I have a script to create scatter plots (using gscatter) based on x-y data (discrete data points, not continuous) produced by another script. Since these data points are actually the locations of certain objects in a circular space, adding polar grid lines will make the plots more meaningful.
Does anyone know how to show polar grid lines on a Cartesian scatter plot, or am I better off using polar plots?
I once made this script for drawing a polar coordinate system on top of a regular plot. Perhaps it can be useful for you. It is based on this script but simplified to only draw the coordinate system and no data. If this wasn't what you were looking for, check out the linked script, perhaps it can help as well.
Be sure to tweak the radius as needed! I usually disable the axis but it's up to you to fix that if you need another look :)
R=6000; %radius
S=10; %num circ.lines
N=10; %num ang.lines
sect_width=2*pi/N;
offset_angle=0:sect_width:2*pi-sect_width;
%------------------
r=linspace(0,R,S+1);
w=0:.01:2*pi;
clf %remove if needed
hold on
axis equal
for n=2:length(r)
plot(real(r(n)*exp(j*w)),imag(r(n)*exp(j*w)),'k--')
end
for n=1:length(offset_angle)
plot(real([0 R]*exp(j*offset_angle(n))),imag([0 R]*exp(j*offset_angle(n))),'k-')
end
%------------------
You can always use the pol2cart function to generate the polar grid lines.
For example:
function DrawGridLines
x = randn(10);
y = randn(10);
figure;scatter(x(:),y(:));
hold on ;
for angle = 0:20:(360-20)
[x1,y1] = pol2cart( angle / 180 * pi , [0 2]);
plot(x1,y1,'r')
end
for rho = 0:0.1:2
[x1,y1] = pol2cart( 0:0.01:2*pi , rho);
plot(x1,y1,'b')
end
axis equal
end
Related
I have made a function that allows a user to draw several points and interpolate those points. I want the function to calculate the centre of mass using this vector :
I think I should therefore first calculate the area of the figure (I drew this example to illustrate the function output). I want to do this using Green's theorem
However since I'm quite a beginner in MATLAB I'm stuck at how to implement this formula in order to find the centre of mass. I'm also not sure how to get the data as my output so far is only the x- and y cordinates of the points.
function draw
fig = figure();
hax = axes('Parent', fig);
axis(hax, 'manual')
[x,y] = getpts();
M = [x y]
T = cumsum(sqrt([0,diff(x')].^2 + [0,diff(y')].^2));
T_i = linspace(T(1),T(end),1000);
X_i = interp1(T,x',T_i,'cubic');
Y_i = interp1(T,y',T_i,'cubic');
plot(x,y,'b.',X_i,Y_i,'r-')
end
The Center Of Mass for a 2D coordinate system should just be the mean of the interpolated x-coordinates and y-coordinates. The Interpolation should give you evenly spaced coordinates which you can use to your advantage. So simply add to your existing function:
CenterOfMass= [mean(X_i),mean(Y_i)]
plot(x,y,'b.',X_i,Y_i,'r-')
hold on
plot(CenterOfMass(1),CenterOfMass(2),'ro')
should give you the center of mass assuming that all points are weighted equally.
So I have data in the form [x y z intensity] that I plot on a scatter3 figure with xyz axes. The colour of the data is used to dictate the intensity value. Problem is, using a scatter plot means the data points show up as discrete points. What I need, is a smooth shape - so I guess I need some kind of interpolation between the points?
I've tried using trisurf, but the problem with this one is that it interpolates between points that it shouldn't. So where I should have 'gaps' in my surface, it joins up the edges instead so it fills in the gaps. See the attached pics for clarification.
Does anyone have any suggestions?
The code I use is as below (the commented out scatter3 is what does the scatter plot, the rest does the trisurf):
% Read in data
dataM = csvread('3dDispersion.csv');
% scatter3(dataM(:,1), dataM(:,2), dataM(:,3), 5, dataM(:,4),'filled');
% Plot
hold on;
x = dataM(:,1);
y = dataM(:,2);
freq = dataM(:,3);
tri = delaunay(x,y);
h = trisurf(tri, x, y, freq);
% Make it pretty
% view(-45,30);
view(3);
axis vis3d;
lighting phong;
shading interp;
Use the boundary function in Matlab. This will apply a mesh similar to shrinkwrap over your points. In order to reduce the "gap closers", you will want to increase the "shrink factor".
