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I have the plot of the borders of the continents. how can i create circles like those in the picture? I have the latitude and longitude of the central point, the radius of the circumference, which would be a distance, and 10 points that would build the circumference that are 36 degrees apart from each other.

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Simon Chan
Simon Chan 2021-8-16
编辑：Simon Chan 2021-8-16

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Use function pol2cart
clear; clc;
separation = 36; % Angle separation
rhoA = 10; % Radius #1, 10 pixels
rhoB = 15; % Radius #2, 15 pixels
num_dot = 360/separation +1; % Total number of points
theta = linspace(-pi,pi,num_dot); % Theta separation
cx = 50; % Your center point, x-coordinates = 50 (example)
cy = 25; % Your center point, y-coordinates = 25 (example)
[xA,yA] = pol2cart(theta,rhoA); % Use pol2cart
[xB,yB] = pol2cart(theta,rhoB); % Use pol2cart
A = zeros(100,100); % Original region, example, size: 100x100
[Ny, Nx]= size(A);
xA_convert = round(cx-xA); % Convert back from polar coordinates
yA_convert = round(cy-yA);
xB_convert = round(cx-xB);
yB_convert = round(cy-yB);
for k = 1:num_dot
A(yA_convert(k),xA_convert(k)) =1; % Put the dots in matrix A (can skip this loop)
A(yB_convert(k),xB_convert(k)) =1;
end
plot(cx,cy,'ro'); % Your center point
hold on
plot(xA_convert,yA_convert,'b+')
plot(xB_convert,yB_convert,'g*')
xlim([0 Nx])
ylim([0 Ny])

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ok thanks now i try :)
it seems to work but how do I convert the radius in pixels to km? in the sense I have the information of the distance in km, I have to enter the pixel from what I understand.
Thanksss
Simon Chan
Simon Chan 2021-8-17
编辑：Simon Chan 2021-8-17
May use this function: latlon2local

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