function c=center(BW)
%computes 2-vector c as centroid of binary image BW
area=sum(sum(BW))+.0000001;
[l1,l2]=size(BW);
[X2,X1]=meshgrid(1:l2,(1:l1)');
c=[0 0];
c(1)=sum(sum(X1.*BW))/area;
c(2)=sum(sum(X2.*BW))/area;