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AN ENGINEER’S GUIDE TO MATLAB 3rd Edition CHAPTER 7 3D GRAPHICS. Chapter 7 – Objective Present the implementation of a wide selection of three-dimensional plotting capabilities. Topics. Lines in 3D Surfaces. Lines in 3D - The 3D version of plot is

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3rd Edition

CHAPTER 7

3D GRAPHICS

• Chapter 7 – Objective

• Present the implementation of a wide selection of three-dimensional plotting capabilities.

Lines in 3D

Surfaces

• Lines in 3D -

• The 3D version of plot is

• plot3(u1, v1, w1, c1, u2, v2, w2, c2,…)

• where

• uj, vj, and wj are the x, y, and z coordinates, respectively, of a point.

• They are scalars, vectors of the same length, matrices of the same order, or expressions that, when evaluated, result in one of these three quantities.

• cj is a string of characters -

• One character specifies the color.

• One character specifies the point characteristics.

• One or two characters specify the line type.

• To draw a set of n unconnected lines whose end points are

• (x1j,y1j,z1j) and (x2j,y2j,z2j), j = 1, 2, …, n

• we create six vectors

• Then, plot3 is

• x1 = […]; x2 = […];

• y1 = […]; y2 = […];

• z1 = […]; z2 = […];

• plot3([x1; x2], [y1; y2], [z1; z2])

• where [x1; x2], [y1; y2], and [z1; z2] are each (2n) matrices.

• Example – Drawing Wire Frame Boxes applicable to the 3D curve- and surface-generating functions, except that the arguments of

• We shall create a function called BoxPlot3 to draw the four edges of each of the six surfaces of a box and then use the function to draw several boxes.

The location and orientation of the box are determined by the coordinates of its two diagonally opposed corners: P(xo,yo,zo) and P(xo+Lx, yo+Ly, zo+Lz).

The script is

f the coordinates of its two diagonally opposed corners: P(unction BoxPlot3(x0, y0, z0, Lx, Ly, Lz)

x = [x0, x0, x0, x0, x0+Lx, x0+Lx, x0+Lx, x0+Lx]; %(18)

y = [y0, y0, y0+Ly, y0+Ly, y0, y0, y0+Ly, y0+Ly]; %(18)

z = [z0, z0+Lz, z0+Lz, z0, z0, z0+Lz, z0+Lz, z0]; %(18)

index = zeros(6,5);

index(1,:) = [1 2 3 4 1];

index(2,:) = [5 6 7 8 5];

index(3,:) = [1 2 6 5 1];

index(4,:) = [4 3 7 8 4];

index(5,:) = [2 6 7 3 2];

index(6,:) = [1 5 8 4 1];

for k = 1:6

plot3(x(index(k,:)), y(index(k,:)), z(index(k,:)))

hold on

end

• Box #1

• Size: 357

• Location: (1,1,1)

• Box #2

• Size: 451

• Location: (3,4,5)

• Box #3

• Size: 111

• Location: (4.5,5.5,6)

function BoxPlot3(x0, y0, z0, Lx, Ly, Lz)

If we assume that a = 10.0, b = 1.0, c = 0.3, and 0 t 2, then the script is

t = following dimensions and the coordinates (linspace(0, 2*pi, 200);

a = 10; b = 1.0; c = 0.3;

x = b*cos(t);

y = b*sin(t);

z = c*cos(a*t);

plot3(x, y, z, 'k')

axis equal

• Surfaces following dimensions and the coordinates (

• A set of 3D plotting functions is available to create surfaces, contours, and variations and specialization of these basic forms.

• A surface is defined by the expression

where x and y are the coordinates in the xy-plane and z is the resulting height.

• The basic surface plotting functions are following dimensions and the coordinates (

• surf(x, y, z)

• and

• mesh(x, y, z)

• where the x, y, and z are the coordinates of the points on the surface.

• surf – draws a surface composed of colored patches.

• The colors of the patches are determined by the magnitude of z.

• mesh – draws white surface patches that are defined by

• their boundary.

• The colors of the lines are determined by the magnitude of z.

• Example following dimensions and the coordinates ( –

• Consider the surface created by

over the range 3 < x < 3 and 3 < y < 13.

