I am trying to generate a set of views of a 3-D object in Matlab such that the angle changes but the object size stays constant. Because Matlab tries to fit the entire axis into view, an object will shrink or grow depending on whether the plot is viewed head-on or at an angle. As an example:
[x,y,z] = sphere(50); % coordinates of a sphere
surf(x,y,z); % plot the sphere
axis image off
view(0,0) % at this angle the sphere fills the axes
view(-37.5,30) % at this angle the sphere is much smaller
How can I make it so that the sphere appears the same size no matter what angle it's viewed at?
The axis function is your friend here. Try adding
axis vis3d
From the help, "axis VIS3D freezes aspect ratio properties to enable rotation of 3-D objects and overrides stretch-to-fill." If you're interested The same this can be accomplished via
ax = gca;
props = {'CameraViewAngle','DataAspectRatio','PlotBoxAspectRatio'};
set(ax,props,get(ax,props));
Related
If there is an easier way to do this in general any suggestions would be appreciated.
I have imported a .nc file into Matlab and currently have a surface plot created from the interpolated matrix of data which corresponds to longitudes and latitudes. An alpha scale has been applied to add opacity and now I would like to place a map of said longs and lats beneath it so that it acts as an overlay.
here is the code used to plot where xq,yq is the mesh longitude and latitude grid and newMatrix is the interpolated version of the original matrix. Attached is the top view surf plot which I would like a map of long lat restricted x,y axis beneath (line style or topographic)
f = figure;
ax = axes('Parent',f);
h = surf(xq,yq,newMatrix,'Parent',ax);
set(h, 'edgecolor','none');
view(ax,[0,90]);
alpha color
alpha scaled
grid off
colorbar;
I'm aware of geomap but I'm not sure how it can be used in this way without causing the axis to misalign or just not be applied correctly. Before I was using a contour plot but found it easier to interpolate and plot with surf as per this post: Matlab how to make smooth contour plot?
How do I calculate the area of a projection? For example, using the following code, I get a projection on the X-Z plane.
[x,y,z]=peaks;
surf(x,y,z);
xlabel('x');ylabel('y');zlabel('z')
view([0,0])
X-Z Plane Projection
I want to be able to determine the area of the projection of any surf plot that I create. Is there a command or function for this?
Short answer
polyarea(x(1,:),max(z))+polyarea(x(1,:),min(z))
Explanation
The plot you want to calculate its area is,
In area calculation you need only the borders of the projection,
plot(x(1,:),max(z))
hold on
plot(x(1,:),min(z),'r')
and the output is,
The total area is the summation of both areas (upper border to x axis and lower border to x axis),
>> polyarea(x(1,:),max(z))+polyarea(x(1,:),min(z))
>> 28.5947
If you want to get the projection area at an arbitrary view angle, you can use the viewmtx function to project the surface onto the viewing plane, and then use boundary and polyarea to extract the boundary and calculate the area. Something like this:
% draw your surface
[x,y,z]=peaks;
surf(x,y,z);
xlabel('x');ylabel('y');zlabel('z')
axis equal;
%extract the viewing angle, and calculate the resulting transformation matrix
[az,el]=view(gca);
T= viewmtx(az,el);
% transform the surface points by this transformation matrix
pts= [x(:),y(:),z(:),ones(numel(x),1)]';
tpts= T*pts;
tpts=(tpts(1:3,:))';
% now "tpts" has the surface points projected onto the viewing plane
figure, plot( tpts(:,1), tpts(:,2), 'bo'); axis equal;
% calculate the border of this region, and calculate its area.
border = boundary(tpts(:,1), tpts(:,2));
projectedArea = polyarea(tpts(border,1), tpts(border,2));
This approach is based off of the help for viewmtx.
I am currently trying to plot 3D streamtubes. I want the tubes to be colored corresponding to their respective velocity (e.g. slow = blue, fast = red).
To be more exact, I have three 3D-matrices containing the velocity in x, y and z direction. The color of the streamtubes should be sqrt(vx^2+vy^2+vz^2). When using streamtube(x,y,z,vx,vy,vz,sx,sy,sz) the tubes are colored according to their z-coordinate which is useless because it's a 3D plot anyway.
Well this wasn't easy (it ought to be a builtin option), but by modifying the CData of each tube (they are each their own graphics object), you can achieve the desired result. Here's an example
load wind
[sx,sy,sz] = meshgrid(80,20:10:50,0:5:15);
h=streamtube(x,y,z,u,v,w,sx,sy,sz);
drawnow
view(3)
axis tight
shading interp;
This gives this picture:
but then doing this:
vel=sqrt(u.^2+v.^2+w.^2); %// calculate velocities
for i=1:length(h)
%// Modify the colour data of each tube
set(h(i),'CData',interp3(x,y,z,vel,get(h(i),'XData')...
,get(h(i),'YData'),get(h(i),'ZData'),'spline'))
end
drawnow
view(3)
axis tight
shading interp;
gives this result
NOTES:
1) I don't know if this is fully correct, I don't know how to test it
2) You have to interpolate the velocity data from the points where it's known onto the vertices of the streamtubes
3) I found the spline interpolation option to work best, but the other options might work better in other cases
I have generated a rectangular matrix with the azimouth angle changing with rows and the radius changing as you change column. These are meant to represent the relative velocities experienced by a rotating helicopter blade. This produces a matrix called Vmat. I want to plot this to appears in a circle (representing the rotation of the blade)
So far I have tried
[R,T] = meshgrid(r,az);
[x,y] = pol2cart(T,R);
surf(x,y,Vmat(r,az));
which should produce a contoured surface showing velocity as it changes with azimouth angle and radius but it comes up with dimension errors.
I don't mind if it is a 2d contour plot or 3d plot i guess both would be written in a similar way.
Thanks
James
The error is in writing Vmat(r,az), presuming that these are actual values of radius and azimuth, not indexes into your radius and azimuth. If you want to take only a subset of Vmat that's a slightly different matter, but this should work:
[R,T] = meshgrid(r,az); % creates a grid in polar coordinates
[x,y] = pol2cart(T,R); % changes those to cartesian for surf
surf(x,y,Vmat);
Alternatively you could do a contour plot:
h = polar([0 2*pi], [0 max(r)]); % set up polar axes with right scale
delete(h) % remove line
hold on
contour(x,y,Vmat);
I have an image loaded from disk as a texture, and a same-sized matrix d which has the corresponding depths.
How can I use surf to show me the image as a 3d-model? Simply taking
surf(depthMatrix, img);
doesn't give a nice result since
the camera looks not from the x-y plane in z-direction
It looks fairly black
It doesn't look that smooth although my depth matrix is actually smoothed out when I show it using imshow(depthMatrix, []);
You can use texture mapping to display your image on your surface like so:
surf(depthMatrix,img,... %# depthMatrix is z data, img is an image
'FaceColor','texturemap',... %# Use texture mapping
'EdgeColor','none'); %# Turn off edge coloring
And to address your 3 points:
You can adjust your camera angle with the mouse by pressing the button on the figure, which turns on interactive 3-D rotation. You can also turn interactive rotation on using the function ROTATE3D, or you can change the camera view without the mouse using the function VIEW.
Your plot was looking black because edges are drawn as black lines by default, and there were probably a lot of them.
You can adjust the axis scaling and limits to make your surface appear smoother. For example, axis equal will make data units the same for all 3 axes, so your z axis (which ranges from 0 to 25) will be flattened significantly since your other two axes span ranges in the hundreds. Alternatively, in your call to SURF you can specify x and y data to use for the values on those axes, which can ultimately help you to better adjust the relative scaling between those axes and the z axis.