Marsh D. Applied Geometry for Computer Graphics and CAD
Подождите немного. Документ загружается.
Solutions 339
9.13. Control points: (−1, 0, 1), (0, 0, 0), (1, 0, 1); (−1, −1, 1), (0, 0, 0), (1, 1, 1);
(1, −1, 1), (0, 0, 0), (−1, 1, 1); (1, 0, 1), (0, 0, 0), (−1, 0, 1); (1, 1, 1), (0, 0, 0),
(−1, −1, 1); (−1, 1, 1), (0, 0, 0), (1, −1, 1); (−1, 0, 1), (0, 0, 0), (1, 0, 1).
Weights: w
i,0
= w
i,2
= {1, 0.5, 0.5, 1, 0.5, 0.5, 1},
w
i,1
= {3, 1.5, 1.5, 3, 1.5, 1.5, 3}.
9.19.
(1 − s)(3t
2
+4, 2t
2
, −t)+s(2t, −t
4
, 2t +4)
=(4− 4s +2st +3t
2
− 3st
2
, 2t
2
− 2st
2
− st
4
, 4s − t +3st) .
9.20. (a)
(3(1 − 3s
2
+2s
3
)t
2
+(3s
2
− 2s
3
)(2t + 10) + s − 2s
2
+ s
3
,
2(1 − 3s
2
+2s
3
)t
2
+3(3s
2
− 2s
3
)t + s − s
2
,
(1 − 3s
2
+2s
3
)t +2(3s
2
− 2s
3
)t
2
)
=(3t
2
− 9t
2
s
2
+6t
2
s
3
+6ts
2
+28s
2
− 4ts
3
− 19s
3
+ s,
2t
2
− 6t
2
s
2
+4t
2
s
3
+9ts
2
− 6ts
3
+ s − s
2
,
t − 3ts
2
+2ts
3
+6t
2
s
2
− 4t
2
s
3
) .
(b)
3(1 − 3s
2
+2s
3
)t
2
+(3s
2
− 2s
3
)(2t + 10) + (s − 2s
2
+ s
3
)s,
2(1 − 3s
2
+2s
3
)t
2
+3(3s
2
− 2s
3
)t − 2s +4s
2
− 2s
3
− (−s
2
+ s
3
)s,
(1 − 3s
2
+2s
3
)t +2(3s
2
− 2s
3
)t
2
+(s − 2s
2
+ s
3
)s +2(−s
2
+ s
3
)s)
=(3t
2
− 9t
2
s
2
+6t
2
s
3
+6ts
2
+31s
2
− 4ts
3
− 22s
3
+ s
4
,
2t
2
− 6t
2
s
2
+4t
2
s
3
+9ts
2
− 6ts
3
− 2s +4s
2
− s
3
− s
4
,
t − 3ts
2
+2ts
3
+6t
2
s
2
− 4t
2
s
3
+ s
2
− 4s
3
+3s
4
.
340 Solutions
9.21.
5(1− s)(1− t) − 20 (1 − s) t +8s (1 − t) − 27 st +(1− s)(−5+25t)
+ s
−8(1− t)
2
+20(1− t) t +27t
2
+(1− t)
−5(1− s)
3
− 18 (1 − s)
2
s − 21 (1 − s) s
2
− 8 s
3
+ t
20 (1 − s)
2
+44(1− s) s +27s
2
,
5(1− s)(1− t) − 3(1− s) t − 7 st +(1− s)(−5+8t)
+ s
32 (1 − t) t +7t
2
+(1− t)
−5(1− s)
3
− 12 (1 − s)
2
s − 6(1− s) s
2
+ t
3(1− s)
2
+10(1− s) s +7s
2
,
− 10 s (1 − t) − 10 st + s
10 (1 − t)
2
+8(1− t) t +10t
2
+(1− t)
9(1− s)
2
s +21(1− s) s
2
+10s
3
+ t
8(1− s) s +10s
2
=(−5+25t − 3 s +8st − st
2
+3ts
2
,
− 5+8t +3s +26st − 25 st
2
+3s
2
− s
3
− 3 ts
2
+ ts
3
,
9 s − 13 st +12st
2
+3s
2
− 2 s
3
− ts
2
+2ts
3
) .