We shall place the generation of the x, y, and z coordinate values in an M file so that we can use it in several examples.

We call this function SurfExample.

function following dimensions and the coordinates ( [x, y, z] = SurfExample

x1 = linspace(-3, 3, 15); % (115)

y1 = linspace(-3, 13, 17); % (117)

[x, y] = meshgrid(x1, y1); % (1715)

z = x.^4+3*x.^22*x+6-2*y.*x.^2+y.^2-2*y; % (1715)

Difference Between following dimensions and the coordinates (surf and mesh

[x,y,z] = SurfExample;

surf(x, y, z)

[x,y,z] = SurfExample;

mesh(x, y, z)

[x,y,z] = SurfExample; following dimensions and the coordinates (

mesh(x, y, z)

hidden off

• Combining Surfaces and Lines following dimensions and the coordinates (

• One can combine 3D plotting functions to draw multiple surfaces and multiple lines.

• To illustrate this, we create two functions –

• Corners

• Draws four lines connecting the corners of the surface generated by SurfExample to the xy-plane passing through z = 0.

• Disc

• Creates a circular disc that intersects the surface created by SurfExample at zo = 80, has a radius of 10 units, and has its center at (0,5).

The coordinates of the corners are: following dimensions and the coordinates (

(3, 3, z(3,3))

(3, 13, z(3,13))

(3, 3, z(3,3))

(3, 13, z(3,13))

• The two functions are

• function Corners

• xc = [-3, -3, 3, 3];

• yc = [-3, 13, 13, -3];

• zc = xc.^4+3*xc.^22*xc+62*yc.*xc.^2+yc.^22*yc;

• hold on

• plot3([xc; xc], [yc; yc], [zeros(1,4); zc], 'k')

function following dimensions and the coordinates ( Disc(R, zo)

r = linspace(0, R, 12); % (112)

theta = linspace(0, 2*pi, 50); % (150)

x = cos(theta')*r; % (5012)

y = 5 + sin(theta')*r; % (5012)

hold on

z = repmat(zo, size(x)); % (5012)

surf(x, y, z)

• The script is following dimensions and the coordinates (

• [x, y, z] = SurfExample;

• surf(x, y, z);

• Disc(10, 80)

• Corners

• Altering Graph Appearance following dimensions and the coordinates (

• Several functions that can be used in various combinations to alter the appearance of the resulting surface plot are -

• box on or box off

• grid on or grid off

• axis on or axis off

• The function boxon only draws a box if axison has been selected.

Illustration of following dimensions and the coordinates (box, grid, and axis

[x,y,z] = SurfExample

mesh(x, y, z)

grid off

[x,y,z] = SurfExample

mesh(x, y, z)

axis off

grid off

[x,y,z] = SurfExample following dimensions and the coordinates (

mesh(x, y, z)

axis on

grid off

box on

• The colors of either the patches created by surf or the lines created by mesh can be changed to a uniform color using

• colormap(c)

• where c is a three-element vector, each of whose value varies between 0 and 1.

• The first element corresponds to the intensity of red, the second to the intensity of green, and the third to the intensity of blue.

Some Values of the Color Vector Used in lines created by mesh can be changed to a uniform color usingcolormap(c)

Additional Ways to Visually Enhance a Surface lines created by mesh can be changed to a uniform color using

[x,y,z] = SurfExample;

meshz(x, y, z)

[x,y,z] = SurfExample;

waterfall(x, y, z)

[x,y,z] = SurfExample; lines created by mesh can be changed to a uniform color using

ribbon(y, z)

[x,y,z] = SurfExample;

surfnorm(x, y, z)

• Contour Plots lines created by mesh can be changed to a uniform color using

• Surfaces can also be transformed into contour plots, which are plots of the curves formed by the intersection of the surface and a plane parallel to the xy-plane at given values of z.

• The functions

• surfc(x, y, z)

• meshc(x, y, z)

• create surfaces with contours projected beneath the surface.

• The quantities x, y, and z are the values of the coordinates of points that define the surface.

Illustration of lines created by mesh can be changed to a uniform color usingmeshc and surfc

[x,y,z] = SurfExample;

meshc(x, y, z)

grid off

[x,y,z] = SurfExample;

surfc(x, y, z)

grid off

• Various contour plots without the surfaces can be created, either with labels or without labels.

