I have a surface plot I'm trying to do. x is an 11 element vector, y a 300 element vector and z a 300*11 element matrix.
When I try to plot it like this:
surf(x y z)
The surface plot doesn't show up. The axes are there but there is no surface plot.
However, if for some reason I do a surface plot of a subset of the matrix like this:
surf(x y(1:31) z(1:31,:))
Then it works and the plot shows up.
As soon as I increase the number in the brackets to 32 it stops working. If I change the range from 2:32 then it works, so it's nothing to do with the data just the size of the matrices.
What's going on here? How do I fix it?
P.S I'd attach the code but it's a bit long and complex, and imports .txt files to load into the x and y vectors.
Sometimes, it can help to change Matlab's figure renderer, which is basically the backend that performs the drawing. Options are painters, zbuffer, and OpenGL.
Since it is a figure property, you can apply it to a specific figure, e.g.:
set(gcf(), 'Renderer', 'painters')
or update the default figure properties (if always needed, you could put it in your user-specific startup.m):
set(0, 'Renderer', 'painters')
Similarly, to get the current Renderer state, use get instead of set:
get(gcf(), 'Renderer')
Different renderers have different performance properties (e.g. OpenGL renderer can use hardware acceleration, if supported), but also different quirks (in my experience, frame capturing using getframe() works with some renderers while using remote desktop login, but not all). While I don't know the exact reason for your problem, it may be one of these weird quirks, so try changing the renderer.
From the Renderer property documentation:
Rendering method used for screen and printing.
Selects the method used to render MATLAB graphics. The choices are:
painters — The original rendering method used by MATLAB is faster when the figure contains only simple or small graphics objects.
zbuffer — MATLAB draws graphics objects faster and more accurately because it colors objects on a per-pixel basis and MATLAB renders only those pixels that are visible in the scene (thus eliminating front-to-back sorting errors). Note that this method can consume a lot of system memory if MATLAB is displaying a complex scene.
OpenGL — OpenGL is a renderer that is available on many computer systems. This renderer is generally faster than painters or zbuffer and in some cases enables MATLAB to access graphics hardware that is available on some systems.
Looks at the change in the min/max values of the axis along the left side (y-axis) and the top (z-axis). I think it's still there but it's just very very small.
Try setting the axis afterwards like this:
axis([6E-6 8E-6 9.2E14 10E14 0.96 1.06 -1 1])
Note: the E-6 might be E-8, I can't really tell from the image...
This is based off the code of: axis([xmin xmax ymin ymax zmin zmax cmin cmax])
Related
I would like to produce a plot with two y-axis and two legends, looking something like this:
I have modified a code I found online to produce a high-quality plot to use in reports/papers. I was wondering how you add a second y-axis in such a code? I have attached the matrix and code to produce the high-quality plot: https://drive.google.com/file/d/1aKZLFeoO1wmQ1P2tEiiucvOFI7PehkGL/view?usp=sharing
https://drive.google.com/file/d/1aKZLFeoO1wmQ1P2tEiiucvOFI7PehkGL/view?usp=sharing
NOTE: This is basically a comment, however, it grew too long, and I felt it was too important not to mention properly.
Reporting plots from Matlab should always, unless you have some very good excuse, be done using vector graphics, i.e. pdf, ps, eps or similar format. The reason for this is the quality, e.g. here I have taken your high-quality and the similar pdf-version and zoomed in.
The png version has artifacts. The reason for this is that the png (similar for jpg and more) is that the picture is saved using pixels, thus when you zoom the quality deteriorate.
The pdf version, which is made with vector graphics, save the vectors, thus when I zoom the pdf viewer can regenerate the pixels and maintain the same quality. As an added bonus, the vector-graphic version is typically smaller in size.
This is made in Matlab using
saveas(gcf,'myfigure.pdf')
Use yyaxis to add another plot with an axis. Take a look at the following modified portion of your code.
yyaxis left
plot(N(:,1),N(:,3)/(27.5*2),'b-','DisplayName','Location','LineWidth',lw); %<- Specify plot properites
yyaxis right
plot(N(:,1),N(:,4)/(27.5*2),'r-', 'DisplayName','NorthEast','LineWidth',lw); %<- Specify plot properites
legend('Location', 'NorthEast');
I have 8 plots which I want to implement in my Matlab code. These plots originate from several research papers, hence, I need to digitize them first in order to be able to use them.
An example of a plot is shown below:
This is basically a surface plot with three different variables. I know how to digitize a regular plot with just X and Y coordinates. However, how would one digitize a graph like this? I am quite unsure, hence, the question.
Also, If I would be able to obtain the data from this plot. How would you be able to utilize it in your code? Maybe with some interpolation and extrapolation between the given data points?
Any tips regarding this topic are welcome.
Thanks in advance
Here is what I would suggest:
Read the image in Matlab using imread.
Manually find the pixel position of the left bottom corner and the upper right corner
Using these pixels values and the real numerical value, it is simple to determine the x and y value of every pixel. I suggest you use meshgrid.
Knowing that the curves are in black, then remove every non-black pixel from the image, which leaves you only with the curves and the numbers.
Then use the function bwareaopen to remove the small objects (the numbers). Don't forget to invert the image to remove the black instead of the white.
Finally, by using point #3 and the result of point #6, you can manually extract the data of the graph. It won't be easy, but it will be feasible.
You will need the data for the three variables in order to create a plot in Matlab, which you can get either from the previous research or by estimating and interpolating values from the plot. Once you get the data though, there are two functions that you can use to make surface plots, surface and surf, surf is pretty much the same as surface but includes shading.
