Hi Dejan,

Assuming that you're running with a fairly standard PR2 configuration, the laser controller that you're running is documented here:
http://www.ros.org/wiki/pr2_mechanism_controllers/LaserScannerTrajController

The set_periodic_cmd service call can execute only a subset of the profiles that are possible with set_traj_cmd.  set_periodic_cmd can only do triangle wave profiles where the laser moves the same speed on both the up and down sweep.

The set_traj_cmd lets you specify all the timepoints of the trajectory, giving much more flexibility.

Suppose you have a periodic command with period=4, amplitude=2, and offset=1.  The equivalent trajectory command would have the following timepoints:
time_from_start=0, pos=3
time_from_start=2, pos=-1
time_from_start=4, pos=3

Hopefully this helps!
Vijay

On Sat, Sep 11, 2010 at 3:31 PM, Dejan Pangercic <dejan.pangercic@gmail.com> wrote:
Hi there,
I noticed that there are 2 ways to configure laser_tilt_controller,
one with pr2_msgs/LaserTrajCmd (as in e.g. pr2_move_base,
pr2_move_base.py) message and
second with a pr2_msgs/PeriodicCmd (as in e.g. send_periodic_cmd.py).
What is the actual difference? Can one somehow find the mapping
between
their values?

I have a case where I drive(using pr2_2dnav) around with the PR2, halt
at the certain locations and map the environment. The tilting rate at
mapping has to of course be significantly  slower that the one needed
by the "pr2_2dnav" application which requires constant back-and-forth
reconfiguration. So far my preferred method of configuring the
laser_tilt_controller was by using the send_periodic_cmd.py program
but then I do not seem to be able to hit the same configuration as
done by the  "pr2_2dnav" which consequentially results in sloppy
performance by the latter.
So if the mapping between both messages is possible I'd be
tremendously glad to learn about.

thx and cheers, D.

--
MSc. Dejan Pangercic
PhD Student/Researcher
Intelligent Autonomous Systems Group
Technische Universität München
Telephone: +49 (89) 289-26908
E-Mail: dejan.pangercic@cs.tum.edu
WWW: http://ias.cs.tum.edu/people/pangercic
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--
Vijay Pradeep
Systems Engineer
Willow Garage, Inc.
vpradeep@willowgarage.com