Chapter 10
10.1. (a) C
(t)=(1, sinh (t/c)), C
(t)=
0,
1
c
cosh (t/c)
,
t(t)=(1/ cosh (t/c) , tanh (t/c)), n(t)=(−tanh (t/c) , 1/ cosh (t/c)).
κ =1/c cosh
2
(t/c) .
10.3. (a) θ(s) = arcsin s,andx =
1
2
s
√
1 − s
2
+
1
2
arcsin s, y =
1
2
s
2
.(b)
θ(s)=2
√
s,andx =2
√
s sin (
√
s)cos(
√
s)+cos
2
(
√
s) − 1, y =
sin (
√
s)cos(
√
s) − 2
√
s cos
2
(
√
s)+
√
s.
(c) θ(s)=−arctan(s/a), and x = a ln((s +
√
a
2
+ s
2
)/a), y = a −
√
a
2
+ s
2
.
10.4. Reparametrize the curve so that C(s) is unit speed. If κ(s) = 0 for all
s,thenC
(s)=κ(s)N(s) implies that C
(s)=(0, 0). Thus C
(s)=
(a
1
,a
2
) for some constants a
1
and a
2
. Finally, integrating gives C(s)=
(a
1
s+b
1
,a
2
s+b
2
). The result can also be deduced from the fundamental
theorem of plane curves: θ =
κ(u) du =
0 du etc.
Solutions 341
10.5. In polar coordinates: (x, y)=(r(θ)cosθ, r(θ)sinθ). Then (x
,y
)=
(r
(θ)cosθ − r(θ)sinθ, r
(θ)sinθ + r(θ)cosθ). So the arclength is
b
a
(r
(θ)cosθ − r(θ)sinθ)
2
+(r
(θ)sinθ + r(θ)cosθ)
2
dθ
=
(r(θ)
2
+(r
(θ))
2
)dθ .
Further,
(x
,y
)=(r
(θ)cosθ − 2r
(θ)sinθ − r(θ)cosθ,
r
(θ)sinθ +2r
(θ)cosθ − r(θ)sinθ)
and substitution into the formula for curvature gives κ =
2(r
)
2
−rr
+r
2
(r
2
+(r
)
2
)
3/2
.
10.6. (a) κ =
1
2(2+2 cos t)
1/2
. E(t)=(t − sin t, 3+cost) .
(b)
˙
C(t)=(−a sin t, b cos t),
¨
C(t)=(−a cos t, −b sin t) .
n(t)=
−b cos t
√
a
2
sin
2
t+b
2
cos
2
t
,
−a sin t
√
a
2
sin
2
t+b
2
cos
2
t
,
κ(t)=
ab
(a
2
sin
2
t+b
2
cos
2
t)
3/2
.
Evolute is E(t)=
a
2
−b
2
a
cos
3
t, −
a
2
−b
2
b
sin
3
t
.
10.7. (a) Offset is (−3sint, 2cost)+
d
(9 sin
2
t+4 cos
2
t)
1/2
(−2cost, −3sint).
(b) κ(t)=
6
(4 sin
2
t+9 cos
2
t)
3/2
, ˙κ(t)=
90 sin t cos t
(4 sin
2
t+9 cos
2
t)
5/2
. Maxima and min-
ima occur when ˙κ(t) = 0. Hence t =0,π/2,π,3π/2 corresponding to the
points (3, 0), (0, 2), (−3, 0), (0, −2).
(c) Maximum and minimum values of curvature are
3
4
and
2
9
. Therefore
the maximum and minimum radii of curvature are
9
2
and
4
3
. Hence the
maximum radius the ball cutter can be is
9
2
, otherwise the cutter will
be too large to cut the ellipse at the points (0, 2) and (0, −2).
10.10.
˙
C(t)=(−4sint, −5cost, 3sint),
˙
C(t)
=5.
t =
−
4
5
sin t, −cos t,
3
5
sin t
. n =
−
4
5
cos t, sin t,
3
5
cos t
.
b =
−
3
5
, 0, −
4
5
. κ =1/5, τ = 0. Curve is a circle radius 5.
10.11. t =
−
3
10
sin t −
2
5
cos t,
3
10
cos t −
2
5
sin t,
√
3
2
,
n =
−
3
5
cos t +
4
5
sin t, −
3
5
sin t −
4
5
cos t, 0
,
b =
3
√
3
10
sin t +
2
√
3
5
cos t, −
3
√
3
10
cos t +
2
√
3
5
sin t,
1
2
.
342 Solutions
κ =1/20, τ =
√
3/20.
10.12. κ =
√
5
2
2 − cos
2
t
−3/2
, τ = 0. Curve is an ellipse.
10.13. (a) κ = τ =1/3(1 + t
2
)
2
.(b)κ =
1+cos
2
t
+1
1/2
/(3 + 2 cos t)
3/2
,
τ =1/
1+cos
2
t
+1
1/2
.(c)κ =
3
2
t
3
1+t
2
+ t
4
−3/2
, τ =0.
10.14. κ = τ =
1
2
2 − 2t
2
−1/2
.
10.17. (a) a =
√
17,b=13
√
2,c=39soκ =
26
867
√
2
√
17 = 0. 175, τ =
1
34
√
2
√
17 = 0. 171. (b) κ =0.185, τ =0.334.
10.24. (a) 2(1 + 4u
2
+4v
2
)
−1/2
and 2(1 + 4u
2
+4v
2
)
−3/2
.(c)r and cos u(R +
r cos u)
−1
.
10.25. (a) K = −(1 + u
2
+ v
2
)
−2
, H = −uv(1 + u
2
+ v
2
)
−3/2
.
10.26. (b) (0, 0, 0).
10.32.
1
π
π
0
k
max
cos
2
θ + k
min
sin
2
θ
dθ =
1
π
1
2
(θ +cosθ sin θ) k
max
+
1
2
(θ − cos θ sin θ) k
min
π
0
=
1
2
(k
max
+ k
min
).
Chapter 11
11.2. N =
1
√
1+4s
2
+4t
2
(2s, 2t, 1). So at (0.5, 0.5, −0.5), N =
1
√
3
(1, 1, −1).
The incident ray has direction (0, 10, 20) − (0.5, 0.5, −0.5), giving L =
−
√
227
681
,
19
√
227
681
,
41
√
227
681
. R =
−
43
√
227
2043
, −
103
√
227
2043
, −
77
√
227
2043
. The an-
gle of incidence is 1.272609737 radians.
11.4. V ·N =(0, 1, 0) ·(−t −2s, −s + t
2
, 1) = −s + t
2
. So the silhouette points
satisfy s = t
2
giving the curve
t
2
,t,
2
3
t
3
+ t
4
.
11.5. V · N =(1, 0, 0) · (1 − t
2
− s
2
, −2st, 1) = 1 − s
2
− t
2
. So the silhouette
points satisfy s
2
+ t
2
= 1 defining the unit circle in the (s, t)-plane.
The circle may be parametrized as (s, t)=(cosθ, sin θ) and substituting
into the parametric equation of the surface gives the silhouette curve
cos θ, sin θ, cos θ sin
2
θ − cos θ +1/3cos
3
θ
.
11.6. V · N =(0, 1, 0) · (−18st, 1 − 9s
2
+9t
2
, 1) = 1 − 9s
2
+9t
2
=0.
The substitution (s, t)=(
1
3
cosh θ,
1
3
sinh θ) gives the silhouette curve
1
3
cosh θ,
1
3
sinh θ,
1
3
cosh
2
θ sinh θ −
1
3
sinh θ −
1
9
sinh
3
θ
.
11.7. The plane ax + by + cz + d =0hasnormalN =(a, b, c). For a parallel
projection in the direction V(v
0
,v
1
,v
2
), V · N = av
0
+ bv
1
+ cv
2
.In
Solutions 343
general, av
0
+ bv
1
+ cv
2
= 0 and there are no silhouette points. When
av
0
+ bv
1
+ cv
2
= 0, every point is a silhouette point. (The condition
corresponds to when V is perpendicular to N).
