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 <
advait@cc.gatech.edu> 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 <tfoote@willowgarage.com>
> 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 <advait@cc.gatech.edu>
> 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
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
TullyOn Tue, Jun 8, 2010 at 7:13 AM, Advait Jain <
advait@cc.gatech.edu> 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 <
tfoote@willowgarage.com> 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 <
advait@cc.gatech.edu> 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 FooteSystems EngineerWillow Garage, Inc.
tfoote@willowgarage.com(650) 475-2827
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