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Anton Vernytsky on 8 Mar 2022
Commented: Mathieu NOE on 16 Mar 2022
Open in MATLAB Online
Hello,
i would like to write a code that will calculte the middle of the "bell'.For example y=1 it is the base off the "bell" and the local min point is the top of the "bell" and i need to find the middle of that "bell'' and draw a horizontal line.For example the base is y=1 and the top is y=0.9 so the middle will be line at y=0.95.
This is my code and example of what i want do draw(The red lines).
Thank you.
clear all;
clc;
xlsdata=xlsread('ForDataMining.xlsx');
Wavelength=xlsdata(2:2152);
for i=1:2
reflection = xlsdata(2:2152,i+1);
lmin = islocalmin(reflection,"MinSeparation",100);
bellheight=1-lmin;
bellmid=1-bellheight/2;
plot(Wavelength,reflection,Wavelength(lmin),reflection(lmin),'ro')
hold on
yline(bellmid);
hold off
title('Relative Reflectance-Wavelength')
xlabel('Wavelength[nm]')
ylabel('Relative Reflectance')
grid on
grid minor
figure(i)
end
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Answers (1)
Mathieu NOE on 8 Mar 2022
Open in MATLAB Online
hello Anton
I created some dummy data - as you didn't provide the excel file
here my suggestion, for one local minimum
clear all;
clc;
% some dummy data
Wavelength=1:1000;
reflection = min(ones(size(Wavelength)),1+0.37*sin(Wavelength/150+1.5));
lmin = islocalmin(reflection,"MinSeparation",100);
lmin_value = reflection(lmin);
bellheight=1-lmin_value;
bellmid=1-bellheight/2;
threshold = bellmid; %
[t0_pos,s0_pos,t0_neg,s0_neg]= crossing_V7(reflection,Wavelength,threshold,'linear'); % positive (pos) and negative (neg) slope crossing points
% ind => time index (samples)
% t0 => corresponding time (x) values
% s0 => corresponding function (y) values , obviously they must be equal to "threshold"
x_line = [t0_neg t0_pos];
y_line = threshold*ones(size(x_line));
figure(1)
plot(Wavelength,reflection,Wavelength(lmin),lmin_value,'ro',x_line,y_line,'r',t0_pos,s0_pos,'db',t0_neg,s0_neg,'dg','linewidth',2,'markersize',12);grid on
legend('signal','local min','threshold','positive slope crossing points','negative slope crossing points');
title('Relative Reflectance-Wavelength')
xlabel('Wavelength[nm]')
ylabel('Relative Reflectance')
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [t0_pos,s0_pos,t0_neg,s0_neg] = crossing_V7(S,t,level,imeth)
% [ind,t0,s0,t0close,s0close] = crossing_V6(S,t,level,imeth,slope_sign) % older format
% CROSSING find the crossings of a given level of a signal
% ind = CROSSING(S) returns an index vector ind, the signal
% S crosses zero at ind or at between ind and ind+1
% [ind,t0] = CROSSING(S,t) additionally returns a time
% vector t0 of the zero crossings of the signal S. The crossing
% times are linearly interpolated between the given times t
% [ind,t0] = CROSSING(S,t,level) returns the crossings of the
% given level instead of the zero crossings
% ind = CROSSING(S,[],level) as above but without time interpolation
% [ind,t0] = CROSSING(S,t,level,par) allows additional parameters
% par = {'none'|'linear'}.
%With interpolation turned off (par = 'none') this function always
%returns the value left of the zero (the data point thats nearest
% to the zero AND smaller than the zero crossing).
%
% check the number of input arguments
error(nargchk(1,4,nargin));
% check the time vector input for consistency
if nargin < 2 | isempty(t)
% if no time vector is given, use the index vector as time
t = 1:length(S);
elseif length(t) ~= length(S)
% if S and t are not of the same length, throw an error
error('t and S must be of identical length!');
end
% check the level input
if nargin < 3
% set standard value 0, if level is not given
level = 0;
end
% check interpolation method input
if nargin < 4
imeth = 'linear';
end
% make row vectors
t = t(:)';
S = S(:)';
% always search for zeros. So if we want the crossing of
% any other threshold value "level", we subtract it from
% the values and search for zeros.
