1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
|
/*************************************************************************
* *
* 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>
#include "texturepath.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 dsDrawCapsule dsDrawCapsuleD
#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()
{
dAllocateODEDataForThread(dAllocateMaskAll);
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_TEXTURE_PATH;
dInitODE2(0);
dRandSetSeed (time(0));
reset_test();
// run simulation
dsSimulationLoop (argc,argv,352,288,&fn);
dWorldDestroy (world);
dCloseODE();
return 0;
}
|
