How to get the length of flame front

Hi everyone, does anyone know how to code for measuring the length of flame front as seen in the picture above?

My lecturer suggest to me use everyone point (x,y) of the respective temperature to calculate the distance, i'm very new to coding, i appreaciate any help

Here is my csv attachments and matlab code for this 2D surf contour plot

filename = '40um.csv';
Data = csvread(filename,6,0); %read csv data
X_Data = Data(:,2); 
Y_Data = Data(:,1);
T_Data = Data(:,6);

T_Data(T_Data>400)=300; %more than 400K equal to 300

[x,~,xi]=unique(X_Data*1e3/2); %convert m to mm
[y,~,yi]=unique(Y_Data*1e3/2); %option: divide by 2 to use for validations
subs=[xi yi];%use the indices instead of values as coordinates
[X,Y]=ndgrid(x,y);%generate the grid surf() expects

val=T_Data;
M=accumarray(subs,val,[],[],NaN);%fill missing with NaN

surf(X,Y,M); 
surf(-X,Y,M); %Reflection along y-axis

colormap jet
view(0,90),xlabel("x/R (mm)"+newline),ylabel("y/R (mm)"+newline)
xlim([-2 2]); ylim([-0.5 3.4]); c=colorbar; 
title(c,"Temperature",'FontSize',9,'FontWeight','bold'); title('0\circ');
shading interp

[LEONG SING YEW]

here is the csv attachment

Answer 1

[darova]

You have to find first value in each column

ii = zeros(columns,1)
jj = 1:columns;
for j = 1:columns
    ii(j) = find(M(:,j)>200,1,'last');
end
L = hypot(diff(jj),diff(ii));

[LEONG SING YEW]

thanks i work it out with another method, i post here if anyone find it useful

[A B]=size(T_Data);
X_new = zeros(A,1); Y_new = zeros(A,1);
for i = 1:A;
    if T_Data(i,:)>350; 
        X_new(i) = X_Data(i);  %retain the value
        Y_new(i) = Y_Data(i);
    else 
        continue
    end
end
XY = [X_new*1e3 Y_new*1e3]; 
rows = find(XY(:,2)==0);  
XY(rows,:)=[];  %eliminate rows with value zeros

[~,idx] = unique(XY(:,2)); %which rows have a unique first value
XY = XY(idx,:);            %retain them

[~,idy] = unique(XY(:,1));
XY = XY(idy,:);

X = XY(:,1);
Y = XY(:,2);

L = sum(hypot(diff(X),diff(Y))); %length of flame

hold on
plot(-X,Y); plot(X,Y);