Try K = boundary(X,Y,Z,0.9)
Where X, Y & Z are the vectors of your data points
https://www.mathworks.com/help/matlab/ref/boundary.html
You can then use trimesh or related surface plotting functions depending on how you want to display it.
I would like to plot a line, and in grey-shaded X% deviation of a signal, in MATLAB. Then, I'd plot another signal and see (visually) how much of the second signal is outside the gret-shaded area.
The task I'd like to get help done is the shaded area: similar to the image attached below.
I am aware of similar solutions with errorbar, but I think this is a much clearer plot to visualize.
If for example I had:
x = 0:0.1:10;
y = 1 + sin(x);
What would the 5% grey-shaded plot of y look like? (that area?)
See this answer for an example: MATLAB fill area between lines
Do you have the error of y at each sample in x? Let's assume you have and the upper bound is in variable yu and the lower bound in variable yl. Then you could plot it using:
x = 0:0.1:10;
y = 1 + sin(x);
% I create some yu and yl here, for the example
yu = y+.1;
yl = y-.1;
fill([x fliplr(x)], [yu fliplr(yl)], [.9 .9 .9], 'linestyle', 'none')
hold all
plot(x,y)
fill(X,Y,ColorSpec,...) plots a polygon with edges specified in the first two parameters. You have to fliplr (flip left-right) the arrays, so that it correctly draws the shape of the area to be filled 'in a circle' around it. The [.9 .9 .9] is the colour specification, in this case a light grey. I removed the edge by setting no line, to make it even more similar to your desired plot. One detail: plot the filled area before plotting y, because the last plotted object goes on top of the others.
I have generated a rectangular matrix with the azimouth angle changing with rows and the radius changing as you change column. These are meant to represent the relative velocities experienced by a rotating helicopter blade. This produces a matrix called Vmat. I want to plot this to appears in a circle (representing the rotation of the blade)
So far I have tried
[R,T] = meshgrid(r,az);
[x,y] = pol2cart(T,R);
surf(x,y,Vmat(r,az));
which should produce a contoured surface showing velocity as it changes with azimouth angle and radius but it comes up with dimension errors.
I don't mind if it is a 2d contour plot or 3d plot i guess both would be written in a similar way.
Thanks
James
The error is in writing Vmat(r,az), presuming that these are actual values of radius and azimuth, not indexes into your radius and azimuth. If you want to take only a subset of Vmat that's a slightly different matter, but this should work:
[R,T] = meshgrid(r,az); % creates a grid in polar coordinates
[x,y] = pol2cart(T,R); % changes those to cartesian for surf
surf(x,y,Vmat);
Alternatively you could do a contour plot:
h = polar([0 2*pi], [0 max(r)]); % set up polar axes with right scale
delete(h) % remove line
hold on
contour(x,y,Vmat);
I just have a brief question regarding MatLab.
Say that we have the equation:
r^2 = 2 sin(5t)
I know that I can fill a polar plot by writing, say:
t = linspace(0,2*pi,200);
r = sqrt(abs(2*sin(5*t)));
x = r.*cos(t);
y = r.*sin(t);
fill(x,y,'k')
But say I use the ezpolar instead by giving the equation above a function handle and then typing:
ezpolar(function handle)
Is there any way I can then fill this polar plot? Or do I have to use the procedure outlined above?
Any tips/help will be greatly appreciated!
You can use ezpolar, then modify the resulting figure. If you look at the returned handle from ezpolar, you'll see it is the line itself drawn in the axis. The points from that line object can be extracted, then used to lay a new polygon on top of the same axis. The benefit is, you get to keep all the nice polar lables.
h=ezpolar('sqrt(abs(2*sin(5*t)))')
hold on;
fill(get(h, 'XData'), get(h, 'YData'), 'k');