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#include "btMultiBodyTreeCreator.hpp"
namespace btInverseDynamics
{
btMultiBodyTreeCreator::btMultiBodyTreeCreator() : m_initialized(false) {}
int btMultiBodyTreeCreator::createFromBtMultiBody(const btMultiBody *btmb, const bool verbose)
{
if (0x0 == btmb)
{
bt_id_error_message("cannot create MultiBodyTree from null pointer\n");
return -1;
}
// in case this is a second call, discard old data
m_data.clear();
m_initialized = false;
// btMultiBody treats base link separately
m_data.resize(1 + btmb->getNumLinks());
// add base link data
{
LinkData &link = m_data[0];
link.parent_index = -1;
if (btmb->hasFixedBase())
{
link.joint_type = FIXED;
}
else
{
link.joint_type = FLOATING;
}
btTransform transform = (btmb->getBaseWorldTransform());
//compute inverse dynamics in body-fixed frame
transform.setIdentity();
link.parent_r_parent_body_ref(0) = transform.getOrigin()[0];
link.parent_r_parent_body_ref(1) = transform.getOrigin()[1];
link.parent_r_parent_body_ref(2) = transform.getOrigin()[2];
link.body_T_parent_ref(0, 0) = transform.getBasis()[0][0];
link.body_T_parent_ref(0, 1) = transform.getBasis()[0][1];
link.body_T_parent_ref(0, 2) = transform.getBasis()[0][2];
link.body_T_parent_ref(1, 0) = transform.getBasis()[1][0];
link.body_T_parent_ref(1, 1) = transform.getBasis()[1][1];
link.body_T_parent_ref(1, 2) = transform.getBasis()[1][2];
link.body_T_parent_ref(2, 0) = transform.getBasis()[2][0];
link.body_T_parent_ref(2, 1) = transform.getBasis()[2][1];
link.body_T_parent_ref(2, 2) = transform.getBasis()[2][2];
// random unit vector. value not used for fixed or floating joints.
link.body_axis_of_motion(0) = 0;
link.body_axis_of_motion(1) = 0;
link.body_axis_of_motion(2) = 1;
link.mass = btmb->getBaseMass();
// link frame in the center of mass
link.body_r_body_com(0) = 0;
link.body_r_body_com(1) = 0;
link.body_r_body_com(2) = 0;
// BulletDynamics uses body-fixed frame in the cog, aligned with principal axes
link.body_I_body(0, 0) = btmb->getBaseInertia()[0];
link.body_I_body(0, 1) = 0.0;
link.body_I_body(0, 2) = 0.0;
link.body_I_body(1, 0) = 0.0;
link.body_I_body(1, 1) = btmb->getBaseInertia()[1];
link.body_I_body(1, 2) = 0.0;
link.body_I_body(2, 0) = 0.0;
link.body_I_body(2, 1) = 0.0;
link.body_I_body(2, 2) = btmb->getBaseInertia()[2];
// shift reference point to link origin (in joint axis)
mat33 tilde_r_com = tildeOperator(link.body_r_body_com);
link.body_I_body = link.body_I_body - link.mass * tilde_r_com * tilde_r_com;
if (verbose)
{
id_printf(
"base: mass= %f, bt_inertia= [%f %f %f]\n"
"Io= [%f %f %f;\n"
" %f %f %f;\n"
" %f %f %f]\n",
link.mass, btmb->getBaseInertia()[0], btmb->getBaseInertia()[1],
btmb->getBaseInertia()[2], link.body_I_body(0, 0), link.body_I_body(0, 1),
link.body_I_body(0, 2), link.body_I_body(1, 0), link.body_I_body(1, 1),
link.body_I_body(1, 2), link.body_I_body(2, 0), link.body_I_body(2, 1),
link.body_I_body(2, 2));
}
}
for (int bt_index = 0; bt_index < btmb->getNumLinks(); bt_index++)
{
if (verbose)
{
id_printf("bt->id: converting link %d\n", bt_index);
}
const btMultibodyLink &bt_link = btmb->getLink(bt_index);
LinkData &link = m_data[bt_index + 1];
link.parent_index = bt_link.m_parent + 1;
link.mass = bt_link.m_mass;
if (verbose)
{
