How to find index of closest value in a column array for every value in another column array.

I have an array called 'loc' that contains longitudes in the first column and latitudes in the second column. Additionally, I have an array called 'lonlat' that contains longitudes in the first column and latitudes in the second column. For every latitude and longitude pair in 'lonlat' I need to find the index of the closest latitude and longitude pair in 'loc'. 'lonlat' and 'loc' both have two columns but they have a different number of rows.

Answer 1

[Jorge Mario Guerra González]

You can adapt this according to your needs.

you just have to use loops to make a serires of comparations. Also you have to know how to messure the the distance using longitude and latitude.

Check if this works.

loc=360*rand(20,2)-180;
lonlat=360*rand(5,2)-180;
closest=zeros(size(lonlat,1),3);
aux=zeros(size(loc,1),1);
R=6373; %Km
for i=1:size(lonlat,1)
    lon2=lonlat(i,1); lat2=lonlat(i,2);
    for j=1:size(loc,1)
        lon1=loc(j,1); lat1=loc(j,2);
        dlon = lon2 - lon1;
        dlat = lat2 - lat1 ;
        a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2;
        c = 2 * atan2( sqrt(a), sqrt(1-a) ) ;
        d = R * c; %where R is the radius of the Earth
        aux(j)=d;
    end
    idx=find(aux==min(aux(:)));
    closest(i,1:2)=loc(idx,:);
    closest(i,3)=aux(idx);
end

I made use some random lons and lats, the algorithm to calculate the distance was taken from this site.

http://andrew.hedges.name/experiments/haversine

closest is the result matrix, which has the closest coordinate from loc for each coordinate lonlat respectively, [lon lat min(distance)]

Hope it works