Advait, Indeed it's agreed upon, but was too close to the release of cturtle to get it implemented, reviewed, and tested before the freeze. I created a ticket to keep track of this. https://code.ros.org/trac/ros-pkg/ticket/4218 Tully On Tue, Jun 8, 2010 at 7:13 AM, Advait Jain wrote: > Hi Tully, > > The wiki link was very helpful. > > Here's my two cents: > > I believe that everything used to define a twist should be explicit in the > twist > message. As a tf user, I would prefer to provide all the information rather > than > follow certain conventions. > > From the wiki link: > "There is a consensus to collapse the reference point and reference frame > into > a single coordinate frame." > Mathematically, this seems ok to me too. However, will this involve a > significant > overhead in the implementation, such as adding new frames to the tf tree, > make > the code messy etc, if I want to find the velocity of a large number > of different > points in the frame of the gripper? > > Providing a reference point (in reference frame coordinates) does not seem > like > too much additional information to me. > > Advait > > > On Tue, Jun 8, 2010 at 1:52 AM, Tully Foote > wrote: > > Hi Advait, > > > > There has been a bit of discussion of how to deal with twists well. > However > > how to transform them has many different meanings implied by how they are > > represented. In particular we found there were 4 different conventions > > without a clear way to distinguish between them. There is the results of > an > > API review at http://www.ros.org/wiki/tf/Reviews/2010-03-12_API_Review > > > > The biggest problem is that there is a lot of semantic information > carried > > in an instance of a Twist. Without forcing a lot of conventions on users > we > > could not find a way to transform Twists without requiring a lot of extra > > information. > > > > There is an API to get the twist between two frames in the cturtle > version > > of tf. > > > > And kdl provides may twist manipulation methods which are recommended for > > computing things involving twists. > > > > If anyone else has input we can come back to this. I would like to add > this > > capability, but building a consensus on representations will be required. > > > > Tully > > > > On Mon, Jun 7, 2010 at 5:00 PM, Advait Jain > wrote: > >> > >> I just realized that the wrench and twist messages currently > >> do not explicitly store the point at which the wrench or twist > >> is expressed. > >> > >> Is there is support in TF or somewhere else for getting the > >> equivalent twist or wrench at a different point in space? > >> > >> e.g. to get the equivalent wrench at point B given a wrench > >> acting at point A, I would use: > >> Force at point A = Force at point B > >> Torque at point A = vector from A to B X Force + Torque at point B > >> > >> It would be nice to have easy ways to be able to say, for > >> example, that given a force that the robot is applying at the > >> door handle, what the torque is at the hinge of the door. > >> > >> Another example could be if the we want a robot to perform > >> a bi-manual and need to compute the motion of two points > >> on the same rigid body. > >> > >> I think it would be really cool if TF could also shift twists, > >> wrenches correctly in addition to changing coordinate frames. > >> > >> What are other people's thoughts about this? > >> > >> > >> Advait > >> _______________________________________________ > >> ros-users mailing list > >> ros-users@code.ros.org > >> https://code.ros.org/mailman/listinfo/ros-users > > > > > > > > -- > > Tully Foote > > Systems Engineer > > Willow Garage, Inc. > > tfoote@willowgarage.com > > (650) 475-2827 > > > > _______________________________________________ > > 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 > -- Tully Foote Systems Engineer Willow Garage, Inc. tfoote@willowgarage.com (650) 475-2827