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output velocity and angular velocity in a ModelTask's link export #31

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Jan 10, 2017
Merged

output velocity and angular velocity in a ModelTask's link export #31

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7f0e4e5
output velocity and angular velocity in a ModelTask's link export
doudou Dec 30, 2016
ee87c85
generate body-fixed angular velocities as documented for RigidBodyState
doudou Jan 6, 2017
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16 changes: 16 additions & 0 deletions tasks/ModelTask.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -243,20 +243,36 @@ void ModelTask::updateLinks(base::Time const& time)
}

math::Pose source2world = math::Pose::Zero;
math::Vector3 sourceInWorld_linear_vel = math::Vector3::Zero;
math::Vector3 source_angular_vel;
if (it->second.source_link_ptr)
{
source2world = it->second.source_link_ptr->GetWorldPose();
sourceInWorld_linear_vel = it->second.source_link_ptr->GetWorldLinearVel();
source_angular_vel = it->second.source_link_ptr->GetRelativeAngularVel();
}

math::Pose target2world = math::Pose::Zero;
if (it->second.target_link_ptr)
target2world = it->second.target_link_ptr->GetWorldPose();

math::Pose source2target( math::Pose(source2world - target2world) );
math::Vector3 sourceInTarget_linear_vel (target2world.rot.RotateVectorReverse(sourceInWorld_linear_vel));
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It should not consider the velocities of the targetInWorld as well?
(I know that the target frame is usually a fixed point, but is this always the case?)

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I know that the target frame is usually a fixed point, but is this always the case?

I elected to generate the velocity of the source frame within the target frame considered-as a fixed frame at time t. Part for simplicity reasons, part because it's a possible convention, part because then one can use it with sourceFrame==targetFrame to get both velocities expressed in the body frame.

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Alright.

I just have doubt about the use of sourceFrame==targetFrame.
It means that we interpret the velocities as absolute (velocities of the sourceFrame related to a inertial frame, not the targetFrame) and represent them in targetFrame (for linear case) and sourceFrame (angular case).

The relative velocities of the sourceFrame related to the targetFrame should be zero if they are the same.


RigidBodyState rbs;
rbs.sourceFrame = it->second.source_frame;
rbs.targetFrame = it->second.target_frame;
rbs.position = base::Vector3d(
source2target.pos.x,source2target.pos.y,source2target.pos.z);
rbs.cov_position = _cov_position;
rbs.orientation = base::Quaterniond(
source2target.rot.w,source2target.rot.x,source2target.rot.y,source2target.rot.z );
rbs.cov_orientation = _cov_orientation;
rbs.velocity = base::Vector3d(
sourceInTarget_linear_vel.x,sourceInTarget_linear_vel.y,sourceInTarget_linear_vel.z);
rbs.cov_velocity = _cov_velocity;
rbs.angular_velocity = base::Vector3d(
source_angular_vel.x,source_angular_vel.y,source_angular_vel.z);
rbs.time = time;
it->second.port->write(rbs);
it->second.last_update = time;
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