why does the surf command give me this result?

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Valeria Leto 2021-10-9

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https://ww2.mathworks.cn/matlabcentral/answers/1470236-why-does-the-surf-command-give-me-this-result

回答： yanqi liu 2021-10-10

immagine.PNG

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

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Star Strider 2021-10-9

在 MATLAB Online 中打开

One optiion could be to add a 'FaceAlpha' value —

surf(est,nord,down,I_frame,'EdgeColor','none', 'FaceAlphs',0.5)

That would make all of them semi-transparent, allowing those that are otherwise ‘covered’ to be seen. Change that value (going from 0 to 1) to get the desired result.

.

Valeria Leto 2021-10-9

im.PNG

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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Answer 1

Star Strider 2021-10-9

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https://ww2.mathworks.cn/matlabcentral/answers/1470236-why-does-the-surf-command-give-me-this-result#answer_805006

在 MATLAB Online 中打开

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)