function [SD1, SD2, SD1_SD2_ratio] = EvalPoincareOnWindows(rr, rri, HRVparams, WinStarIdxs, sqi)
% OVERVIEW:
% Calculates SD1 SD2 and SD1_SD2_ratio features from Poincare plot
% for each defined windows
% INPUT
% rr - rr intervals
% rri - index of rr intervals
% HRVparams - struct of settings for hrv_toolbox analysis
% sqi - Signal Quality Index; Requires a matrix with
% at least two columns. Column 1 should be
% timestamps of each sqi measure, and Column 2
% should be SQI on a scale from 0 to 1.
% WinStarIdxs - Starting index of each windows to analyze
%
% OUTPUTS:
% SD1 : (ms) standard deviation of projection of the
% PP on the line perpendicular to the line of
% identity (y=-x)
% SD2 : (ms) standard deviation of the projection of the PP
% on the line of identity (y=x)
% SD1_SD2_ratio : (ms) SD1/SD2 ratio
%
%
% Written by: Giulia Da Poian <giulia.dap@gmail.com>
% REPO:
% https://github.com/cliffordlab/PhysioNet-Cardiovascular-Signal-Toolbox
% COPYRIGHT (C) 2016
% LICENSE:
% This software is offered freely and without warranty under
% the GNU (v3 or later) public license. See license file for
% more information
%
% Make vector a column
rr = rr(:);
if nargin < 4
error('no data provided')
end
if nargin <5 || isempty(sqi)
sqi(:,1) = rri;
sqi(:,2) = ones(length(rri),1);
end
windowlength = HRVparams.windowlength;
SQI_th = HRVparams.sqi.LowQualityThreshold; % SQI threshold
WinQuality_th = HRVparams.RejectionThreshold; % Low quality windows threshold
% Preallocation (all NaN)
SD1 = ones(length(WinStarIdxs),1)*NaN;
SD2 = ones(length(WinStarIdxs),1)*NaN;
SD1_SD2_ratio = ones(length(WinStarIdxs),1)*NaN;
% Run PoincareMetrics by Windows
% Loop through each window of RR data
for i_win = 1:length(WinStarIdxs)
if ~isnan(WinStarIdxs(i_win))
% Isolate data in this window
sqi_win = sqi( sqi(:,1) >= WinStarIdxs(i_win) & sqi(:,1) < WinStarIdxs(i_win) + windowlength,:);
nn_win = rr( rri >= WinStarIdxs(i_win) & rri < WinStarIdxs(i_win) + windowlength );
lowqual_idx = find(sqi_win(:,2) < SQI_th); % Analysis of SQI for the window
% If enough data has an adequate SQI, perform the calculations
if numel(lowqual_idx)/length(sqi_win(:,2)) < WinQuality_th
[SD1(i_win), SD2(i_win), SD1_SD2_ratio(i_win)] = PoincareMetrics(nn_win);
end % end of conditional statements run when SQI is adequate
end % end of check for sufficient data
end % end of loop through windows
end % end of function