Using Coordinate System in Matlab

Question

I've been working on a project involving inverse source problem known within the electromagnetic wave field. The problem i have is that ; I have to define 3 points in a 2D space. These points should have a x,y coordinate of course and a value which will define its' current. Like this:

A1(2,3)=1
A2(2,-2)=2
and so on.

Also i have to define a circle around this and divide it into 200 points. Like the first point would be ; say R=2 ; B1(2,0) ;B50(0,2);B100(-2,0) and so on.

Now i really am having a hard time to define a space in MATLAB and circle it. So what i am asking is to help me define a 2D space and do it as the way i described. Thanks for any help guys!

Answer 1

This kind of code may be use. Look at grid in the Variable editor.

grid = zeros(50, 50);
R = 10;
angles = (1:200)/2/pi;
x = cos(angles)*R;
y = sin(angles)*R;

center = [25 20];

for n=1:length(angles)   
    grid(center(1)+1+round(x(n)), center(2)+1+round(y(n))) = 1;
end

You have to define a grid large enough for your need.

Answer 2

Here is a complete example that might be of help:

%# points
num = 3;
P = [2 3; 2 -2; -1 1];          %# 2D points coords
R = [2.5 3 3];                  %# radii of circles around points

%# compute circle points
theta = linspace(0,2*pi,20)';   %'
unitCircle = [cos(theta) sin(theta)];
C = zeros(numel(theta),2,num);
for i=1:num
    C(:,:,i) = bsxfun(@plus, R(i).*unitCircle, P(i,:));
end

%# prepare plot
xlims = [-6 6]; ylims = [-6 6];
line([xlims nan 0 0],[0 0 nan ylims], ...
    'LineWidth',2, 'Color',[.2 .2 .2])
axis square, grid on
set(gca, 'XLim',xlims, 'YLim',ylims, ...
    'XTick',xlims(1):xlims(2), 'YTick',xlims(1):xlims(2))
title('Cartesian Coordinate System')
xlabel('x-coords'), ylabel('y-coords')

hold on

%# plot centers
plot(P(:,1), P(:,2), ...
    'LineStyle','none', 'Marker','o', 'Color','m')
str = num2str((1:num)','A%d');    %'
text(P(:,1), P(:,2), , str, ...
    'HorizontalAlignment','left', 'VerticalAlignment','bottom')

%# plot circles
clr = lines(num);
h = zeros(num,1);
for i=1:num
    h(i) = plot(C(:,1,i), C(:,2,i), ...
        'LineStyle','-', 'Marker','.', 'Color',clr(i,:));
end
str = num2str((1:num)','Circle %d');    %'
legend(h, str, 'Location','SW')

hold off