Peshala,

For question 1 you need to add a plugin description file.  See
http://www.ros.org/wiki/pluginlib  linked from here
http://www.ros.org/wiki/filters  You will both need to add this file and
export it in the manifest.

To run it inside the scan_to_scan_filter_chain node you just need to add
your filter to the nodes configuration parameters.  See 3.2.2 in
http://www.ros.org/wiki/filters#Steps_to_create_a_filter  There is specific
documentation on scan_to_scan_filter_chain node at
http://www.ros.org/wiki/laser_filters

For question 2, filters can be run in any node.  The filters::FilterChain
class is the recommended way to instantiate filters in code.  However for
your purposes the scan_to_scan_filter_chain node is likely the easiest.

Tully

On Wed, Mar 31, 2010 at 12:05 AM, Peshala Jayasekara
<peshala_24@yahoo.com>wrote:

> Dear Ros-Users,
>
> I am thinking of writing a background subtraction filter for my incoming
> laser data through hokoyo_node.
>
> Here are my problems.
>
> 1) After going through the examples of laser_filters, I thought I can use
> scan_to_scan_filter_chain node to run "background_subtraction_filter-which
> is the one I am writing, inside it. However, it gave an error msg saying
>
> According to the loaded plugin descriptions the class
> LaserBackgroundSubtractionFilter with base class type
> filters::FilterBase<sensor_msgs::LaserScan> does not exist.
>
> Is there a way to run a user's filter inside scan_to_scan_filter_chain
> node?
>
> 2) On the other hand, once you write your own filter according to the
> "Implementing a simple filter" tutorial how do you run it - what node should
> it be associated with ?
>
> Thank you in advance
> Peshala
>
>
>
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-- 
Tully Foote
Systems Engineer
Willow Garage, Inc.
tfoote@willowgarage.com
(650) 475-2827