id_printf("mass= %f\n", link.mass);
}
// from this body's pivot to this body's com in this body's frame
link.body_r_body_com[0] = bt_link.m_dVector[0];
link.body_r_body_com[1] = bt_link.m_dVector[1];
link.body_r_body_com[2] = bt_link.m_dVector[2];
if (verbose)
{
id_printf("com= %f %f %f\n", link.body_r_body_com[0], link.body_r_body_com[1],
link.body_r_body_com[2]);
}
// BulletDynamics uses a body-fixed frame in the CoM, aligned with principal axes
link.body_I_body(0, 0) = bt_link.m_inertiaLocal[0];
link.body_I_body(0, 1) = 0.0;
link.body_I_body(0, 2) = 0.0;
link.body_I_body(1, 0) = 0.0;
link.body_I_body(1, 1) = bt_link.m_inertiaLocal[1];
link.body_I_body(1, 2) = 0.0;
link.body_I_body(2, 0) = 0.0;
link.body_I_body(2, 1) = 0.0;
link.body_I_body(2, 2) = bt_link.m_inertiaLocal[2];
// shift reference point to link origin (in joint axis)
mat33 tilde_r_com = tildeOperator(link.body_r_body_com);
link.body_I_body = link.body_I_body - link.mass * tilde_r_com * tilde_r_com;
if (verbose)
{
id_printf(
"link %d: mass= %f, bt_inertia= [%f %f %f]\n"
"Io= [%f %f %f;\n"
" %f %f %f;\n"
" %f %f %f]\n",
bt_index, link.mass, bt_link.m_inertiaLocal[0], bt_link.m_inertiaLocal[1],
bt_link.m_inertiaLocal[2], link.body_I_body(0, 0), link.body_I_body(0, 1),
link.body_I_body(0, 2), link.body_I_body(1, 0), link.body_I_body(1, 1),
link.body_I_body(1, 2), link.body_I_body(2, 0), link.body_I_body(2, 1),
link.body_I_body(2, 2));
}
// transform for vectors written in parent frame to this link's body-fixed frame
btMatrix3x3 basis = btTransform(bt_link.m_zeroRotParentToThis).getBasis();
link.body_T_parent_ref(0, 0) = basis[0][0];
link.body_T_parent_ref(0, 1) = basis[0][1];
link.body_T_parent_ref(0, 2) = basis[0][2];
link.body_T_parent_ref(1, 0) = basis[1][0];
link.body_T_parent_ref(1, 1) = basis[1][1];
link.body_T_parent_ref(1, 2) = basis[1][2];
link.body_T_parent_ref(2, 0) = basis[2][0];
link.body_T_parent_ref(2, 1) = basis[2][1];
link.body_T_parent_ref(2, 2) = basis[2][2];
if (verbose)
{
id_printf(
"body_T_parent_ref= %f %f %f\n"
" %f %f %f\n"
" %f %f %f\n",
basis[0][0], basis[0][1], basis[0][2], basis[1][0], basis[1][1], basis[1][2],
basis[2][0], basis[2][1], basis[2][2]);
}
switch (bt_link.m_jointType)
{
case btMultibodyLink::eRevolute:
link.joint_type = REVOLUTE;
if (verbose)
{
id_printf("type= revolute\n");
}
link.body_axis_of_motion(0) = bt_link.m_axes[0].m_topVec[0];
link.body_axis_of_motion(1) = bt_link.m_axes[0].m_topVec[1];
link.body_axis_of_motion(2) = bt_link.m_axes[0].m_topVec[2];
// for revolute joints, m_eVector = parentComToThisPivotOffset
// m_dVector = thisPivotToThisComOffset
// from parent com to pivot, in parent frame
link.parent_r_parent_body_ref(0) = bt_link.m_eVector[0];
link.parent_r_parent_body_ref(1) = bt_link.m_eVector[1];
link.parent_r_parent_body_ref(2) = bt_link.m_eVector[2];
break;
case btMultibodyLink::ePrismatic:
link.joint_type = PRISMATIC;
if (verbose)
{
id_printf("type= prismatic\n");
}
link.body_axis_of_motion(0) = bt_link.m_axes[0].m_bottomVec[0];
link.body_axis_of_motion(1) = bt_link.m_axes[0].m_bottomVec[1];
link.body_axis_of_motion(2) = bt_link.m_axes[0].m_bottomVec[2];
// for prismatic joints, eVector
// according to documentation :
// parentComToThisComOffset
// but seems to be: from parent's com to parent's
// pivot ??