• The function

• contour(x, y, z, v)

• creates a 2D contour plot where

• x, y, and z are the coordinates of the points that define the surface.

• v, if a scalar, is the number of contours to be displayed and, if a vector of values, the contours of the surface at those values of z .

• The use of v is optional.

Illustration of following pair of functions.contour and clabel

[x,y,z] = SurfExample;

contour(x, y, z)

[x,y,z] = SurfExample;

contour(x, y, z, 4)

[x,y,z] = SurfExample; following pair of functions.

[C, h] = contour(x, y, z);

clabel(C, h)

[x,y,z] = SurfExample;

v= [10, 30:30:120];

[clabel(C, h, v)

• To display the contours of the surface in 3D, we use following pair of functions.

• contour3(x, y, z, v)

• where

• x, y, and z are the coordinates of points that define the surface.

• v, if a scalar, is the number of contours to be displayed and, if a vector of values, the contours of the surface at those values of z.

• The use of v is optional.

• To label the contour plot, we use the pair of functions

• [C, h] = contour3(x, y, z, v)

• clabel(C, h, v)

• To fill the region between the 2D contours with different colors, we use

• contourf(x, y, z, v)

• The values of the colors can be identified using

• colorbar(s)

• which places a bar of colors and their corresponding numerical values adjacent to the figure.

• The quantity s is a string equal to either 'horiz' or 'vert' to indicate the orientation of the bar.

• The default value is 'vert'.

Illustration of colors, we usecontour3, contourf, and colorbar

[x,y,z] = SurfExample;

[C, h] = contour3(x, y, z);

clabel(C, h)

[x,y,z] = SurfExample;

[C, h] = contourf(x, y, z);

colorbar

• The properties of the lines and numbering in contour can be altered a similar manner that was done for plot. For example, to have the contour labels created by contour be enlarged to 14 points and for all the contour lines to be blue, we employ the following steps.

• [x, y, z] = SurfExample;

• [C, h] = contour(x, y, z, v)

• g = clabel(C, h, v);

• set(g, 'Fontsize', 14)

• set(h, 'LineColor', ‘b')

• Generation of Cylindrical, Spherical, and Ellipsoidal Surfaces

• One can use a 2D curve as a generator to create surfaces of revolution by using

• [x, y, z] = cylinder(r, n)

• which returns the x, y, and z coordinates of a cylindrical surface using the vector r to define a profile curve.

• The function cylinder treats each element in r as a radius at n equally spaced points around its circumference.

• If n is omitted, a value of 20 is used.

• Example Surfaces –

• Consider the curve

• which is rotated 360 about the z-axis.

• Let us take 26 equally spaced increments in the z-direction and 16 equally spaced increments in the circumferential direction.

• The script to plot a cylindrical surface is

• zz = linspace(0, 2*pi, 26);

• [x, y, z] = cylinder(1.1+sin(zz), 16);

• surf(x, y, z)

• axis off

• To create a Surfacessphere, one can use

• [x, y, z] = sphere(n);

• axisequal

• surf(x, y, z)

• where n is the number of n by n elements that will comprise the sphere of radius 1 centered at the origin.

• If n is omitted, then n = 20.

• To create an Surfacesellipsoid, we use

• [x, y, z] = ellipsoid(xc, yc, zc, xr, yr, zr, n);

• axisequal

• surf(x, y, z)

• which is centered at (xc, yc, zc) and has semi-axis lengths in the x, y, and z directions, respectively, of xr, yr, and zr.

• In addition, n is the number of n by n elements that will comprise the ellipsoid.

• If n is omitted, then n = 20.

• Viewing Angle Surfaces

• There are instances when one wants to change the default viewing angle of the 3D image because –

• It does not display the features of interest.

• Several different views are to be displayed using subplot.

• Exploration of the surface from many different views is desired before deciding on the final orientation.

• To determine the azimuth and elevation angle of the view, we use

• [a, e] = view

• where a is the azimuth and e the elevation.

• To orient the object, one depresses the SurfacesRotate 3D icon in the figure window and orients the object until a satisfactory orientation is obtained.

• Upon typing the previous expression in the command window, the values of the azimuth and elevation will be displayed.

