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Query in turtlesim tf tutorials.

asked 2016-10-28 19:29:02 -0500

kartikmadhira1 gravatar image

I am currently going through the tf tutorials and have a doubt in particular in the tf listener. In the code

while(n.ok())
  {
    tf::StampedTransform tf;
    try{
      listen.lookupTransform("/turtle2","/turtle1",ros::Time(0),tf);
        }

What does turtle1 to turtle2 frame transformation mean? The turtle1 frame is already transformed to the world frame in the tf broadcaster?

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answered 2016-10-29 18:27:35 -0500

tfoote gravatar image

The tf::Listener builds up a cache of the published transforms for all the tf::Broadcasters. The lookupTransform method then traverses the cache at a specific time between two specific coordinate frames requested.

It is required that there is a chain of links with defined transforms between turtle1 and turtle2 to complete the lookupTransform call. In this example they connect through the world frame. lookupTransform works for any two connected links.

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So basically, when there is a lookupTransform between turtle1 and turtle2 it is traversing from turtle1->world and then world->turtle2 or vice-versa?

kartikmadhira1 gravatar image kartikmadhira1  ( 2016-10-29 18:43:30 -0500 )edit

Also, when we are using the set setOrigin using the tf::Transform object, what exactly does it set origin or translations with respect to(frame). For example in the tutorials, we've set translations and rotations of turtle's pose. But these co-ordinates are with respect to what?

kartikmadhira1 gravatar image kartikmadhira1  ( 2016-10-29 18:47:11 -0500 )edit

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Asked: 2016-10-28 19:29:02 -0500

Seen: 86 times

Last updated: Oct 29 '16