No subject

Tue Mar 2 09:14:18 PST 2010

&quot;There is a consensus to collapse the reference point and reference fr=
ame into 
a single coordinate frame.&quot; 
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, m=
ake 
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 
<div><div></div><div class=3D"h5"> 
 
On Tue, Jun 8, 2010 at 1:52 AM, Tully Foote &lt;<a href=3D"mailto:tfoote at wi=
llowgarage.com">tfoote at willowgarage.com</a>&gt; wrote: 
&gt; Hi Advait, 
&gt; 
&gt; There has been a bit of discussion of how to deal with twists well.=A0=
 However 
&gt; how to transform them has many different meanings implied by how they =
are 
&gt; represented.=A0 In particular we found there were 4 different conventi=
ons 
&gt; without a clear way to distinguish between them.=A0 There is the resul=
ts of an 
&gt; API review at <a href=3D"http://www.ros.org/wiki/tf/Reviews/2010-03-12=
_API_Review" target=3D"_blank">http://www.ros.org/wiki/tf/Reviews/2010-03-1=
2_API_Review</a> 
&gt; 
&gt; The biggest problem is that there is a lot of semantic information car=
ried 
&gt; in an instance of a Twist.=A0 Without forcing a lot of conventions on =
users we 
&gt; could not find a way to transform Twists without requiring a lot of ex=
tra 
&gt; information. 
&gt; 
&gt; There is an API to get the twist between two frames in the cturtle ver=
sion 
&gt; of tf. 
&gt; 
&gt; And kdl provides may twist manipulation methods which are recommended =
for 
&gt; computing things involving twists. 
&gt; 
&gt; If anyone else has input we can come back to this.=A0 I would like to =
add this 
&gt; capability, but building a consensus on representations will be requir=
ed. 
&gt; 
&gt; Tully 
&gt; 
&gt; On Mon, Jun 7, 2010 at 5:00 PM, Advait Jain &lt;<a href=3D"mailto:adva=
it at cc.gatech.edu">advait at cc.gatech.edu</a>&gt; wrote: 
&gt;&gt; 
&gt;&gt; I just realized that the wrench and twist messages currently 
&gt;&gt; do not explicitly store the point at which the wrench or twist 
&gt;&gt; is expressed. 
&gt;&gt; 
&gt;&gt; Is there is support in TF or somewhere else for getting the 
&gt;&gt; equivalent twist or wrench at a different point in space? 
&gt;&gt; 
&gt;&gt; e.g. to get the equivalent wrench at point B given a wrench 
&gt;&gt; acting at point A, I would use: 
&gt;&gt; Force at point A =3D Force at point B 
&gt;&gt; Torque at point A =A0=3D vector from A to B X Force + Torque at po=
int B 
&gt;&gt; 
&gt;&gt; It would be nice to have easy ways to be able to say, for 
&gt;&gt; example, that given a force that the robot is applying at the 
&gt;&gt; door handle, what the torque is at the hinge of the door. 
&gt;&gt; 
&gt;&gt; Another example could be if the we want a robot to perform 
&gt;&gt; a bi-manual and need to compute the motion of two points 
&gt;&gt; on the same rigid body. 
&gt;&gt; 
&gt;&gt; I think it would be really cool if TF could also shift twists, 
&gt;&gt; wrenches correctly in addition to changing coordinate frames. 
&gt;&gt; 
&gt;&gt; What are other people&#39;s thoughts about this? 
&gt;&gt; 
&gt;&gt; 
&gt;&gt; Advait 
&gt;&gt; _______________________________________________ 
&gt;&gt; ros-users mailing list 
&gt;&gt; <a href=3D"mailto:ros-users at code.ros.org">ros-users at code.ros.org</=
a> 
&gt;&gt; <a href=3D"https://code.ros.org/mailman/listinfo/ros-users" target=
=3D"_blank">https://code.ros.org/mailman/listinfo/ros-users</a> 
&gt; 
&gt; 
&gt; 
&gt; -- 
&gt; Tully Foote 
&gt; Systems Engineer 
&gt; Willow Garage, Inc. 
&gt; <a href=3D"mailto:tfoote at willowgarage.com">tfoote at willowgarage.com</a>=
 
&gt; (650) 475-2827 
&gt; 
&gt; _______________________________________________ 
&gt; ros-users mailing list 
&gt; <a href=3D"mailto:ros-users at code.ros.org">ros-users at code.ros.org</a><b=
r>
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_blank">https://code.ros.org/mailman/listinfo/ros-users</a> 
&gt; 
&gt; 
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</div></div></blockquote></div> -- Tully Foote=
 Systems Engineer Willow Garage, Inc. <a href=3D"mailto:tfoote at wil=
lowgarage.com">tfoote at willowgarage.com</a> (650) 475-2827 
</div>

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