function [h,l] = readUPC(fname,limit)
% function [h,l] = readUPC(fname,limit)
% opens a UPC format file, reads the header and limit # of data lines
% it returns two structures.  
% The default for limit is 10,000, which takes 90 seconds. 
% You may use Inf to read all points. 

if nargin < 2
    limit = 1e5;
end

if nargout < 2 % save time: don't read points if there is no returning them. 
    limit = 0;
end

fid = fopen(fname);
if fid == -1
    error(['Could not open ' fname])
end

h = readUPChead(fid);

n = min(double(h.numOfPts), limit);
l.gpsTimeOfWeek=zeros(n,1); % The GPS time of week of the point
l.sensorNum=char(zeros(n,2)); % The laser sensor number used for the point
l.julianDay=char(zeros(n,3)); % The day the point was collected
l.flightLine=char(zeros(n,3)); % The flight line number of the point
l.xyz=zeros(n, 3); % The recorded x-coord of the point
l.intensity=zeros(n,1); % The intensity of the point
l.rgb=zeros(n,3); % The red component of the point
l.returnNum=zeros(n,1); % The return number of the point

for i = 1:n
l.gpsTimeOfWeek(i)=fread(fid,1,'double'); % The GPS time of week of the point
l.sensorNum(i,:)=fread(fid,[1 2],'*char'); % The laser sensor number used for the point
l.julianDay(i,:)=fread(fid,[1 3],'*char'); % The day the point was collected
l.flightLine(i,:)=fread(fid,[1 3],'*char'); % The flight line number of the point
l.xyz(i,:)=fread(fid,[1 3],'int'); % The recorded x-coord of the point
l.intensity(i)=fread(fid,1,'uchar'); % The intensity of the point
l.rgb(i,:)=fread(fid,[1 3],'ushort'); % The red component of the point
l.returnNum(i)=fread(fid,1,'*char'); % The return number of the point
end
fclose(fid);