For interpolation and extrapolation it sounds like you might want to check out 2D interpolation, interp2. The interp2 function can also do extrapolation as well.
You should read the documentation for these functions and then post back with specific problems if you have any.
I want to construct a 3D cube in MATLAB. I know that the units of any 3D shape are voxels not pixels. Here is what I want to do,
First, I want to construct a cube with some given dimensions x, y, and z.
Second, according to what I understand from different image processing tutorials, this cube must consists of voxels (3D pixels). I want to give every voxel an initial color value, say gray.
Third, I want to access every voxel and change its color, but I want to distinguish the voxels that represent the faces of the cube from those that represent the internal region. I want to axis every voxel by its position x,y, z. At the end, we will end up with a cube that have different colors regions.
I've searched a lot but couldn't find a good way to implement that, but the code given here seems very close in regard to constructing the internal region of the cube,
http://www.mathworks.com/matlabcentral/fileexchange/3280-voxel
But it's not clear to me how it performs the process.
Can anyone tell me how to build such a cube in MATLAB?
Thanks.
You want to plot voxels! Good! Lets see how we can do this stuff.
First of all: yeah, the unit of 3D shapes may be voxels, but they don't need to be. You can plot an sphere in 3D without it being "blocky", thus you dont need to describe it in term of voxels, the same way you don't need to describe a sinusoidal wave in term of pixels to be able to plot it on screen. Look at the figure below. (same happens for cubes)
If you are interested in drawing voxels, I generally would recommend you to use vol3D v2 from Matlab's FEX. Why that instead of your own?
Because the best (only?) way of plotting voxels is actually plotting flat square surfaces, 6 for each cube (see answer here for function that does that). This flat surfaces will also create some artifacts for something called z-fighting in computer graphics. vol3D actually only plots 3 surfaces, the ones looking at you, saving half of the computational time, and avoiding ugly plotting artifacts. It is easy to use, you can define colors per voxel and also the alpha (transparency) of each of them, allowing you to see inside.
Example of use:
% numbers are arbitrary
cube=zeros(11,11,11);
cube(3:9,3:9,3:9)=5; % Create a cube inside the region
% Boring: faces of the cube are a different color.
cube(3:9,3:9,3)=2;
cube(3:9,3:9,9)=2;
cube(3:9,3,3:9)=2;
cube(3:9,9,3:9)=2;
cube(3,3:9,3:9)=2;
cube(9,3:9,3:9)=2;
vold3d('Cdata',cube,'alpha',cube/5)
But yeah, that still looks bad. Because if you want to see the inside, voxel plotting is not the best option. Alphas of different faces stack one on top of the other and the only way of solving this is writing advanced computer graphics ray tracing algorithms, and trust me, that's a long and tough road to take.
Very often one has 4D data, thus data that contains 3D location and a single data for each of the locations. One may think that in this case, you really want voxels, as each of them have a 3D +color, 4D data. Indeed! you can do it with voxels, but sometimes its better to describe it in some other ways. As an example, lets see this person who wanted to highlight a region in his/hers 4D space (link). To see a bigger list I suggest you look at my answer in here about 4D visualization techniques.
Lets try wits a different approach than the voxel one. Lets use the previous cube and create isosurfaces whenever the 4D data changes of value.
iso1=isosurface(cube,1);
iso2=isosurface(cube,4);
p1=patch(iso1,'facecolor','r','facealpha',0.3,'linestyle','none');
p2=patch(iso2,'facecolor','g','facealpha',1,'linestyle','none');
% below here is code for it to look "fancy"
isonormals(cube,p1)
view(3);
axis tight
axis equal
axis off
camlight
lighting gouraud
And this one looks way better, in my opinion.
Choose freely and good plotting!
I have a 3-D plot which I want to cut somehow to show the most interested part and avoid the flat parts (as shown in the picture the blue and orange parts to be the least). I think that it can be done using change of the axis limits in x but different for x_{back} and x_{front} which means I want to change the limits of x front axis to (-20,20) and x back to (-80,-40). How can I do this?
I think krisdestruction is right, it would be such an infrequently-used feature that it's probably not worth the development time or added complexity for TMW to implement.
But you could kludge it. If you were to rotate your data so that the feature aligns with the axes then you could crop the plot to the region of interest as desired. Then hide the grid and draw a new one yourself.
If you're careful you can arrange it so that you can still use the axis labels at the front, which will save you some time, but if not you can always use text to draw new ones on.
I would rotate the data using a rotational transform matrix, which will be pretty quick, and you might be able to pull the gridlines out of the gca object and apply the rotation matrix to those too, which would save you from having to compute them all explicitly.
If you expect to do this more than once or twice then you could encapsulate it all in a nice function that works out the rotation angle from a given pair of 'front' and 'back' axis limits.
Then you can post it to the file exchange : )
I use this command to draw a mesh
trimesh(F, X, Y, Z,...
'EdgeColor','k','FaceColor','flat','FaceVertexCData',c, ...
'CDataMapping','scaled','FaceLighting','flat','BackFaceLighting','lit');
camlight;
When I do this, most faces are lit as expected, but some appear to be unlit; i.e, evern when I rotate the view to other angles and change the light position (as it is dependent on the camera), I still do not see them lit.
It seems to me like a classical problem with the normals (i.e my normal is in the opposite direction), though I thought that in the call to trimesh the arguments 'BackFaceLighting','lit' take care of that.
Any ideas?
Try to set the renderer to opengl by using the following command:
set(gcf,'Renderer','opengl');
It usually handles 3D better than the standard renderer.