function id=get_id(zin)
% id=get_id(zin) returns the drifter ids in zin.
% 4/7/01

% remove any initial nans
nnan=find(isnan(zin(:,1)));
zin(nnan,:)=[];
% find drifter id numbers
zin=[zin;1000*ones(1,8)];
nid=find(diff(zin(:,8))>0.01);
id=zin(nid,8);
