturana <
> dimatura@gmail.com>
> >>>> > wrote:
> >>>> >>
> >>>> >> Try http://www.ros.org/wiki/stereo_image_proc.
> >>>> >> Daniel
> >>>> >>
> >>>> >> On Tue, Feb 1, 2011 at 4:13 AM, Homer Manalo
> >>>> >> <homer.manalo@roboteknik.com> wrote:
> >>>> >> > Are there packages that convert stereo data into real world
> >>>> >> > measurements
> >>>> >> > -
> >>>> >> > how far an object is from camera?
> >>>> >> >
> >>>> >> > Thanks,
> >>>> >> > Homer
> >>>> >> >
> >>>> >> > _______________________________________________
> >>>> >> > ros-users mailing list
> >>>> >> > ros-users@code.ros.org
> >>>> >> > https://code.ros.org/mailman/listinfo/ros-users
> >>>> >> >
> >>>> >> >
> >>>> >> _______________________________________________
> >>>> >> ros-users mailing list
> >>>> >> ros-users@code.ros.org
> >>>> >> https://code.ros.org/mailman/listinfo/ros-users
> >>>> >
> >>>> >
> >>>
> >>
> >
> >
> > _______________________________________________
> > ros-users mailing list
> > ros-users@code.ros.org
> > https://code.ros.org/mailman/listinfo/ros-users
> >
> >
> _______________________________________________
> ros-users mailing list
> ros-users@code.ros.org
> https://code.ros.org/mailman/listinfo/ros-users
>