In matlab I need to create a mesh (surf) of a function.
then I need to show the mesh contour lines.
in the end I need to show with arrows the contour lines direction.
I have this so far:
mesh(T); //T is the matrix [150x200] created by the function, this present me the mesh
contour(T);//this present me the contour lines
[px py]=gradient(T);//this for calculate gradient of T (px is[150x200] and also py)
contour(T), hold on, quiver(px,py), hold off //quiver is to make arrows
This work fine, I can see the contour lines but my problem is that the arrows are too crowded and what i'm seeing it not very clear.
I need to diluted px and py but I don't know how.
I don't know if it is something I need to do before the gradient function or after.
I need that px and py will stay on [150x200] and maybe replace some value in them to zero,
Thank you all!
I'd "dilute" the arrow, (px,py) by sampling just a subset of them. For example:
N=25; % or usea different # of points if needed
range1=unique(round(linspace(1,size(T,1),N)));
range2=unique(round(linspace(1,size(T,1),N)));
[rx ry]=meshgrid(range1,range2);
quiver(rx,ry,px(range1,range2),py(range1,range2)); %, hold off
Related
I have a Matlab plot that contains relatively high amount of different data and hence if i use standard legend representation, i could not figure out which legend color belongs to which curve.
So, is there any way to put legends on each curve? Lets say "BUS7" text should be located on the purple curve (undermost one).
Thanks.
I am trying to do something like this:
The text(x, y, txt) function allows you to add text at a given location on the plot. link.
Looking at your example, it seems that you want to have all the labels on the left-hand side. So, one way to do it would be like this, where I have generated my own dummy data:
leg = {'First Curve', 'Second Curve', 'Third Curve'};
figure;
x = linspace(1,10,100);
for ii = 1:3
y = x + ii*10;
plot(x, y);
hold on
text(x(1), y(1)+2.5, leg{ii});
end
Regretfully, this does not do anything clever with where the label is placed - it is merely placed slightly above the first point of the curve. You can clearly easily move it along the curve, but if you have many curves, like in your case, the labels will likely overlap and you will need to tinker a bit to avoid this.
I am trying to write a MATLAB script to give me a contour map. The contour map must be created from inputs that I generated from 100 images.
The story is like this:
I have 100 images on which I ran an image processing algorithm for optimization. Now, I got their energy curves. So, I have 100 energy curves. I want to create a contour map that will show me where the points are denser on the plot. (the energy curves are plotted as energy vs. iteration with fixed number of iterations)
The following is my variable:
energy(iteration,numImages)
Hope I explained it well.
Thanks in advance.
I interpret your question to boil down to how can I create a surface plot with colors according to the energy found in energy. I would solve this by using the contour function with a grid generated using meshgrid. If each image is described in 1000 data points with 100 files the plot can be generated as follows:
% using stuff as random junk instead of energy
numPoints = 1000;
numFiles = 100;
stuff = rand(1000,100); % replace with actual information
[X, Y] = meshgrid(1:numFiles, 1:numPoints);
contour(X,Y,stuff);
You can also create a 3D surface plot using surf and the same logic.
From what i see of you graph (and using the comments also), one possible way is to use plot3 to plot a line in 3D for every plot.
For doing so, you can use something like this code:
x=(0:0.01:1)';
aexp=zeros(100,numel(x));
hold on
for ii=1:100;
% aexp(ii,:)=exp((-x+ii/10)); %exponential
aexp(ii,:)=exp(-(x-ii/100).^2); %~gaussian
% aexp(ii,:)= x*ii; %linear increase
plot3(x,aexp(ii,:),ii*ones(1,numel(x)));
end
% set(gca,'yscale','log'); % uncomment if you need logscale.
giving
I have a few options of plot. It always plot from the XY view. I changed by hand, but you can use the view command. Notice that i used a simple counter to make the spacing in the z direction.
In a similar manner, you can plot using the contour. For my code, after the data have been generated in the for loop, remove/comment the plot3 and add:
contour(aexp) %outside the for loop,
giving
Notice that i have not really take care what i'm plotting. You can find more info on contour in the Matlab page .
You commented that the x-axis should be number of iterations, y-axis should be energy and z-axis should be the information containing how many lines are passing through from some areas. For this, make a qq variable, being it qq=number_of_lines(number of iterations,energy) . Make a discrete grid for the energy if you don't have one. Number of iterations is probably discrete anyway. The function is you who need to devise, but i would go for something which checks the number of lines for every energy and every iteration. In this case you will have the z-function that depends on y and x, that is the case to use contour or surface.
My function above make a line for every ii point, to have a 3d function. An edition for another extra loop is not hard. Just remember to have the same regular grid for every point, otherwise you will have trouble.
When determining points within polygons using MATLAB's inpolygon function, I find that the results are exactly correct for polygons drawn on linear axes but only approximately correct for polygons drawn on log-scale axes. Although my suspicions lean in favor of a MATLAB bug, it's possible I've overlooked something.
