how to calculate wavelength of texture ?

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Lyhour Chhay 2022-1-24

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评论： Star Strider 2022-1-25

I have the texture the wavelength as in the figure attachment. I want to calculate the distance from one peak to one peak as show in the figure. How can I calculate it ? thank you very much

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Star Strider 2022-1-24

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Consider using the smoothdata function to eliminate the high-frequency noise. After that, first, use the detrend function to remove the varying baseline (this makles the peak amplitudes and location determinations more reliable), then use findpeaks or islocalmax to locate the peaks. (There are other options if detrend does not produce acceptable results, however it is always the first option I use.)

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Lyhour Chhay 2022-1-24

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Dear Star Strider,

Thank you very much sir. I will send you the .mat file in the given link below. Actually, I am extract the surface profile from the point cloud. I use the code below to extract from the point cloud and calculate the peak distance. However, I notice that it is not so well for cross section profile extraction. It would be better if you could help me to extract the profile from the point cloud with the given coordinate y then I can plot the profile (x,z). Then, I can calculate the peak distance from point cloud more accurately. I am sorry for you inconvienience sir. Thank you very much sir.

https://gwnuackr-my.sharepoint.com/:u:/g/personal/lyhour_gwnu_ac_kr/EWXF-iarV9lLp2GIBiAbjyEBNPnuOAHANu886wzMt8eEwQ?e=3mDJir

clc,clear
ply=pcread('result.ply');
x=ply.Location(:,1)*1000;
y=ply.Location(:,2)*1000;
z=ply.Location(:,3)*1000;
xmin = ply.XLimits(1)*1000;
xmax = ply.XLimits(2)*1000;
ymin = ply.YLimits(1)*1000;
ymax = ply.YLimits(2)*1000;
%% Extract surface profile
F = scatteredInterpolant(x,y,z,'linear','nearest');
xp = linspace(xmin,xmax,length(F.Points));
yp = linspace(ymin,ymax,length(F.Points));
xp = xp';
yp = yp';
zp =F(xp,yp);
%% MWL calucation
[pks,locs] = findpeaks(zp,xp,'MinPeakDistance',3);
plot(xp,zp)
hold all
plot(locs,pks,'ro','MarkerSize',10)
MWL = mean(diff(locs));
fprintf('\n Mean wavelenght is %f \n', MWL); 

Lyhour Chhay 2022-1-25

Dear Sir,

Thank you for your much effort. I really appreciate it. please apology me for the late reply due to different time zone. I understand your suggestion and methodology. Due to my extraction profile is not well smooth, thus, my calculate of mean wavelenght also not so accurate. Therefore, I have to find the good method for profile extraction from point cloud. However, the method that you proposed for calculation between peak distance is acceptable. Thank you very much sir.

Star Strider 2022-1-25

As always, my pleasure!

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