Find coordinates of point in a different coordinate frame

Question

Hi,

I would like to know the easiest ROS way (tf, geometry_msgs or something of the sort) to get the coordinates of a point in another coordinate frame defined by a pose.

Let's say, I have a point w coordinates x, y, z in a global frame and I have a pose of a local coordinate frame wrt the same global frame in the form of a geometry_msgs/Pose. Now how do I find x1, y1, z1 which are the coordinates of that point in the local coordinate frame (given by that pose)

Thank you.

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Originally posted by 2ROS0 on ROS Answers with karma: 1133 on 2016-07-25

Post score: 2

Answer 1

@2ROS0: "(I don't want to do that for some smaller tasks)" Exactly the same with me.

I am looking for an API programming language equivalent of $ rosrun tf tf_echo [frame1] [frame2]

I'm also trying to see how this command works:

void transformPoint (const std::string &target_frame, const Stamped< tf::Point > &stamped_in, Stamped< tf::Point > &stamped_out) const

but I don't see an indication for the current/reference frame which is not too good.

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Originally posted by BluPlana with karma: 26 on 2017-02-23

This answer was ACCEPTED on the original site

Post score: 0

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Original comments

Comment by gvdhoorn on 2017-02-24:\

I don't see an indication for the current/reference frame

The input to transformPoint(..) is a Stamped<tf::Point>. Stamped in ROS parlance means: "with a header", which implies that the frame_id of the hdr is valid. That is the source frame. target_frame is the .. target.

Comment by gvdhoorn on 2017-02-24:
Note: the Stamped suffix is used on msgs to indicate that it has a Header. In this case the terminology / naming convention was carried over, but Stamped is not a msg def. Member names are identical though: api/Stamped.

Comment by BluPlana on 2017-02-24:
@gvdhoorn: Thanks. Your response is really helpful!

for points that are not stamped, what happens?

Comment by BluPlana on 2017-02-24:
However, for points without stamps, how does one know the operating frame? My point doesn't have any stamp, but I'm sure it is defined in the /world. However, when I perform Inverse kinematics on my KDL chain to that point, my IK_solver seems to take the endeff to the point in the chain_root_frame

Comment by gvdhoorn on 2017-02-24:\

for points that are not stamped, what happens?

well, for this particular overload you'll get a compiler error.

But in general you'll have to either convert your Point to a Stamped version (ie: by providing the required info), or use one of the more suited overloads.