function [dref] = mcxcwdref(detp, cfg)
%
%  [dref] = mcxcwdref(detp, cfg)
%
%  Compute CW diffuse reflectance from MC detected photon profiles
%
%  author: Shijie Yan (yan.shiji <at> northeastern.edu)
%
%  input:
%    detp: profiles of detected photons
%    cfg:  a struct, or struct array. Each element of cfg defines
%         the parameters associated with a MC simulation.
%
%  output:
%    dref: CW diffuse reflectance at detectors
%
%    this file is part of Monte Carlo eXtreme (MCX)
%    License: GPLv3, see http://mcx.sf.net for details
%    see Yao2018
%
unitinmm = 1;
if (isfield(cfg, 'unitinmm'))
    unitinmm = cfg.unitinmm;
end
detweight = mcxdetweight(detp, cfg.prop);
detnum = length(unique(detp.detid));
detweightsum = zeros(detnum, 1);
for i = 1:length(detp.detid)
    detweightsum(detp.detid(i)) = detweightsum(detp.detid(i)) + detweight(i);
end
area = pi * (cfg.detpos(:, 4) * unitinmm).^2;
dref = detweightsum ./ area / cfg.nphoton; % Eq.12 of photon replay paper[Yao2018]
end