constrain surf() plot region

Question

Pete 2014-11-10

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/162107-constrain-surf-plot-region

评论： Kelly Kearney 2014-11-11

Hi all, I'm working with the surf(X,Y,Z) function, and trying to force some values to be specific. I'm basically trying to plot a 3D sin-wave, rotationally symmetric about (0,0) and contain a specific number of waves in any direction, then outside this region, force the Z values to zero. Here's code attempts using an 'if' but the Z=0 isn't applied at larger radii than Xmax:

NumberWaves = 2;
Each_Division = 0.1;
X_max = NumberWaves * (2 * pi) ;
X_min = -X_max;
Y_min = X_min;
Y_max = X_max;
[X,Y] = meshgrid(X_min : Each_Division : X_max);
Rad = sqrt (X.^2 + Y.^2 );
if (Rad < X_max)
 Z=0;
else
 Z = (((sin(Rad)) + 1) / 2);
end
figure;
colormap hsv;
surf(X,Y,Z, 'EdgeColor' ,'None');
xlabel('X (**)');ylabel('Y (**)');zlabel('Red Scale');

Alternatively to the forcing Z to a value, I was trying to find references to only plot the surface out to a given radius, which again would be rotationally symmetric. I'm very new to Matlab, so any help appreciated! Thanks!

0 个评论
显示 -2更早的评论隐藏 -2更早的评论

请先登录，再进行评论。

请先登录，再回答此问题。

Answer 1

Kelly Kearney 2014-11-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/162107-constrain-surf-plot-region#answer_158414

在 MATLAB Online 中打开

I would recommend setting up your grid in polar coordinates. The surf command (along with mesh, pcolor, etc.) doesn't require a rectilinear grid, so starting in terms of r and theta allows you to set the cutoff exactly without any setting-to-0 or NaN-masking:

NumberWaves = 2;
Each_Division = 0.1;
rmax = NumberWaves * (2 * pi) ;
r = linspace(0, rmax, 50);
theta = linspace(0, 2*pi, 100);
[r,theta] = meshgrid(r, theta);
z = (sin(r) + 1)./2;
x = r .* cos(theta);
y = r .* sin(theta);
surf(x,y,z);

5 个评论
显示 3更早的评论隐藏 3更早的评论

Pete 2014-11-11

在 MATLAB Online 中打开

OK, all sorted - changed the main line here to:

cmap = ([linspace(0,1,101)'*ones(1,1) linspace(0,0,101)'*zeros(1,2)])

and it's now all working. A handy little tool that will come in useful I'm sure! Many thanks Kelly for this.

Pete

Kelly Kearney 2014-11-11

在 MATLAB Online 中打开

Just so you know, you've got some unnecessary calculations there. You can get the same with

cmap = [linspace(0,1,101)' zeros(101,2)];

请先登录，再进行评论。

Answer 2

Pete 2014-11-10

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/162107-constrain-surf-plot-region#answer_158410

Hi Star Strider,

Surely Xmax is my domain (square in XY), but if I look at +X+Y, the radius is > Xmax, so at this point I would expect the Z value to be forced to zero?

Is there a way to crop the surface? Looking at the figure, ideally I want to set my Z value to 0.5, but the value is arbitrary at this point - or can I crop the graph once 2 waves have been completed?