I have a file with data arranged in three columns. I am trying to make 2D contour plot of these values, where the values in the third column (Z) is projected on the space formed by values in the first (X) and second column (Y). But usual matlab commands like 'contour' and 'imagesc' take the Z-values in the matrix format. Is there a way out in Matlab to plot these values in a 2D-plane?
Contour usually works with two vectors (X and Y) and a matrix (Z). So for each elements of the two vectors (X(i) , Y(i)), there should be a value in the matrix (Z(i,j)). Thus the size of the matrix Z should be equal to the size of the first vector (X) multiplied by the size of the second vector (Y).
if the x,y,z have the same size then you can do something like this:
[X,Y,Z] = meshgrid(x,y,z);
contour(X,Y,Z)
on the other hand if you manage to make the sizes correct then you can do something like this example:
x = linspace(-2*pi,2*pi);
y = linspace(0,4*pi);
[X,Y] = meshgrid(x,y);
Z = sin(X)+cos(Y);
figure
contour(X,Y,Z)
Related
I have two vectors A(1,512), B(1,8) , and one matrix C(8,512). I am trying to plot contour by using contour(X,Y,Z). I do not know to do it.
A vector represents distance, B vector is frequency, and C matrix is velocity.
This can be done by using function contourf(X,Y,Z)
C1=C';
contourf(B,A,C1);
Transposed of C used because length(B) must equal size(C,2) and length(A) must equal size(C,1)
I quote from the documentation:
contourf(X,Y,Z), contourf(X,Y,Z,n), and contourf(X,Y,Z,v) draw filled contour plots of Z using X and Y to determine the x and y values.
I would like to achieve a 3D surface plot. My outputs are as follows.
For a particular value of z, I get y for each value of x (x ranges like 0:0.1:1.4).
Then I vary z and, for the same range of x, I get y values.
The result can be visualised as 2D plots at discrete z values, consisting of the range of x and its corresponding y. Here is my original plot:
I would like to create a 3D surface plot instead, like a blanket wrapped over the above 2D plots.
Here's an example for the two types of plots:
figure
hold on
grid on
view(30,40)
x = 0:.01:4;
z = .3:.3:3;
y = NaN(numel(x), numel(z));
for k = 1:numel(z)
y(:,k) = abs((4-x).*sin(x/(1+z(k)))); % compute a vector as function output
% for input vector x, for each z. Store as a column in matrix y
plot3(x,repmat(z(k),size(x)),y(:,k)) % plot in 3D space
end
figure
surf(x,z,y.','edgecolor','none') % surface plot
view(30,40)
grid on
I have 3 dimensional (X-Y-Z) data which includes-
11 Y vectors (100*1 each (range 0:0.01:1)) each is unique and correspond to the same X vector (100*1 (range 0:0.01:1)). Thus, Y can be treated as matrix with dimension 100*11.
Different Y vectors correspond to different Z values on Z axis (11 values of Z ranging from 0 to 1).
e.g. => Every value of Z on Z axis i.e. Z1=0.05 ... Z11=0.95 has different Y vector for the same X vector. Thus it is like: X-Y1-Z1, X-Y2-Z2, X-Y3-Z3...X-Y11-Z11 (Z1 to Z11 are fixed values like 0.05, 0.1 ,..., 0.95 which are repeated equal to the length of X and Y).
I have already plotted this data as 11 discrete contour lines stacked one above other in 3D space using plot3 hold on. But, I want to create surface out of it. I think I can use interpolation using griddata but I didn't understand how to approach this problem. Can anybody help?
I am charting the following data:
a=[...
0.1, 0.7, 0.00284643369242828;...
0.1, 0.71, 0.00284643369242828;...]
such that column 1 never surpasses approximately 10
also such that column 2 goes from .7 to 1.
Column 3 seems ok
When i chart my surface using surf(a) it looks like this:
it appears not to be properly considering what should be x and y.
anything seem weird there?
I think you need to try one of two things: either break out your height column into its own rectangular matrix Z and use surf(Z) to plot each point relative to its location in the matrix (so your x- and y-axes will not be scaled the way you want), or you can put your desired x- and y-coordinates in their own vectors, and plot the matrix Z (defined at every point (xi, yj) for all i in N and j in M where x is N elements long and y is M elements long) with surf(x,y,Z).
x = 0.1:0.1:10; % or whatever increment you need
y = 0.7:0.01:1; % or whatever increment you need
Z = zeros(length(x),length(y); % initialized to the correct size, fill with data
I think you are going to have to regenerate your Z-data so that it is in a rectangular matrix that is (elements in x) by (elements in y) in dimension.
EDIT: You do not need to recreate your data. If you know that you have n unique elements in x and m unique elements in y, then you can use:
X = reshape(data(:,1),m,n);
Y = reshape(data(:,2),m,n);
Z = reshape(data(:,3),m,n);
surf(X,Y,Z);
And that should give you what you are looking for.
I am trying to create a 2-D grid from a vector.
So, for example I have:
x = 1:1:10;
z = 2:2:20;
Now, I want to create a grid which has x on both side of the grid cell and z as grid cell value.
I tried doing it as :
[X,Y] = meshgrid(x, x);
newZ = griddata(x, x ,z, X, Y);
But this gives me error:
The underlying triangulation is empty - the points may be
collinear.
Need help solving this.
In a high level, griddata() takes a 2d surface with variable z-value at each point as the first part of the input, and the query points as the second part of the input. To be more specific, when we look into the definition of the function:
vq = griddata(x,y,v,xq,yq)
x and y specifies the range of x and y values, v is like z-value in a plane, and xq and yq together are query points. Here, v (in your case, z) is expected to be a 2d matrix, to be more specific, the size of v is [length(x), length(y)], whereas in your case, you put z as a vector. Matlab generates the warning since the size doesn't match.
For your reference: http://www.mathworks.com/help/matlab/ref/griddata.html?refresh=true