Graphics Programs Reference
In-Depth Information
annular region as shown in the diagram
at right. To define such a set of points
we use a polar grid based on radial and
angular coordinates
r
and
θ
. We use the
following limits on these coordinates:
.
3
≤
r
≤
1
π/
4
≤
θ
≤
5
π/
4
These are set up in matlab as follows:
rv = linspace(.3,1,50);
thv = linspace(pi/4,5*pi/4,50);
[r,th] = meshgrid(rv,thv);
where the calls to
linspace
produce vectors of 50 points covering the
intervals. The
x
and
y
points are defined by the following trigonometric
relations:
x = r.*cos(th);
y = r.*sin(th);
Now our semi-annular region is defined. To prove it, let us plot the
points:
plot(x,y,'.')
Again, we can define any
z
matrix we like. Just for fun, we use the peaks
function of the right size and add a linear ramp:
z = peaks(50) + 10*x;
surf(x,y,z)
As we did in the previous example, we check that the
contour
function
works (omitting the labels this time, and upping the number of contours
drawn to 30):