For a perspective projection from the viewpoint V(v
0
,v
1
,v
2
), the con-
dition for a silhouette is (v
0
− x, v
1
− y, v
2
− z) · N = av
0
+ bv
1
+ cv
2
−
(ax + by + cz) = 0 giving av
0
+ bv
1
+ cv
2
+ d = 0. The condition is
satisfied if and only if V is a point on the plane and every point of the
plane is a silhouette point.
11.11. If the viewpoint V lies inside the sphere centred at C, radius r,then
|V − C| <r. Using Exercise 11.7.(a), d>rand r
1
, given by 11.7(b),
has no solution.
11.14. The silhouettes are two lines
1/λ, ±
(λ
1
− 1)/λ, t
.
11.15. V =(10, 0, 0, 1) and
Q =
⎛
⎜
⎜
⎜
⎜
⎜
⎝
40−10
010 0
−10−10
000−4
⎞
⎟
⎟
⎟
⎟
⎟
⎠
.
The silhouette plane is: 40x−10z −4 = 0. Solving for x and substituting
into the equation of the quadric gives the conic: −
99
25
− 5/4 z
2
+ y
2
=0
which can be parametrized by
(y, z)=
±
99/25 cosh t,
396/125 sinh t
.
A parametrization for the silhouette follows.
11.17. V =(0, 0, 1), N =(−f(u)g
(u)cosv, −f(u)g
(u)sinv, f(u)f
(u)) and
V ·N = f(u)f
(u) = 0. Since f(u) = 0 silhouette points satisfy f
(u)=
0. For each u
0
such that f
(u
0
) = 0 there is a silhouette circle given by
(f(u
0
)cosv, f(u
0
)sinv, g(u
0
)).
11.18. Since VQP
T
is a 1 × 1 matrix it is equal to its own transpose, namely,
PQV
T
.
11.20.
VQP
T
=
λ 001
⎛
⎜
⎜
⎝
100 0
010 0
000 0
000−1
⎞
⎟
⎟
⎠
⎛
⎜
⎜
⎝
x
y
z
1
⎞
⎟
⎟
⎠
= λx − 1=0.
Therefore x =
1
λ
and y = ±
√
λ
2
−1
λ
giving two lines (
1
λ
, ±
√
λ
2
−1
λ
,z).
References
[1] Abhyankar, S S and Bajaj, C, ‘Automatic parametrization of rational
curves and surfaces I: Conics and conicoids. Computer-Aided Design Vol.
19, pp11–14, 1987.
[2] B´ezier, P, ‘Style, mathematics and NC’. Computer-Aided Design Vol. 22
No. 9, pp523–526, 1990.
[3] Boehm, W and Prautzsch, H, ‘The insertion algorithm’. Computer-Aided
Design Vol. 17 No. 2, pp58–59, 1985.
[4] Braid, I C, Hillyard, R C, and Stroud I A, ‘Stepwise construction of polhe-
dra in geometric modelling’ in Mathematical Methods in Computer Graph-
ics and Design, ed. K W Brodlie, pp123-141, Academic Press, 1980.
[5] Coolidge, J L, A History of the Conic Sections and Quadric Surfaces.
OUP, 1945.
[6] Davis, P, ‘B-splines and geometric design’, SIAM News Vol. 29 No. 5,
1996.
[7] Dill, J. ‘An application of colour graphics to the display of surface curva-
ture’. Computer Graphics Vol. 15, pp153–161, 1981.
[8] Do Carmo, M P, Differential Geometry of Curves and Surfaces. Prentice-
Hall, 1976.
[9] Farin, G, Curves and Surfaces for Computer-Aided Geometric Design.
Third Edition. Academic Press, 1993.
[10] Forrest, A R, ‘Interactive interpolation and approximation by B´ezier poly-
nomials’, Computer-Aided Design Vol. 22 No. 9, pp527–537, 1990. Origi-
nally published in The Computer Journal Vol. 15 No. 1, pp71–79, 1972.