• These values are recorded and entered in the expression

• view(an, en)

• to create the desired orientation the next time that the script is executed.

• In this expression, an and en are the numerical values of a and e taken from the command window.

• The surfaces created with surf have used the default shading property called 'faceted'.

• The function that changes the shading is

• where s is a string equal to

• faceted% Default

• flat

• interp

zz = linspace(0, 2*pi, 26);

r=1.1+sin(zz);

[x, y, z] = cylinder(r, 16);

surf(x, y, z)

view(-88.5, -48)

axis off vis3d

• zz = Surfaceslinspace(0, 2*pi, 26);

• r=1.1+sin(zz);

• [x, y, z] = cylinder(r, 16);

• surf(x, y, z)

• view(-88.5, -48)

• axis off vis3d

zz = Surfaceslinspace(0, 2*pi, 26);

r=1.1+sin(zz);

[x, y, z] =cylinder(r, 16);

surf(x, y, z)

view(-88.5, -48)

axis off vis3d

r = 1+ Surfacessin(zz);

[x, y, z] = cylinder(r, 16);

surf(x, y, z)

view(-88.5, -48)

colormap(copper)

axis offvis3d

• Transparency Surfaces

• The surfaces created with surf can have their opaqueness altered using set and assigning a numerical value to the keyword 'FaceAlpha'.

• The effect of this keyword on the resulting surface is dependent on the type of shading chosen.

• To illustrate the use of this transparency option, we create a function that generates the numerical values for the surface given by

• If we assume that Surfacesa = 1.13 and b = 1.14, then the function M file for this surface is

• function [x, y, z] = Transparency

• a = 1.13; b = 1.14;

• uu = linspace(0, 2*pi, 30);

• vv = linspace(-15, 6, 45);

• [u, v] = meshgrid(uu, vv);

• x = a.^v.*cos(v).*(1+cos(u));

• y = -a.^v.*sin(v).*(1+cos(u));

• z = -b*a.^v.*(1+sin(u));

[x, y, z] = Transparency; Surfaces

surf(x, y, z)

axisvis3doffequal

view([-35 38])

[x, y, z] = Transparency;

h = surf(x, y, z)

set(h, 'FaceAlpha', 0.4)

axisvis3doffequal

view([-35 38])

[x, y, z] = Transparency; Surfaces

h = surf(x, y, z)

set(h, 'FaceAlpha', 0.4)

axisvis3doffequal

view([-35 38])

• Example - Drawing Wire Frame Boxes: Coloring the Box Surfaces

• We modify the M file BoxPlot3 so that all of the six surfaces represented by the rectangles are each filled with a different color.

• This modification entails using fill3.

• The revised BoxPlot3 is renamed BoxPlot3C and becomes

function Surfaces BoxPlot3C(xo, yo, zo, Lx, Ly, Lz, w)

% w = 0, wire frame; w = 1, rectangles are colored

x = [xo xo xo xo xo+Lx xo+Lx xo+Lx xo+Lx];

y = [yo yo yo+Ly yo+Ly yo yo yo+Ly yo+Ly];

z = [zo zo+Lz zo+Lz zo zo zo+Lz zo+Lz zo ];

index = zeros(6,5);

index(1,:) = [1 2 3 4 1];

index(2,:) = [5 6 7 8 5];

index(3,:) = [1 2 6 5 1];

index(4,:) = [4 3 7 8 4];

index(5,:) = [2 6 7 3 2];

index(6,:) = [1 5 8 4 1];

c = 'rgbcmy';

for k = 1:6

if w~=0

fill3(x(index(k,:)), y(index(k,:)), z(index(k,:)), c(k))

else

plot3(x(index(k,:)), y(index(k,:)), z(index(k,:)))

end

holdon

end

BoxPlot3C(1, 1, 1, 3, 5, 7, 1) Surfaces

BoxPlot3C(4, 6, 8, 4, 5, 1, 0)

BoxPlot3C(8, 11, 9, 1, 1, 1, 1)

where 0  4.

• To create a sphere of radius 2 Highlighting of Their Intersectiona, we multiply each of the coordinates from the output of sphere by 2a.

