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