The following code reproduces the issue I have been experiencing with other data. The results are shown in the following image (the bottom set of panels are zoomed views of the top panels). One can appreciate that there are unlabeled points inside the polygon and labeled points outside the polygon, neither of which should occur, in the case of a polygon drawn on log-scale axes (right). In contrast, the polygon test is exact for polygons drawn on linear axes (left).
n=2E4;
x(:,1)=rand(n,1); y(:,1)=rand(n,1);
x(:,2)=lognrnd(0.5,0.25,n,1); y(:,2)=lognrnd(0.5,0.25,n,1);
for m=1:2
subplot(1,2,m);
scatter(x(:,m),y(:,m),'.'); hold on;
if(m==2)
set(gca,'xscale','log'); set(gca,'yscale','log');
end
p=impoly(gca);
pc=getPosition(p);
in=inpolygon(x(:,m),y(:,m),pc(:,1),pc(:,2));
scatter(x(in,m),y(in,m),20);
end
I think you missed something: A line in normal scale is not a line in log scale. Your polygons are not properly drawn in the log scale, as you draw 2 points and put them together with a straight line.
Look at the real polygon in log space:
close all
clear
n=2e4;
x(:,1)=rand(n,1); y(:,1)=rand(n,1);
x(:,2)=lognrnd(0.5,0.25,n,1); y(:,2)=lognrnd(0.5,0.25,n,1);
for m=1:2
subplot(1,2,m);
scatter(x(:,m),y(:,m),'.'); hold on;
if(m==2)
set(gca,'xscale','log'); set(gca,'yscale','log');
end
p=impoly(gca);
pc=getPosition(p);
% plot polygon
hold on
for ii=1:size(pc,1)-1
plot(linspace(pc(ii,1),pc(ii+1,1),100),linspace(pc(ii,2),pc(ii+1,2),100),'g')
end
plot(linspace(pc(end,1),pc(1,1),100),linspace(pc(end,2),pc(1,2),100),'g')
in=inpolygon(x(:,m),y(:,m),pc(:,1),pc(:,2));
scatter(x(in,m),y(in,m),20);
end
Look at this zoomed in result (click to enlarge):
This happens because the polygon is defined in euclidean space, and it is defined as points linked by lines. If you want to work in log space, things may get complicated. One way to numerically approximate it is the inverse of what I did for plotting. Create dense enough sampled straight line on log space, convert it to linear space, and define a high vertex polygon with the resulting points. Then use inpolygon.
I have a figure which consists of different levels of a contour plotted using the hold on function. I want to fill the space between the levels of contour with a color. Could you please assist me how can I do that. I have already tried the contourf function. The figure consists of different red colored levels of a contour, what I want is a solid color filled between these contour levels.
I am not sure if I got exactly what you wanted but here goes a possible solution to your problem.
If you plotted using the hold on function I would therefore assume you have each contour in a different variable. If so you can use logic to check whether a contour is higher or lower relatively to another. If your problem is that you do not have the same x axis for each so that you can use logic just interpolate for each contour (for example between -0.8 and 0.8)
I will give an example of what I am saying. See if this helps.
%simulated contours
x=linspace(0,pi,100);
y = sin(x);
y2 = sin(x)*2;
y3 = sin(x)*3;
figure, hold on,
plot(x,y),
plot(x,y2),
plot(x,y3),
%fill contours
[X,Y]=meshgrid(x,0:3/100:3);
zzz=(Y<repmat(y,size(Y,1),1))+(Y<repmat(y2,size(Y,1),1))+(Y<repmat(y3,size(Y,1),1));
figure,imagesc(zzz)
set(gca,'YDir','normal')
I want to assign vector to a contourf graph, in order to show the direction and magnitude of wind.
For this I am using contourf(A) and quiver(x,y), where as A is a matrix 151x401 and x,y are matrices with the same sizes (151x401) with magnitude and direction respectively.
When I am using large maps i get the position of the arrows but they are to densily placed and that makes the graph look bad.
The final graph has the arrows as desired, but they are to many of them and too close, I would like them to be more scarce and distributed with more gap between them, so as to be able to increase their length and at the same time have the components of the contour map visible.
Can anyone help , any pointers would be helpful
i know its been a long time since the question was asked, but i think i found a way to make it work.
I attach the code in case someone encounters the same issues
[nx,ny]= size(A) % A is the matrix used as base
xx=1:1:ny; % set the x-axis to be equal to the y
yy=1:1:nx; % set the y-axis to be equal to the x
contourf(xx,yy,A)
hold on, delta = 8; %delta is the distance between arrows)
quiver(xx(1:delta:end),yy(1:delta:end),B(1:delta:end,1:delta:end),C(1:delta:end,1:delta:end),1) % the 1 at the end is the size of the arrows
set(gca,'fontsize',12);, hold off
A,B,C are the corresponding matrices ones want to use