## repository: https://code.ros.org/svn/ros-pkg
<<PackageHeader(polled_camera)>>
<<TOC(4)>>

== Overview ==
`polled_camera` defines the ROS interface that client nodes use to request images from a polling camera driver node (e.g. [[prosilica_camera]]). The protocol is:
 * The camera driver advertises a service call `<camera>/request_image` of type <<SrvLink(polled_camera/GetPolledImage)>>.
 * The client calls the service, specifying an output namespace.
 * On receiving a request, the driver captures an image and returns its time stamp in the service response.
 * The driver publishes (latching) the <<MsgLink(sensor_msgs/Image)>> and <<MsgLink(sensor_msgs/CameraInfo)>> to `<response_namespace>/image_raw` and `<response_namespace>/camera_info`.
 * Clients subscribe to the response topics just like any other camera image stream.
 * When a disconnection causes the number of subscribers to drop to zero, the publisher shuts down.

See the [[http://www.ros.org/doc/api/polled_camera/html/|code API]] (unstable) for more information on writing polled camera drivers or clients.

There are several reasons for publishing images to topics instead of returning them from the service call:
 * Consistency. Client-side processing is always performed in an image callback, regardless of what type of camera is used.
 * Visibility. Topics can be monitored in [[image_view]] or [[rviz]].
 * Reproducibility. Topics can be [[rosbag|bagged]] and played back later.
 * Compression: Can take advantage of [[image_transport]] to compressed images, if desired.

== Nodes ==
=== poller ===
Continually requests images from a polled camera at a specified rate in Hz, making the camera look like it is capturing continuously.

Usage:
{{{
# Poll "my_camera" at 5 Hz, publishing in namespace my_polled_output/.
$ poller 5 camera:=my_camera output:=my_polled_output
}}}
{{{
#!clearsilver CS/NodeAPI
pub {
  0.name = <output>/image_raw
  0.type = sensor_msgs/Image
  0.desc = Image topic, actually published by the camera driver. `output` should be remapped by the user.
  1.name = <output>/camera_info
  1.type = sensor_msgs/CameraInfo
  1.desc = Info topic, actually published by the camera driver. `output` should be remapped by the user.
}
srv_called {
  0.name = <camera>/request_image
  0.type = polled_camera/GetPolledImage
  0.desc = The camera driver's polled image service. `camera` should be remapped by the user to the camera namespace.
}
}}}


## AUTOGENERATED DON'T DELETE
## CategoryPackage