/*************************************************************************
* *
* Open Dynamics Engine, Copyright (C) 2001,2002 Russell L. Smith. *
* All rights reserved. Email: russ@q12.org Web: www.q12.org *
* *
* This library is free software; you can redistribute it and/or *
* modify it under the terms of EITHER: *
* (1) The GNU Lesser General Public License as published by the Free *
* Software Foundation; either version 2.1 of the License, or (at *
* your option) any later version. The text of the GNU Lesser *
* General Public License is included with this library in the *
* file LICENSE.TXT. *
* (2) The BSD-style license that is included with this library in *
* the file LICENSE-BSD.TXT. *
* *
* This library is distributed in the hope that it will be useful, *
* but WITHOUT ANY WARRANTY; without even the implied warranty of *
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the files *
* LICENSE.TXT and LICENSE-BSD.TXT for more details. *
* *
*************************************************************************/
/*
test that the rotational physics is correct.
an "anchor body" has a number of other randomly positioned bodies
("particles") attached to it by ball-and-socket joints, giving it some
random effective inertia tensor. the effective inertia matrix is calculated,
and then this inertia is assigned to another "test" body. a random torque is
applied to both bodies and the difference in angular velocity and orientation
is observed after a number of iterations.
typical errors for each test cycle are about 1e-5 ... 1e-4.
*/
#include <time.h>
#include <ode/ode.h>
#include <drawstuff/drawstuff.h>
#ifdef _MSC_VER
#pragma warning(disable:4244 4305) // for VC++, no precision loss complaints
#endif
// select correct drawing functions
#ifdef dDOUBLE
#define dsDrawBox dsDrawBoxD
#define dsDrawSphere dsDrawSphereD
#define dsDrawCylinder dsDrawCylinderD
#define dsDrawCappedCylinder dsDrawCappedCylinderD
#endif
// some constants
#define NUM 10 // number of particles
#define SIDE 0.1 // visual size of the particles
// dynamics objects an globals
static dWorldID world=0;
static dBodyID anchor_body,particle[NUM],test_body;
static dJointID particle_joint[NUM];
static dReal torque[3];
static int iteration;
// start simulation - set viewpoint
static void start()
{
static float xyz[3] = {1.5572f,-1.8886f,1.5700f};
static float hpr[3] = {118.5000f,-17.0000f,0.0000f};
dsSetViewpoint (xyz,hpr);
}
// compute the mass parameters of a particle set. q = particle positions,
// pm = particle masses
#define _I(i,j) I[(i)*4+(j)]
void computeMassParams (dMass *m, dReal q[NUM][3], dReal pm[NUM])
{
int i,j;
dMassSetZero (m);
for (i=0; i<NUM; i++) {
m->mass += pm[i];
for (j=0; j<3; j++) m->c[j] += pm[i]*q[i][j];
m->_I(0,0) += pm[i]*(q[i][1]*q[i][1] + q[i][2]*q[i][2]);
m->_I(1,1) += pm[i]*(q[i][0]*q[i][0] + q[i][2]*q[i][2]);
m->_I(2,2) += pm[i]*(q[i][0]*q[i][0] + q[i][1]*q[i][1]);
m->_I(0,1) -= pm[i]*(q[i][0]*q[i][1]);
m->_I(0,2) -= pm[i]*(q[i][0]*q[i][2]);
m->_I(1,2) -= pm[i]*(q[i][1]*q[i][2]);
}
for (j=0; j<3; j++) m->c[j] /= m->mass;
m->_I(1,0) = m->_I(0,1);
m->_I(2,0) = m->_I(0,2);
m->_I(2,1) = m->_I(1,2);
}
void reset_test()
{
int i;
dMass m,anchor_m;
dReal q[NUM][3], pm[NUM]; // particle positions and masses
dReal pos1[3] = {1,0,1}; // point of reference (POR)
dReal pos2[3] = {-1,0,1}; // point of reference (POR)
// make random particle positions (relative to POR) and masses
for (i=0; i<NUM; i++) {
pm[i] = dRandReal()+0.1;
