KDL::Segment::pose

Submitted by threelight on Mon, 2008-09-15 13:33.

is the input value of Frame KDL::Segment::pose (const double & q ) const a deg or a rad value?

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Ruben Smits's picture

KDL::Segment::pose

Submitted by Ruben Smits on Mon, 2008-09-15 13:45.

On Monday 15 September 2008 15:33:33 manuelbirlo [..] wrote:
> is the input value of Frame KDL::Segment::pose (const double & q ) const
> a deg or a rad value?

it depends on the type of joint in the root of the segment. For translational
joints this is meter, for rotational joints it is radians.

Ruben

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KDL::Segment::pose

Submitted by threelight on Mon, 2008-10-06 10:09.

are the frames which you get from this function expressed in world coordinates or in relative coordinates?

example:
If I want to get the current z-axis of joint 2 for joint angle 0: 

 KDL::Segment seg = chain.getSegment(1);
 KDL::Frame f;
 f = segment.pose(0.0);
 KDL::Vector z_axis;
 z_axis(0) = f(0,2);
 z_axis(1) = f(1,2);
 z_axis(2) = f(2,2);

does f now contains the current z-axis with respect to the base frame or with respect to the previous frame?

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Ruben Smits's picture

KDL::Segment::pose

Submitted by Ruben Smits on Mon, 2008-10-06 13:50.

On Monday 06 October 2008 12:09:20 manuelbirlo [..] wrote:
> are the frames which you get from this function expressed in world
> coordinates or in relative coordinates?

They are in the base-frame of the segment, since a segment has no idea were it
is positioned in the world frame

> example:
> If I want to get the current z-axis of joint 2 for joint angle 0:
>
> KDL::Segment seg = chain.getSegment(1);
> KDL::Frame f;
> f = segment.pose(0.0);
> KDL::Vector z_axis;
You could have written: KDL::Vector z_axis=f.M.UnitZ(), which is a much nicer
way of accessing the underlying axes of the rotation of a frame.
see
<http://people.mech.kuleuven.be/~rsmits/kdl/api/html/classKDL_1_1Rotation.html>

> z_axis(0) = f(0,2);
> z_axis(1) = f(1,2);
> z_axis(2) = f(2,2);
>
> does f now contains the current z-axis with respect to the base frame or
> with respect to the previous frame?

it is the z-axis of the tip of the segment with respect to the base of the
segment.

Ruben

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