Binning 2D set of coordinates
9 views (last 30 days)
Show older comments
I'm pretty new to MATLAB, so sorry if this seems easy. I've got a single long trajectory for a particle below. I have about 100,000 X and Y coordinates from which I've assembled the graph. I'm trying to create a density plot of the coordinates to show where the trajectory is most concentrated. I'm trying to create a density plot of the coordinates to show where the trajectory is most concentrated. I've got the second plot using the following code:
bins = 200;
binsizeX = 3/bins;
binsizeY = 1.2/bins;
xbins = -1.5:binsizeX:1.5;
ybins = -0.6:binsizeY:0.6;
[nx,idxx] = histc(X,xbins);
[ny,idxy] = histc(Y,ybins);
out = accumarray([idxx,idxy], 1);
figure(2);
hold on;
h=imagesc(xbins,ybins,out);hold on;
colorbar; hold on;
axis([-1.5 1.5 -0.6 0.6]); hold on;
But it seems that the density is shifted up and to the right for some reason? Any help is appreciated! Thanks!
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/151356/image.png)
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/151358/image.png)
0 Comments
Answers (4)
alessandro
on 13 Oct 2016
Edited: Walter Roberson
on 13 Oct 2016
Old post, but will try to answer anyway, in case anybody else end up with same issue.
The easiest way to do what you are willing to do is to use hist3 function, with which binning resolution is user dependent and density matrix can be stored easily.
0 Comments
Katalin
on 19 Jun 2015
imagesc flips the image I think. This is from the help: imagesc(x,y,C) displays C as an image and specifies the bounds of the x- and y-axis with vectors x and y. If x(1) > x(2) or y(1) > y(2), the image is flipped left-right or up-down, respectively.
Image Analyst
on 19 Jun 2015
With images, since they are arrays, line 1 (row 1) is at the top, and the line numbers get bigger as you go down the screen. This is the standard custom with images.
With a plot, since it's like regular Cartesian coordinates, where the "y" value increases as it goes up the screen.
The right/left are not flipped, just the up/down. You could use flipud(out) to flip the image vertically before displaying it if you want the plot and image to look similar.
imagesc(xbins, ybins, flipud(out));
2 Comments
Image Analyst
on 20 Jun 2015
Is the centroid supposed to be at (0,0)? Please attach your data file with the paper clip icon, along with code to read it in.
Walter Roberson
on 19 Jun 2015
out = accumarray([idxx,idxy], 1);
should be
out = accumarray([idxy,idxx], 1);
Height (y) is expressed as row number so the y index needs to be first.
2 Comments
See Also
Categories
Find more on Annotations in Help Center and File Exchange
Community Treasure Hunt
Find the treasures in MATLAB Central and discover how the community can help you!
Start Hunting!