// m_dVector = thisPivotToThisComOffset
link.parent_r_parent_body_ref(0) = bt_link.m_eVector[0];
link.parent_r_parent_body_ref(1) = bt_link.m_eVector[1];
link.parent_r_parent_body_ref(2) = bt_link.m_eVector[2];
break;
case btMultibodyLink::eSpherical:
link.joint_type = SPHERICAL;
link.parent_r_parent_body_ref(0) = bt_link.m_eVector[0];
link.parent_r_parent_body_ref(1) = bt_link.m_eVector[1];
link.parent_r_parent_body_ref(2) = bt_link.m_eVector[2];
// random unit vector
link.body_axis_of_motion(0) = 0;
link.body_axis_of_motion(1) = 1;
link.body_axis_of_motion(2) = 0;
break;
case btMultibodyLink::ePlanar:
bt_id_error_message("planar joints not implemented\n");
return -1;
case btMultibodyLink::eFixed:
link.joint_type = FIXED;
// random unit vector
link.body_axis_of_motion(0) = 0;
link.body_axis_of_motion(1) = 0;
link.body_axis_of_motion(2) = 1;
// for fixed joints, m_dVector = thisPivotToThisComOffset;
// m_eVector = parentComToThisPivotOffset;
link.parent_r_parent_body_ref(0) = bt_link.m_eVector[0];
link.parent_r_parent_body_ref(1) = bt_link.m_eVector[1];
link.parent_r_parent_body_ref(2) = bt_link.m_eVector[2];
break;
default:
bt_id_error_message("unknown btMultiBody::eFeatherstoneJointType %d\n",
bt_link.m_jointType);
return -1;
}
if (link.parent_index > 0)
{ // parent body isn't the root
const btMultibodyLink &bt_parent_link = btmb->getLink(link.parent_index - 1);
// from parent pivot to parent com, in parent frame
link.parent_r_parent_body_ref(0) += bt_parent_link.m_dVector[0];
link.parent_r_parent_body_ref(1) += bt_parent_link.m_dVector[1];
link.parent_r_parent_body_ref(2) += bt_parent_link.m_dVector[2];
}
else
{
// parent is root body. btMultiBody only knows 6-DoF or 0-DoF root bodies,
// whose link frame is in the CoM (ie, no notion of a pivot point)
}
if (verbose)
{
id_printf("parent_r_parent_body_ref= %f %f %f\n", link.parent_r_parent_body_ref[0],
link.parent_r_parent_body_ref[1], link.parent_r_parent_body_ref[2]);
}
}
m_initialized = true;
return 0;
}
int btMultiBodyTreeCreator::getNumBodies(int *num_bodies) const
{
if (false == m_initialized)
{
bt_id_error_message("btMultiBody not converted yet\n");
return -1;
}
*num_bodies = static_cast<int>(m_data.size());
return 0;
}
int btMultiBodyTreeCreator::getBody(const int body_index, int *parent_index, JointType *joint_type,
vec3 *parent_r_parent_body_ref, mat33 *body_T_parent_ref,
vec3 *body_axis_of_motion, idScalar *mass,
vec3 *body_r_body_com, mat33 *body_I_body, int *user_int,
void **user_ptr) const
{
if (false == m_initialized)
{
bt_id_error_message("MultiBodyTree not created yet\n");
return -1;
}
if (body_index < 0 || body_index >= static_cast<int>(m_data.size()))
{
bt_id_error_message("index out of range (got %d but only %zu bodies)\n", body_index,
m_data.size());
return -1;
}
*parent_index = m_data[body_index].parent_index;
*joint_type = m_data[body_index].joint_type;
*parent_r_parent_body_ref = m_data[body_index].parent_r_parent_body_ref;
*body_T_parent_ref = m_data[body_index].body_T_parent_ref;
*body_axis_of_motion = m_data[body_index].body_axis_of_motion;
*mass = m_data[body_index].mass;
*body_r_body_com = m_data[body_index].body_r_body_com;
*body_I_body = m_data[body_index].body_I_body;
*user_int = -1;
*user_ptr = 0x0;
return 0;
}
} // namespace btInverseDynamics
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