• The coordinates that are output from cylinder must be altered as follows:

• xax + a

• yay

• z 4az 2a

• We assume that a = 1. The script is

a = 1; Highlighting of Their Intersection

[xs, ys, zs] = sphere(30);

surf(2*a*xs, 2*a*ys, 2*a*zs)

hold on

[x, y, z] = cylinder;

surf(a*x+a, a*y, 4*a*z-2*a)

t = linspace(0, 4*pi, 100);

x = a*(1+cos(t));

y = a*sin(t);

z = 2*a*sin(t/2);

plot3(x, y, z, 'y-', 'Linewidth', 2.5);

axisequaloff

view([45, 30])

• Example - Enhancing 2D Graphs with 3D Objects: Highlighting of Their Intersection

• Volume of Sphere and Ellipsoid

• For a sphere of radius a and an ellipsoid with its major axis in the x-direction equal to 2a, minor axis in the y-direction equal to 2b, and minor axis in the z-direction equal to 2c, the ratio of the volume of an ellipsoid to the volume of a sphere is

We create the following program to enhance the understanding of a plot of V as a function b/a for several values of c/a.

b = [0.5, 1]; c = b; Highlighting of Their Intersection

for k = 1:2

plot(b, b*c(k), 'k-')

text(0.75, (b(1)*c(k)+b(2)*c(k))/2-0.02, ['c/a = ' num2str(c(k))])

hold on

end

xlabel('b/a') ylabel('V')

for k = 1:4

switch k

case 1

axes('position', [0.12, 0.2, 0.2, 0.2])

[xs, ys, zs] = ellipsoid(0, 0, 0, 1, b(1), c(1), 20);

mesh(xs, ys, zs)

text(0, 0, 1, ['b/a = ' num2str(b(1)) ' c/a = ' num2str(c(1))])

case 2

axes ('position', [0.1, 0.5, 0.2, 0.2])

[xs, ys, zs] = ellipsoid(0, 0, 0, 1, b(1), c(2), 20);

mesh (xs, ys, zs)

text (0, 0, 1.5, ['b/a = ' num2str(b(1)) ' c/a = ' num2str(c(2))])

case Highlighting of Their Intersection 3

axes ('position', [0.7, 0.65, 0.2, 0.2])

[xs, ys, zs] = ellipsoid(0, 0, 0, 1, b(2), c(2), 20);

mesh (xs, ys, zs)

text (-1.5, 0, 2, ['b/a = ' num2str(b(2)) ' c/a = ' num2str(c(2))])

case 4

axes ('position', [0.7, 0.38, 0.2, 0.2])

[xs, ys, zs] = ellipsoid(0, 0, 0, 1, b(2), c(1), 20);

mesh (xs, ys, zs)

text (-1.5, 0, 1.5, ['b/a = ' num2str(b(2)) ' c/a = ' num2str(c(1))])

end

colormap([0 0 0])

axisequaloff

end

where

There are two parameters that are of interest: Spring1 and Ks.

We shall generate a surface of the lowest natural frequency coefficient 1 as a function of 1 and log10(Ks).

Then we shall use these same natural frequency coefficients to create a contour plot of log10(Ks) versus 1 for several values of 1/.

The program is

function Spring BeamWithSpring

Neta1 = 28; NKs = 21; Kend = 4;

Ks = logspace(0, Kend, NKs);

Om = linspace(0.02, 10, 50);

Omeg = zeros(Neta1, NKs);

eta1 = linspace(0, 1, Neta1);

for et = 1:Neta1

for kss = 1:NKs

D = NFEqnBeamWithKs(Om, Ks(kss), eta1(et));

for k = 2:length(Om)

if D(k)*D(k-1) < 0

Omeg(et, kss) = fzero(@NFEqnBeamWithKs, …

[Om(k-1), Om(k)], [], Ks(kss), eta1(et));

break

end

end

end

end

figure Spring(1)

mesh(eta1, log10(Ks), (Omeg/pi)')

xlabel('\eta_1')

ylabel('log_{10}(K_s)')

zlabel('\Omega_1/\pi')

view([-15,30])

a = axis; a(4) = Kend;

axis(a)

figure(2)

[C, h] = contour(eta1, log10(Ks), (Omeg/pi)');

clabel(C, h)

xlabel('\eta_1')

ylabel('log_{10}(K_s)')

function Spring C = NFEqnBeamWithKs(Om, Ks, eta1)