345
346 References
[11] Gibson, C.G., Elementary Geometry of Algebraic Curves. Cambridge Uni-
versity Press, 1998.
[12] Haralick, R M and Shapiro, L G, Computer and Robot Vision. Addison-
Wesley, 1992.
[13] Hoschek, J and Lasser, D, Fundamentals of Computer Aided Geometric
Design. A K Peters, 1993.
[14] Howard, T L J, Hewitt, W T, Hubbold, R J, and Wyrwas, K M, APractical
Introduction to PHIGS and PHIGS PLUS. Addison-Wesley, 1991.
[15] Lane, J and Riesenfeld, R, ‘A geometric proof for the variation diminishing
property of B-spline approximation’. J. of Approximation Theory Vol. 37,
pp1–4, 1983.
[16] M¨antyl¨a, M, An Introduction to Solid Modeling, Computer Science Press,
Maryland, 1988.
[17] Munchmeyer, F, ‘On surface imperfections’. In R.Martin, editor, The
Mathematics of Surfaces II, pp459–474. OUP, 1987.
[18] Munchmeyer, F, ‘Shape interrogation: a case study’. In G.Farin, editor,
Geometric Modelling: Algorithms and New Trends, pp291–301. SIAM,
Philadelphia, 1987.
[19] Phong, B-T, ‘Illumination for computer-generated pictures’. Comm. ACM,
Vol. 18, No. 6, pp311–317, June 1975.
[20] Piegl, L and Tiller, W, The NURBS Book. Springer-Verlag, 1995.
[21] Rogers, D F and Adams, J A, Mathematical Elements for Computer
Graphics. Second Edition. McGraw-Hill, 1990.
[22] Schoenberg, I, ‘Contributions to the problem of approximation of equidis-
tant data by analytic functions’, Quart. Appl. Math. Vol. 4, pp45–99, 1946.
[23] Sederberg, Th W, Anderson, D C and Goldman, R N, ‘Implicit represen-
tation of parametric curves and surfaces’. Computer Vision, Graphics and
Image Processing Vol. 28, pp72–84, 1984.
[24] Semple, J G and Kneebone, G T, Algebraic Projective Geometry. OUP,
1952.
[25] Smith, G, Introductory Mathematics: Algebra and Analysis. Springer-
Verlag, 1998.
[26] Sommerville, D M Y, Analytical Conics. Bell and Sons, 1945.
[27] Spivak, M, Calculus. W.A.Benjamin, 1967.
Index
affine invariance 147, 177, 195, 214, 236
ambient light 299, 304
apparent contour 310
apparent cusps 319
attenuation 305
axonometric projection see projection
B-rep 263
B-spline 194
– basis 187, 192
– closed 200, 235
– curve 188
– derivatives 207, 216, 238
– integral 188
– NURBS 212
– open 196, 235
– open uniform 202
– periodic 200, 235
– rational 213
– surface 234
– uniform 198
Bernstein
– polynomial 141, 144
B´ezier
– control point 135
– – homogeneous 175
– control polygon 135–137, 141
– cubic 137
– curve 136, 141, 161
– – curvature 283
– – torsion 283
– derivatives 162
– endpoint-interpolation 139, 147, 236
– integral 141
– linear 136
– piecewise 168
– properties 147
– quadratic 136
– rational 175
– rendering 157
– subdivision 154
– surface 234
binomial 142
blend 233
Boehm algorithm 221
breakpoints 169, 192
C
k
-continuity 99, 170, 226
CAD see computer-aided design, 260
Cartesian plane 2
catenary 273
cavalier projection see projection
centre of perspectivity 68
clip 76
clothoid 273
CMY 299
computer-aided design 49, 135
concatenation see transformation
conic 109
– applications 132
– central 113
– conversion 127
– degenerate 109
– directrix 110
– discriminant 112
– eccentricity 110
– ellipse 109, 116, 177
– focus 110
– hyperbola 109, 116, 134, 177
– irreducible 112, 114
347
348 Index
– parabola 109, 116, 132, 177
– parametrization 124
– reducible 112, 114
– spatial 130
continuity 99, 192, 195, 214, 226, 253
control point 187
conversion
–toB´ezier form 166
convex hull 146, 147, 177, 195, 214, 236
Coons surface 256
coordinate
– functions 96
coordinate curve 226
coordinates
