Gather data

clc
close all
clear all

data = single(csvread('SEDAC_POP_2000-01-01_gs_3600x1800.CSV')); %read population data
data(data == 99999)=0; %make sea uninhabited


sin_vector = sin((1:1800)/1800*pi);
A=sum(sin_vector*data);

%%

new_data=single(zeros(1800,3600));
new_data2=single(zeros(1800,3600));
tic
for lat = 1:1800 %loop latitude
    disp(lat/10)

    latrad = pi*lat/1800-pi/2;
    Filter = single(zeros(1800,3600)); %create empty filter matrix
    for lat2 = 1:1800 %loop latitude
        lat2rad = pi*lat2/1800-pi/2;
        delta_lat = lat2rad - latrad;
        x=sin(delta_lat/2)^2;
        y= cos(latrad) * cos(lat2rad);
        q=sin(lat2rad+pi/2);
        for lon2 = 1:3600 %loop longitude
            lon2rad = pi*lon2/1800-pi;
            delta_lon = lon2rad - pi;
            R = 6371;% Earth's radius in km

            d = R * 2 * asin(sqrt(x + y * sin(delta_lon/2)^2));
            if d < 10000
                 Filter(lat2,lon2)=q;
            end
        end
    end

    for lon = 1:3600
        if data(lat,lon) == 0
            new_data(lat,lon)=sum(sum(single(circshift(Filter,[0 lon])).*data));
        else
            new_data2(lat,lon)=sum(sum(single(circshift(Filter,[0 lon])).*data));
        end

    end
    toc
end