CA = T(Om*eta1).*(T(Om).*T(Om*(1-eta1))-R(Om).*R(Om*(1-eta1)));

CB = R(Om*eta1).*(T(Om).*R(Om*(1-eta1))-R(Om).*T(Om*(1-eta1)));

C = CA+CB+(R(Om).^2-T(Om).^2)*Om.^3/Ks;

function r = R(x)

r = 0.5*(sinh(x)+sin(x));

function t = T(x)

t = 0.5*(sinh(x)-sin(x));

where Lx, Ly, and Lz are the x, y, and z components of the translation, respectively, and aij, i, j = 1, 2, 3, are the elements of

• The quantities Spring, , and  are the ordered rotation angles (Euler angles) of the coordinate system about the origin –

• then  about the y-axis

• then  about the z-axis

• In general, (x,y,z) can be scalars, vectors of the same length, or matrices of the same order.

• We first create the function SpringEulerAngles.

• function [Xrt, Yrt, Zrt] = EulerAngles(psi, chi, phi, …

• Lx, Ly, Lz, x, y, z)

• a = [cos(psi)*cos(chi), -cos(psi)*sin(chi), sin(psi); …

• cos(phi)*sin(chi)+sin(phi)*sin(psi)*cos(chi), …

• cos(phi)*cos(chi)-sin(phi)*sin(psi)*sin(chi), …

• -sin(phi)*cos(psi); …

• sin(phi)*sin(chi)-cos(phi)*sin(psi)*cos(chi), …

• sin(phi)*cos(chi)+cos(phi)*sin(psi)*sin(chi), …

• cos(phi)*cos(psi)];

• Xrt = a(1,1)*x+a(1,2)*y+a(1,3)*z+Lx;

• Yrt = a(2,1)*x+a(2,2)*y+a(2,3)*z+Ly;

• Zrt = a(3,1)*x+a(3,2)*y+a(3,3)*z+Lz;

• Example Spring –

• We now illustrate the use of these transformation equations with the manipulation of a torus, whose coordinates are given by

where barb + a, 0  2, and b > a.

• We first create the following function to obtain the coordinates of the torus.

• function [X, Y, Z] = Torus(a, b)

• r = linspace(b-a, b+a, 10);

• th = linspace(0, 2*pi, 22);

• x = r'*cos(th);

• y = r'*sin(th);

• z = real(sqrt(a^2-(sqrt(x.^2+y.^2)-b).^2));

• X = [x x];

• Y = [y y];

• Z = [z -z];

• where real is used to eliminate any small imaginary parts caused by numerical round-off.

• We obtain four plots of the torus: coordinates of the torus.

• (1) No rotations.

• (2) Rotated 60 about the x-axis ( = 60) and compared to the orientation of the original torus.

• (3) Rotated 60 about the y-axis ( = 60) and compared to the orientation of the original torus.

• (4) Rotated 60about the x-axis ( = 60), rotated 60 about the y-axis ( = 60) and compared to the orientation of the original torus.

• We assume that a = 0.2 and b = 0.8 and we use colormap to produce a mesh of black lines.

• The script is coordinates of the torus.

• [X, Y, Z] = Torus(0.2, 0.8);

• psi = [0, pi/3, pi/3]; chi = [0, 0, 0]; phi = [pi/3,0, pi/3];

• Lx = 0; Ly = 0; Lz = 0;

• for k = 1:4

• subplot(2,2,k)

• if k==1

• mesh(X, Y, Z)

• else

• mesh(X, Y, Z)

• holdon

• [Xr Yr Zr] = EulerAngles(psi(k-1), chi(k-1), …

• phi(k-1), Lx, Ly, Lz, X, Y, Z);

• mesh(Xr, Yr, Zr)

• end

• switch coordinates of the torus. k

• case 1

• text(0.5, -0.5, 1, 'Torus')

• case 2

• text(0.5, -0.5, 1,'\phi = 60\circ')

• case 3

• text(0.5,-0.5,1,'\psi = 60\circ')

• case 4

• text(0.5, -0.5, 1.35,'\psi = 60\circ')

• text(0.55, -0.5, 1,'\phi = 60\circ')

• end

• colormap([0 0 0])

• axis equal off

• grid off

• end