why does the surf command give me this result?

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Valeria Leto
Valeria Leto on 9 Oct 2021
Answered: yanqi liu on 10 Oct 2021
Hi! I got this image with
surf(est,nord,down,I_frame,'EdgeColor','none')
where (est,nord) are not regular points.
I know for sure that there are brighter points for example in the region est=(30,40), nord=(-50,-55), but it seems that the darker points preveal over the brigth ones and only them are plotted. Any ideas why this happen? Thank you
  2 Comments
Valeria Leto
Valeria Leto on 9 Oct 2021
Hi @Star Strider I got this image with Face Alpha 0.5. The problem is that I would like only one value, the brigther one. I would like to select it and generate a new image.

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Answers (2)

Star Strider
Star Strider on 9 Oct 2021
I have no idea what the data are, or how the data are being plotted.
If the colormap is gray the ‘brighter’ values are higher ‘z’ values. If those are the ones to be separated and plotted, set a suitable threshold and only plot the data above the threshold. The easiest way to do that is to set all the values below the threshold to NaN.
Example —
v = linspace(-5, 5, 25);
[X,Y] = ndgrid(v);
Z = exp(-(X.^2+Y.^2)*0.1);
figure
surf(X, Y, Z)
colormap(turbo)
title('Original')
figure
surf(X, Y, Z, 'EdgeColor','none', 'FaceAlpha',0.5)
colormap(gray)
view(0,90)
title('Original, Gray Scale, Top View')
Znew = Z;
Znew(Znew<0.5) = NaN; % Set Values Below Threshold To 'NaN' So That They Will Not Plot
figure
surf(X, Y, Znew)
colormap(gray)
view(0,90)
title('Bright Areas')
Experiment to get the desired result.
.

yanqi liu
yanqi liu on 10 Oct 2021
sir, may be use some colormap type to display, such as
colomap hsv

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