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JESLoooo

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[求助] matlab中quiver3和surfnorm的问题已有1人参与

代码是matlab quiver3函数中的一个例子。输出的图中蓝色矢量是quiver3的结果。然后红色线是另外画的，是surfnorm（x,y,z）的结果。不明白为什么会不一样，surfnorm不就是画出曲面法线的函数么？

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1楼 2017-04-05 13:34:43

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pdl9527

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jjdg: 金币+2, 感谢参与 2017-04-05 16:16:49
JESLoooo: 金币+8, ★★★★★最佳答案 2017-04-05 22:50:21

简单点说是横宽比的问题，两次绘图的横宽比不同所以导致视觉上的不一致，以下是转载的解释。

https://nl.mathworks.com/matlabcentral/answers/100252-why-do-the-surface-norms-calculated-by-surfnorm-and-quiver3-not-coincide-in-matlab-6-5-r13

This is the correct behavior. A unit vector only displays orientation information. The orientation needs to be scaled if the aspect ratio is not the basic [1 1 1] as is in the case of an arbitrary plot. Another way to see this is to think of a line going from [0,1] to [1,1]. Imagine plotting the line in different aspect ratios–the unit vector would have to change to stay normal.

To correct the perceived misalignment with SURFNORM and QUIVER3, you can set both the DataAspectRatio and PlotBoxAspectRatio properties of the Axes Object as shown in the following example code:

CODE:

function question_35

clear;clc

[X,Y] = meshgrid(-2:0.25:2,-1:0.2:1);

Z = X.* exp(-X.^2 - Y.^2);

[U,V,W] = surfnorm(X,Y,Z);

quiver3(X,Y,Z,U,V,W,0.5);

hold on

surf(X,Y,Z);

set(gca,'DataAspectRatio',[1 1 1]);% set data aspect ratio

set(gca,'PlotBoxAspectRatio',[1 1 1]);% set plot box aspect ratio

surfnorm(X,Y,Z);

hold off

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