– Cartesian 1
– homogeneous 14, 20, 41
–Pl¨ucker 54
– viewplane see viewplane
Cornu spiral 273
CSG 261
curvature 267, 275
–B´ezier curves 283
– normal 286
– principal 286
– vector 275
curve
– algebraic 96
– curvature 267, 275
– implicit 96
– non-parametric explicit 96
– parametric 96
– polynomial 96
– rational 96
– regular 99
–segment 96
cusp 138
cycloid 273
de Boor algorithm 205
– rational 218
de Casteljau 151, 152
– rational 180
deformation 204
degree 96, 187
degree raising 146
Denavit–Hartenberg 17
device coordinate transformation 37,
80
device window 76
diffuse reflection 300
dimetric projection see projection
dual 40
elliptic point 291
equivalence relation 21
Euler angles 51
Euler–Poincar´e formula 265
evolute 274
flat point 291
flat shading 307
font design 203
foreshortening ratio 85
Frenet frame 276
Frenet–Serret formulae 277
G
k
-continuity 172, 253
geometric continuity 172
geometric modelling 260
gimbal lock 51, 64
Gordon–Coons surface 256
Gouraud shading 307
graphical primitive 1, 15
Hamilton 56
helix 279
Hermite 254
hidden line 318
homogeneous
– control point 213
– coordinates 19, 21
– equation 24, 38
Horner’s method 98
hotspot 303
HSV 298
hue 298
hyperbolic point 291
identity see transformation
image 3
implicit 2, 225
incident ray 300
inflection 138
instancing 1, 15, 36
intensity 301, 305
intersection
– line and B´ezier curve 158
– line and conic 121
– three planes 53
–twoB´ezier curves 159
– two lines 39
inverse see transformation
isometric projection see projection
knot insertion 221
knot vector 187
Lambert’s Law 301
Index 349
Lambertian surfaces 301
light
– ambient 299
– attenuation 305
– directional 299
– distributive 299
– intensity 301
– point source 299
– specular 299
line 2
– through two points 39
line coordinates 54
line vector 39, 52
local control 195, 214
local support 192
lofting 254
logarithmic spiral 273
Monge patch 227
monomial form 166
morphing 203
natural equation 272
normal
– line 101
– vector 100
normal plane 276
numerically controlled machining 107,
232
NURBS see B-spline
object 4
oblique projection see projection
offset 107, 232, 296
order 187
orientation 50
orthogonal change of coordinates 33
orthographic projection see projection
P
3
see projective space
parabolic point 291
parallel curve 107
parallel projection see projection
parameter curve 226
parametric 2, 226
parametrization 96
partition of unity 192
perspective projection see projection
Phong 303, 309
picture elements 15
piecewise polynomial 170, 187, 192
plane
– Cartesian 2
– projective 19, 23, 24
– through three points 52
plane vector 52
point at infinity 23, 25, 26, 41
positivity 192
principal curvature 286
principal direction 286
projection
– centre of perspectivity 72
– line 68
–ofB´ezier curve 181
– of NURBS curve 214
– parallel 69, 72
– – axonometric 86
– – cavalier 88
– – dimetric 87
– – isometric 87
– – oblique 87
– – orthographic 86
– – trimetric 87
– perspective 68, 72, 90
– – one-point 91
– – three-point 91
– – two-point 91
– viewpoint 72
projective invariance 178, 236
projective plane 19, 23, 24
P
2
see projective plane
projective space 41
quaternions 51, 56
– algebraic properties 58
– animation 65
– conjugate 59
– interpolation 65
–inverse 59
– polar form 60
– rotations 62
– unit 59
R
2
see Cartesian plane
rational 175, 213
rectifying plane 276
reflected ray 300
reflection see transformation
– ambient 304
– diffuse 300
– specular 302
regular 99, 226
relation 21
rendering 98
reparametrization 104
RGB 298
right inverse 77
robotics 17