function tellside()
clear all;
a = textread('1.TXT');
x1 = 525056.71;
y1 = 3385799.17;
z1 = 5.84;
x2 = 525144.92;
y2 = 3385446.93;
z2 = 6.42;
v = [x2-x1,y2-y1,1];
for k=1:1000000
vk = [x2 - a(k,1),y2 - a(k,2),1];
%ws = v(1,1) * vk(1,2) - v(1,2) * vk(1,1);
%ws = v.x * vk.y - v.y * vk.x;
ws = cross(v,vk);
if ws < 0
    %a(k,1) = 525144.92;
    %a(k,2) = 3385446.93;
    %a(k,3) = 0;
    %a(k,:) = [];
    a(k,1) = 0;
end
end
%[m,n] = size(a);
%for k=1:m
%    if a(k,1) == 0
%        a(k,:) = [];
%        [m,n] = size(a);
%    end
%end
a = a(find(a(:,1) ~=0.0),:)
dlmwrite('2000000.xyz',a,'delimiter','\t','precision','%.1f') ;