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.
Related
If a camera is looking at say 6 evenly spaced dots in the real world it would look like the image below if the camera is looking at the image straight on with no rotation in the x, y or z axis
The z-axis is perpendicular to the image sensor so rotation around the z-axis is simple, it's just a tilt of the image. If I were to rotate the camera (or objects being looked at) around the x axis (if the x-axis is up down) the rows and columns will no longer be parallel and would project off to a vanishing point, like this.
What I would like to do is take a 2 dimensional image of say, dots, and be able to apply different rotations around the x,y and z axes independently. I've experimented with reading my image in Matlab and multiplying by a rotation matrix, or even a full camera matrix but I can't figure out how to take a 2D image, simulate rotating it around the x axis and then saving that back to an image. So that my original grid of dots would look like the bottom image with lines going off to a vanishing point. I've seen some examples using imwarp but I didn't see how I can set the angle of rotation. I'm working on camera calibration so I really want to be able to specify an angle of rotation around each axis.
Thanks for any help.
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 guess, I've got an colormap issue with Matlab2013. I plot a 3d surface plot with colormap hot and I would like to have in the same plot an bitmap (8bit colour image) on the x-y plane. Plotting both separately from each other works fine but as soon as I plot them in one figure the first surface plot is only black. I guess it is because the RGB image on the x-y plane uses a different colour map. Is there an option in Matlab to plot two different type of images in the same plot?
surf(X,Y,density,'FaceColor','texturemap','Edgecolor','none')
colormap hot
...
%// define the location of the bitmap
xImage = [miX maX; miX maX]; %// The y data for the image corners
yImage = [miY miY; maY maY]; %// The x data for the image corners
zImage = [zDist zDist; zDist zDist]; %// The z data for the image corners
surf(xImage,yImage,zImage,... %// Plot the surface
'CData',RGBImage,...
'FaceColor','texturemap');
Thanks!
Durin
I think this is an issue with the relative scaling of density and zImage. I can replicate this by doing the following:
1) Plot a surf where the third input is n x m which is scaled like some real data (-0.2 to +0.2, for example). This responds to changes in colormap as you'd expect.
2) After hold on, plot another surf where the third input is n x m x 3, like a RGB image, double values scaled between 0 and 1.
This causes the first image to go "dark" (or whatever the lowest color in that particular colormap is). The issue is that they share their CLim, being in the same axis, although the RGBImage doesn't, in fact, reference the colormap.
This is "fixable" by scaling/normalising the first plot (your density values) to be between 0 and 1 (in this case) - although this quick fix is going to give you issues if you then want to add a colorbar. Alternatively, first grab the "CLim" from your axis after plotting the first surf:
trueC = get(gca,'CLim');
Then set it back after you plot the image:
set(gca,'CLim',trueC)
Is there some way of using the surf() style data format to create a heat map?
I have a bunch of scattered data of the form z=f(x,y) (so I used TriScatteredInterp to make it work with meshgrid) and I'd like to visualize z with a heat map. surf already does something similar to what I want, except you have to manually rotate the graph so the view is top down looking at the XY plane.
Basically, I'd like something similar to this:
But surf gives you this by default:
Although the answers here already show how to do this with surf, rendering the 3d surface feels a little like overkill...
pcolor creates the required images directly
(with slightly better results -surf has a gap next to the axes)
code
figure(1)
pcolor(peaks)
figure(2)
surf(peaks)
view(2)
results
pcolor
surf
Adding to Ben's answer, you can use the view command. view allows you to rotate your plot to whatever camera angle you wish.
In general, you call the command like so:
view(AZ, EL);
AZ is the azimuth or horizontal rotation, while EL is the vertical elevation. These are both in degrees.
In your case, once you plot your surf plot, use view(0, 90); before you go to the next subplot. view(0, 90); is the default 2-D view, and this looks directly overhead.
By doing this, you avoid having to rotate your plot manually, then using campos to determine what the camera position is at given your plot. view(0, 90); should give you what you need.
Sidenote
Doing view(2); also gives you the default 2D view, which is equal to view(0, 90); as we talked about. By doing view(3);, this gives you the default 3D view as seen in your plots. FWIW, the default azimuth and elevation for a 3D plot is AZ = -37.5, EL = 30, in degrees of course.
Rotate the view to what you want. Then type campos in the terminal. This shows you the camera position. You can then use campos( your_desired ) to set the camera position for future plots.
For example, the x, y view is usually:
campos([4.0000 2.5000 86.6025])
Simple rounded corner rectangle code in Matlab can be written as follows.
rectangle('Position',[0,-1.37/2,3.75,1.37],...
'Curvature',[1],...
'LineWidth',1,'LineStyle','-')
daspect([1,1,1])
How to get the x and y coordinates arrays of this figure?
To get the axes units boundaries, do:
axisUnits = axis(axesHandle) % axesHandle could be gca
axisUnits will be an four elements array, with the following syntax: [xlowlim xhighlim ylowlim yhighlim], it will also contain the zlow and zhigh for 3-D plots.
But I think that is not what you need to know. Checking the matlab documentation for the rectangle properties, we find:
Position four-element vector [x,y,width,height]
Location and size of rectangle. Specifies the location and size of the
rectangle in the data units of the axes. The point defined by x, y
specifies one corner of the rectangle, and width and height define the
size in units along the x- and y-axes respectively.
It is also documented on the rectangle documentation:
rectangle('Position',[x,y,w,h]) draws the rectangle from the point x,y
and having a width of w and a height of h. Specify values in axes data
units.
See if this illustrate what you want. You have an x axis that goes from −100 to 100 and y axis that goes from 5 to 15. Suppose you want to put a rectangle from −30 to −20 in x and 8 to 10 in y.
rectangle('Position',[-30,8,10,2]);
As explained by the comments there appears to be no direct way to query the figure created by rectangle and extract x/y coordinates. On the other hand, I can think of two simple strategies to arrive at coordinates that will closely reproduce the curve generated with rectangle:
(1) Save the figure as an image (say .png) and process the image to extract points corresponding to the curve. Some degree of massaging is necessary but this is relatively straightforward if blunt and I expect the code to be somewhat slow at execution compared to getting data from an axes object.
(2) Write your own code to draw a rectangle with curved edges. While recreating precisely what matlab draws may not be so simple, you may be satisfied with your own version.
Whether you choose one of these approaches boils down to (a) what speed of execution you consider acceptable (b) how closely you need to replicate what rectangle draws on screen (c) whether you have image processing routines, say for reading an image file.
Edit
If you have the image processing toolbox you can arrive at a set of points representing the rectangle as follows:
h=rectangle('Position',[0,-1.37/2,3.75,1.37],...
'Curvature',[1],...
'LineWidth',1,'LineStyle','-')
daspect([1,1,1])
axis off
saveas(gca,'test.png');
im = imread('test.png');
im = rgb2gray(im);
figure, imshow(im)
Note that you will still need to apply a threshold to pick the relevant points from the image and then transform the coordinate system and rearrange the points in order to display properly as a connected set. You'll probably also want to tinker with resolution of the initial image file or apply image processing functions to get a smooth curve.