S = S - level;
% first look for exact zeros
ind0 = find( S == 0 );
% then look for zero crossings between data points
S1 = S(1:end-1) .* S(2:end);
ind1 = find( S1 < 0 );
% bring exact zeros and "in-between" zeros together
ind = sort([ind0 ind1]);
% and pick the associated time values
t0 = t(ind);
s0 = S(ind);
if ~isempty(ind)
if strcmp(imeth,'linear')
% linear interpolation of crossing
for ii=1:length(t0)
%if abs(S(ind(ii))) >= eps(S(ind(ii))) % MATLAB V7 et +
if abs(S(ind(ii))) >= eps*abs(S(ind(ii))) % MATLAB V6 et - EPS * ABS(X)
% interpolate only when data point is not already zero
NUM = (t(ind(ii)+1) - t(ind(ii)));
DEN = (S(ind(ii)+1) - S(ind(ii)));
slope = NUM / DEN;
slope_sign(ii) = sign(slope);
t0(ii) = t0(ii) - S(ind(ii)) * slope;
s0(ii) = level;
end
end
end
% extract the positive slope crossing points
ind_pos = find(sign(slope_sign)>0);
t0_pos = t0(ind_pos);
s0_pos = s0(ind_pos);
% extract the negative slope crossing points
ind_neg = find(sign(slope_sign)<0);
t0_neg = t0(ind_neg);
s0_neg = s0(ind_neg);
else
% empty output
ind_pos = [];
t0_pos = [];
s0_pos = [];
% extract the negative slope crossing points
ind_neg = [];
t0_neg = [];
s0_neg = [];
end
end
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Mathieu NOE on 8 Mar 2022
Direct link to this comment
https://www-ah.mathworks.com/matlabcentral/answers/1666184-extract-data-from-figure#comment_2027014
Open in MATLAB Online
and now the multiple local minima code :
clear all;
clc;
close all
% some dummy data
Wavelength=1:1000;
reflection = min(ones(size(Wavelength)),1+0.55*sin(Wavelength/330).*sin(Wavelength/50+1.5));
lmin = islocalmin(reflection,"MinSeparation",100);
lmin_index = find(lmin);
lmin_value = reflection(lmin);
plot(Wavelength,reflection,Wavelength(lmin),lmin_value,'ro');
hold on
title('Relative Reflectance-Wavelength')
xlabel('Wavelength[nm]')
ylabel('Relative Reflectance')
for ci = 1:numel(lmin_value)
bellheight=1-lmin_value(ci);
bellmid=1-bellheight/2;
threshold = bellmid; %
[t0_pos,s0_pos,t0_neg,s0_neg]= crossing_V7(reflection,Wavelength,threshold,'linear'); % positive (pos) and negative (neg) slope crossing points
% ind => time index (samples)
% t0 => corresponding time (x) values
% s0 => corresponding function (y) values , obviously they must be equal to "threshold"
% keep closest t0_neg t0_pos values from lmin_value
[val,indd] = min(abs(lmin_index(ci)-t0_neg));
t0_neg_selected = t0_neg(indd);
[val,indd] = min(abs(lmin_index(ci)-t0_pos));
t0_pos_selected = t0_pos(indd);
x_line = [t0_neg_selected t0_pos_selected];
y_line = threshold*ones(size(x_line));
plot(x_line,y_line,'r','linewidth',2,'markersize',12);grid on
end
hold off
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
function [t0_pos,s0_pos,t0_neg,s0_neg] = crossing_V7(S,t,level,imeth)
% [ind,t0,s0,t0close,s0close] = crossing_V6(S,t,level,imeth,slope_sign) % older format
% CROSSING find the crossings of a given level of a signal
% ind = CROSSING(S) returns an index vector ind, the signal
% S crosses zero at ind or at between ind and ind+1
% [ind,t0] = CROSSING(S,t) additionally returns a time
% vector t0 of the zero crossings of the signal S. The crossing
% times are linearly interpolated between the given times t
% [ind,t0] = CROSSING(S,t,level) returns the crossings of the
% given level instead of the zero crossings
% ind = CROSSING(S,[],level) as above but without time interpolation
% [ind,t0] = CROSSING(S,t,level,par) allows additional parameters
% par = {'none'|'linear'}.
%With interpolation turned off (par = 'none') this function always
%returns the value left of the zero (the data point thats nearest
% to the zero AND smaller than the zero crossing).
%
% check the number of input arguments
error(nargchk(1,4,nargin));
% check the time vector input for consistency
if nargin < 2 | isempty(t)
% if no time vector is given, use the index vector as time
t = 1:length(S);
elseif length(t) ~= length(S)
% if S and t are not of the same length, throw an error
error('t and S must be of identical length!');
end
% check the level input
if nargin < 3
% set standard value 0, if level is not given
level = 0;
end
% check interpolation method input
if nargin < 4
imeth = 'linear';
end
% make row vectors
t = t(:)';
S = S(:)';
% always search for zeros. So if we want the crossing of
% any other threshold value "level", we subtract it from
% the values and search for zeros.
S = S - level;
% first look for exact zeros
ind0 = find( S == 0 );
% then look for zero crossings between data points
S1 = S(1:end-1) .* S(2:end);
ind1 = find( S1 < 0 );
% bring exact zeros and "in-between" zeros together
ind = sort([ind0 ind1]);
% and pick the associated time values
t0 = t(ind);
s0 = S(ind);
if ~isempty(ind)
if strcmp(imeth,'linear')
% linear interpolation of crossing
for ii=1:length(t0)
%if abs(S(ind(ii))) >= eps(S(ind(ii))) % MATLAB V7 et +
if abs(S(ind(ii))) >= eps*abs(S(ind(ii))) % MATLAB V6 et - EPS * ABS(X)
% interpolate only when data point is not already zero
NUM = (t(ind(ii)+1) - t(ind(ii)));
DEN = (S(ind(ii)+1) - S(ind(ii)));
slope = NUM / DEN;
slope_sign(ii) = sign(slope);
t0(ii) = t0(ii) - S(ind(ii)) * slope;
s0(ii) = level;
end
end
end
% extract the positive slope crossing points
ind_pos = find(sign(slope_sign)>0);
t0_pos = t0(ind_pos);
s0_pos = s0(ind_pos);
% extract the negative slope crossing points
ind_neg = find(sign(slope_sign)<0);
t0_neg = t0(ind_neg);
s0_neg = s0(ind_neg);
else
% empty output
ind_pos = [];
t0_pos = [];
s0_pos = [];
% extract the negative slope crossing points
ind_neg = [];
t0_neg = [];
s0_neg = [];
end
end
Mathieu NOE on 16 Mar 2022
Direct link to this comment
https://www-ah.mathworks.com/matlabcentral/answers/1666184-extract-data-from-figure#comment_2045374
hello Anton
if my submission has filled your expectations, do you mind accepting it ?
tx
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