3D plot –
Part 3
Continuing
with our 3D graphs, we'll demonstrate the use of the function 'sphere'. We are
going to draw a unit sphere centered at the origin and generated by
matrices x,
y
and z,
of size 31 x 31 each.
Just as an exercise, we also add
a straight line going from the center of the
sphere to one of the corners in the figure (within the same 3D plot). This
is important to note the fact that we can add several shapes
to the figure,
by using the instruction ' hold
on '. We'll
also use functions to label the plot and will see how we can use
two coordinates to find more elements of the line containing
them.
Example:
We plot a transparent
sphere
using appropriate commands. We add a line from the center of the sphere
to one corner of the containing box. We demonstrate the use of
the
instruction 'axis'
with the parameter 'square'.
% cleans the
workspace
clc; clear; close all
% returns the
coordinates of a sphere in three
% matrices
that are (n+1)by(n+1) in size
[x, y, z] = sphere(30);
plot3(x,y,z)
% keeps the
proportions in place and writes appropriate info.
axis('square')
title('Transparent Sphere')
xlabel('x axis')
ylabel('y axis')
zlabel('z axis')
% keeps the
above sphere in order to superimpose a line
hold on
% the line
goes from (1, 1, 1) to (0, 0, 0)
a = 1 : .1 : 0;
b = 1 : .1 : 0;
c = b;
plot3(a, b, c)
% draws the
sphere in another format and in another figure
% see what
happens if we don't use the axis('square') instruction
figure
mesh(x,y,z)
hold on
plot3(a, b, c)
And the resulting figures are:

