20190510_01

coordinates = Get@"https://pastebin.com/raw/0t1MBAgX";

scaleX = 1.418*10^-2;
scaleZ = 1.425*10^-2;

{lX, lZ} = {1600, 1200};

kX = 2*Pi/(lX*scaleX)*(Range[lX] - lX/2) // N;
kZ = 2*Pi/(lZ*scaleZ)*(Range[lZ] - lZ/2) // N;

cx = Flatten[coordinates[[All, 1]]];
cy = Flatten[coordinates[[All, 2]]];

rX = Flatten@Outer[Differences[{##}] &, cx, cx];
rZ = Flatten@Outer[Differences[{##}] &, cy, cy];

nP = Length[coordinates];

s = Array[0 &, {lZ, lX}];

Do[
   Do[
    s[[j, i]] = 1/nP*Total[Cos[kX[[i]]*rX + kZ[[j]]*rZ]]
    , {i, 1, lX}
    ]
   , {j, 1, lZ}
   ]; // AbsoluteTiming