How can make I tiny sticks like those shown in red surroundings in the plot below? I used a binary vector of anomalies (1 if anomaly 0 if not) and used plot function, but rather I' d like to see spikes like in the figure.
These sticks correspond to anomaly indicators in the data such as discontinuities (as can be seen in the plot). I'd also like if you could propose good alternative visualizations.
Matlab allows drawing rectangles on the plot.
Related
Is it possible to graphically represent linear transformations in MATLAB like the one shown below?
In particular, I'm looking for a way to represent the way a coordinate grid might become squished, stretched, or rotated after a matrix multiplication has been performed. I've tried using meshgrid(x,y) to plot the grid but I've been having trouble getting it to display properly. Ideally, it would be nice to see the way that the transformation acts on a unit square (and, if possible, to see the transformation being performed in a continuous fashion, where you can see the graphs morphing into each other). However, I'm willing to sacrifice these last two requirements.
Here is the code I have used so far:
x = -10:2:10;
y = -10:2:10;
[X,Y] = meshgrid(x,y);
plot(X,Y)
For some reason, only vertical lines have been plotted. (The documentation says it will display a square grid.)
please read the plot doc.
the problem is that what you are doing is trying to plot mash matrixes in a plot not by using mesh or something like that.
you may find this very helpful.
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 am trying to export filled contour plots from Matlab as vector graphics to include in a Latex file. My current methodology is:
contourf(x,y,v_mag,20), axis([0,width,0,height]),daspect('manual') ;
grid off
colormap jet
h = colorbar;
caxis([0 v_lid])
h.Label.String = 'Velocity Magnitude (m/s)';
set(gcf,'renderer','painters')
export_fig('-painters', '-transparent', 'pdf', 'filename.pdf');
The problem with this method is that it produces artefacts (the white lines) which look like the following:
I understand that these white lines are the polygons defining the shaded areas which have invisible edges, and don't quite overlap (according to here). The problem is caused by the pdf viewer itself which tries to smooth the lines displayed on the screen (according to here). My problem is that most people viewing the document will not know this and will not know how to prevent the viewer doing this. So my questions is:
Is it possible to create a vector graphic of a filled contour plot from Matlab without these artefacts?
Eps produces the same problems. I have tried to use the SVG function but have not had any luck. I am trying to avoid using raster graphics due to the pixelation caused by zooming in. Any advice would be much appreciated.
EDIT - Additional info - Using Matlab v.2014b and Ghostscript v.9.15
This is an extremely frustrating issue for which there seems to be no solution (or even, few attempts at a solution), and it has been many years now. In summary, Matlab cannot cope with outputting artefact-free contour or surface plots (anything with complicated meshes or transparencies).
I can suggest a simple workaround that will work in most cases, where the colours or details of the underlying contour plot do not need to be preserved perfectly.
Output a version of the figure without lines in png format with high enough resolution.
Output a version of the figure without colours in pdf format. This should be free of any artefacts. If your figure it complicated and has many transparencies, you may need to output multiple versions building up the 'levels'.
Use Adobe Illustrator (or some equivalent) to perform a vectorized trace of the raster image. You may lose some detail here, but for simple contour plots with limited details, it will be converted easily to vectorized form.
Overlay the two images within Illustrator. Output in vector format.
This also allows you to use things like Illustrator's ability to compress pdfs.
If you don't want to toy with vectorizing the raster output, you can also simply replace steps 3-4 and combine a raster colour image with a vectorized line image. This would work well for complicated contour plots giving you crisp lines, but the ability to compress the underlying colours.
Eventually, MatLab 2013b doesn't have this problem. Furthermore the files it produces has much less volume. That is because MatLab 2013b composes vectorized image of big overlapping figures, while MatLab 2014b makes that awful meshing.
Here the first file was got with 2013b and the second with MatLab 2014b (I highlighted one of the polygons with red stroke to show the difference). The volumes differ in approximately 22 times (38 Kb vs. 844 Kb).
So it is not the viewer problem, it's how the image is exported from MatLab.
The issue is also discussed here Triangular split patches with painters renderer in MATLAB 2014b and above, but still no direct solution.
I want to get a metric of straightness of contour in my binary image (relatively faster). The image looks as follows:
Now, the contours in the red box are the ones which I would like to be removed preferably. Since they are not straight. These are the things I have tried. I am as of now implementing in MATLAB.
1.Collect row and column coordinates of each contour and then take derivative. For straight objects (such as rectangle), derivative will be mostly low with a few spikes (along the corners of the rectangle).
Problem: The coordinates collected are not in order i.e. the order in which the contour will be traversed if we imaging it as a path. Therefore, derivative gives absurdly high values sometimes. Also, the contour is not absolutely straight, its an output of edge detection algorithm, so you can imagine that there might be some discontinuity (see the rectangle at the bottom, human eye can understand that it is a rectangle though it is not absolutely straight).
2.Tried to think about polyfit, but again this contour issue comes up. Since its a rectangle I don't know how to apply polyfit to that point set.
Also, I would like to remove contours which are distributed vertically/horizontally. Basically this is a lane detection algorithm. So lanes cannot be absolutely vertical/horizontal.
Any ideas?
You should look into the features of regionprops more. To be fair I stole the script from this answer, but here it is:
BW = imread('lanes.png');
BW = im2bw(BW);
figure(1),
subplot(1,2,1);
imshow(BW);
cc = bwconncomp(BW);
l = labelmatrix(cc);
a_rp = regionprops(CC,'Area','MajorAxisLength','MinorAxislength','Orientation','PixelList','Eccentricity');
idx = ([a_rp.Eccentricity] > 0.99 & [a_rp.Area] > 100 & [a_rp.Orientation] < 70 & [a_rp.Orientation] > -90);
BW2 = ismember(l,find(idx));
subplot(1,2,2);
imshow(BW2);
You can mess around with the properties. 'Orientation', 'Eccentricity', and 'Area' are probably the parameters you want to mess with. I also messed with the ratios of the major/minor axis lengths but eccentricity basically does this (eccentricity is a measure of how "circular" an ellipse is). Here's the output:
I actually saw a good video specifically from matlab for lane detection using regionprops. I'll try to see if I can find it and link it.
You can segment your image using bwlabel, then work separately on each bwlabel connected object, using find. This should help solve your order problem.
About a metric, the only thing that come to mind at the moment is to fit to an ellipse, and set the a/b (major axis/minor axis) ratio (basically eccentricity) a parameter. For example a straight line (even if not perfect) will be fitted to an ellipse with a very big major axis and a very small minor axis. So say you set a ratio threshold of >10 etc... Fitting to an ellipse can be done using this FEX submission for example.
Hi i wanted to generate a single axis graph (dont know if this is called a graph exactly) in matlab something like this
In the above image the numerical values represent time ( 1 till 23) min and the vertical thin black lines represent event A . Some of the vertical black lines have a red circle on top denoting occurrence of an event B along with the event A. Is it possible to generate such a simulated image in matlab ? If so what keywords should i look for. Any suggestions to get me quickly started on generating such a graph/Simulation. (Note: I havent actually used matlab a lot.. certainly never generated graphs in it)
You probably want a stem graph, and then do something like:
stem(event_times, ones(size(event_times));
You can overlay multiple graphs to get the red circles, etc.