I am currently trying to use spectral-methods to analyse topographic landscapes.
When i FFT the landscape and plot the power-spectrum. From the power-spectrum an orientation of the structures in the landscape can be found.
2D power-spectrum:-
In this power-spectrum, i would like to make a cross-section.
This is easy when the peak amplitude orientation is along the x or y-axis.
But for this area (and others), this is not the case.
Cross-section from another area - orientated along the y-axis:-
My problem is i want to make a cross-section along the peaks in 1, and i just cant seem to figure it out how.
If anyone could point me towards some solution for this. Been stuck here for a couple of days now.
Edit 1
I would like the cross-section, to be a line along the peak orientation.
Edit 2
Improved the first image to show where i want my cross-section
My solution was, as GameOfThrows suggested:
Pick 2 (or more) points on the orientation i want
used Least squares on the points to create the line
Setup a meshgrid for the interpolation.
Use the interp2 function on the new line.
define a proper axis for the section
In my final cross section i ended up having multiple lines in it, that way i was sure to hit the max amplitudes.
i was a little with the answer to my question, but i have been busy :)
You can use ginput built-in matlab function to store 2 (x,y) coordinates of your power spectrum and then use this values to delimit a profile to be interpolated.
Related
I have created the following 3-D barplot:
enter image description here
Now I want to reverse the order of the axis labeled 1 to 5. The reverse function does not work. If I say reverse Y then it reverses the axis labeled 10 to 50 and with Z it reverses the up-down direction.
And I cannot tackle the axis of interest specifically at least I have not yet figured out how to and I am trying since quite a while.
Does anyone know how to handle such a problem specifically in a 3D barplot?
Thank you very much
yannick
I am working with a data stream and for different time points in this stream I have density estimates over a fixed set of X values.
Each of these sets of estimates would look something like this
I'd like to plot multiple curves like this sideways, similar to how it's done in this answer
I've looked through the documentation regarding plotting but didn't find a straight-forward solution for it.
While it's easy to turn such a plot sideways by simply switching the axes, I didn't find a possibility to offset this from the Y-axis
Does anyone have an idea how to tackle this?
Instead of plotting
plot(x,y)
plot
plot(k+y,x)
where k is the location of the plot along the x axis (2 or 4 in your example).
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 have a set of data that I plot but the points on the graphs are so closed to each other that you can't see them well nd neither their values because even when I zoom in I can't get to them all. Now what I want to do is to space them out without changing their actual values on the graph. Is the a function or any other ways to do that? I've tried changing the axis and the scale but it didn't help. Mostly those points are in the Y direction. Please help What I really mean is though these points are closed to each other I'd like to create and interval between them so they don't pile up on each other
You can make the vector you are trying to plot to be more sparse taking points after some defined intervals:
plot(x(1:10:end),y(1:10:end))
In this example, I plotted each tenth point. Does it help?
I have a set of (X, Y) coordinates which, when plotted produce a graph as in the pictures below. What I am trying to do, is to find the coordinates of the areas (corner points) circled in red.
I have been trying to find ways to accomplish this, as those actual turning points represents my area of interest. Please note that I do not have the actual equation for those coordinates.
I would find it grateful if someone could please advise me, or give me some directions on how to go about this, either by using Matlab, or even some other ideas using some C++ tools.
I manage to solve this using a combinaison of the Point Cloud Library and Matlab. The former helped me to separate the coordinates in line segments (RANSAC) and using the latter, I was able to get the Equation of each line segments (Curve Fitting), and simply compute the intersection point through some basic math calculation.