q[i][0] = dRandReal()-0.5;
q[i][1] = dRandReal()-0.5;
q[i][2] = dRandReal()-0.5;
}
// adjust particle positions so centor of mass = POR
computeMassParams (&m,q,pm);
for (i=0; i<NUM; i++) {
q[i][0] -= m.c[0];
q[i][1] -= m.c[1];
q[i][2] -= m.c[2];
}
if (world) dWorldDestroy (world);
world = dWorldCreate();
anchor_body = dBodyCreate (world);
dBodySetPosition (anchor_body,pos1[0],pos1[1],pos1[2]);
dMassSetBox (&anchor_m,1,SIDE,SIDE,SIDE);
dMassAdjust (&anchor_m,0.1);
dBodySetMass (anchor_body,&anchor_m);
for (i=0; i<NUM; i++) {
particle[i] = dBodyCreate (world);
dBodySetPosition (particle[i],
pos1[0]+q[i][0],pos1[1]+q[i][1],pos1[2]+q[i][2]);
dMassSetBox (&m,1,SIDE,SIDE,SIDE);
dMassAdjust (&m,pm[i]);
dBodySetMass (particle[i],&m);
}
for (i=0; i < NUM; i++) {
particle_joint[i] = dJointCreateBall (world,0);
dJointAttach (particle_joint[i],anchor_body,particle[i]);
const dReal *p = dBodyGetPosition (particle[i]);
dJointSetBallAnchor (particle_joint[i],p[0],p[1],p[2]);
}
// make test_body with the same mass and inertia of the anchor_body plus
// all the particles
test_body = dBodyCreate (world);
dBodySetPosition (test_body,pos2[0],pos2[1],pos2[2]);
computeMassParams (&m,q,pm);
m.mass += anchor_m.mass;
for (i=0; i<12; i++) m.I[i] = m.I[i] + anchor_m.I[i];
dBodySetMass (test_body,&m);
// rotate the test and anchor bodies by a random amount
dQuaternion qrot;
for (i=0; i<4; i++) qrot[i] = dRandReal()-0.5;
dNormalize4 (qrot);
dBodySetQuaternion (anchor_body,qrot);
dBodySetQuaternion (test_body,qrot);
dMatrix3 R;
dQtoR (qrot,R);
for (i=0; i<NUM; i++) {
dVector3 v;
dMultiply0 (v,R,&q[i][0],3,3,1);
dBodySetPosition (particle[i],pos1[0]+v[0],pos1[1]+v[1],pos1[2]+v[2]);
}
// set random torque
for (i=0; i<3; i++) torque[i] = (dRandReal()-0.5) * 0.1;
iteration=0;
}
// simulation loop
static void simLoop (int pause)
{
if (!pause) {
dBodyAddTorque (anchor_body,torque[0],torque[1],torque[2]);
dBodyAddTorque (test_body,torque[0],torque[1],torque[2]);
dWorldStep (world,0.03);
iteration++;
if (iteration >= 100) {
// measure the difference between the anchor and test bodies
const dReal *w1 = dBodyGetAngularVel (anchor_body);
const dReal *w2 = dBodyGetAngularVel (test_body);
const dReal *q1 = dBodyGetQuaternion (anchor_body);
const dReal *q2 = dBodyGetQuaternion (test_body);
dReal maxdiff = dMaxDifference (w1,w2,1,3);
printf ("w-error = %.4e (%.2f,%.2f,%.2f) and (%.2f,%.2f,%.2f)\n",
maxdiff,w1[0],w1[1],w1[2],w2[0],w2[1],w2[2]);
maxdiff = dMaxDifference (q1,q2,1,4);
printf ("q-error = %.4e\n",maxdiff);
reset_test();
}
}
dReal sides[3] = {SIDE,SIDE,SIDE};
dReal sides2[3] = {6*SIDE,6*SIDE,6*SIDE};
dReal sides3[3] = {3*SIDE,3*SIDE,3*SIDE};
dsSetColor (1,1,1);
dsDrawBox (dBodyGetPosition(anchor_body), dBodyGetRotation(anchor_body),
sides3);
dsSetColor (1,0,0);
dsDrawBox (dBodyGetPosition(test_body), dBodyGetRotation(test_body), sides2);
dsSetColor (1,1,0);
for (int i=0; i<NUM; i++)
dsDrawBox (dBodyGetPosition (particle[i]),
dBodyGetRotation (particle[i]), sides);
}
int main (int argc, char **argv)
{
// setup pointers to drawstuff callback functions
dsFunctions fn;
fn.version = DS_VERSION;
fn.start = &start;
fn.step = &simLoop;
fn.command = 0;
fn.stop = 0;
fn.path_to_textures = "../../drawstuff/textures";
if(argc==2)
{
fn.path_to_textures = argv[1];
}
dRandSetSeed (time(0));
reset_test();
// run simulation
dsSimulationLoop (argc,argv,352,288,&fn);
dWorldDestroy (world);
return 0;
}
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