Trying to create a filled colour contour plot. Specifically in the form of a depth profile.
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Hello, I am trying to create a depth profile of a stretch of water, with X being Distance, Y being Depth and Z being the coloured fill for Salinity.
I've found it possible to create an X-Y plot of the depth and distance but can't figure how to add the Z and get it as the coloured fill.
I have however already looked at the graph tools section and inputted x, y and z variable inputs, but it still only gives me a graph of x or y.
FYI. each variable was originally in one variable ('num') but i have since seperated into 'Distance','Depth','Salinity'. Also all columns have data of the same length (1;332). Can anyone help me?
10 Comments
Walter Roberson
on 2 Mar 2011
Are your X and Y over grid, or are they scattered ?
Joshua
on 3 Mar 2011
Sarah Wait Zaranek
on 3 Mar 2011
Do you want a filled contour plot (aka contourf)? Or plots x vs y with z being the color of the points (scatter(x,y,z)? Or something else?
Joshua
on 4 Mar 2011
Walter Roberson
on 4 Mar 2011
Please double check that z is the same size and shape as x and y.
You could try scatter3(x,y,z) if the sizes are the same
Matt Tearle
on 4 Mar 2011
What are the sizes returned by:
whos x y z
Joshua
on 4 Mar 2011
Joshua
on 4 Mar 2011
Matt Tearle
on 4 Mar 2011
but scatter(x,z) gives an error? what is the error message?
Joshua
on 4 Mar 2011
Accepted Answer
Matt Tearle
on 4 Mar 2011
For an older version of MATLAB (without TriScatterdInterp):
x = rand(100,1)*4-2;
y = rand(100,1)*4-2;
z = x.*exp(-x.^2-y.^2);
[qx,qy] = meshgrid(linspace(min(x),max(x)),linspace(min(y),max(y)));
qz = griddata(x,y,z,qx,qy);
contourf(qx,qy,qz)
11 Comments
Walter Roberson
on 4 Mar 2011
Matt, that works if your existing data is gridded but the grid is irregular, but the OP's data is just scattered, not on a grid at all.
Joshua
on 4 Mar 2011
Matt Tearle
on 5 Mar 2011
@WR: I don't understand the objection. In my example, x & y are vectors of random points. I don't see how that's any different to Joshua's data, as he's described it. If I do scatter(x,y) I don't see any gridding beyond that which you'd get for any finite data set.
@Joshua: did you run what I posted as it's written? I have no idea where you're getting those numbers (4 & 12000) from. My example creates two vectors of random points, then generates a third vector of z values according to some formula. It then makes a regular grid of finely-spaced points (100-by-100) in the same range as the original data, interpolates the z data onto that grid, and plots the result. To see that the result makes sense, try this
figure
surfc(qx,qy,qz,'facealpha',0.8,'linestyle','none')
hold on
scatter3(x,y,z,'markerfacecolor','b')
Joshua
on 5 Mar 2011
Matt Tearle
on 5 Mar 2011
Unless I misunderstand what you mean, that's what |contourf| does (a plot in x-y axes with colors filling between the z-value contours). I added the |surfc| and |scatter3| example because you said the filled color didn't seem to represent the data. Perhaps you're thinking more of something like
imagesc(qx,qy,qz)
As for the data ranges, MATLAB automatically scales the axes to the data range. Maybe you want to set the aspect ratio of the axes? I can't see that an aspect ratio of 4:12000 is going to give anything visually appealing, but if you want to mess with it so it's not square, use
get(gca,'DataAspectRatio')
to see the current setting, and
set(gca,'DataAspectRatio',[1 20 1])
to change it to something else.
Joshua
on 5 Mar 2011
Matt Tearle
on 5 Mar 2011
Can you please show the full sequence of commands that resulted in the error?
Joshua
on 5 Mar 2011
Joshua
on 5 Mar 2011
Matt Tearle
on 5 Mar 2011
??? Why are you using contourf on the original data?
% load x y z data
[qx,qy] = meshgrid(linspace(min(x),max(x)),linspace(min(y),max(y)));
qz = griddata(x,y,z,qx,qy);
contourf(qx,qy,qz)
Works fine for me, using the x, y, z values you've posted.
Joshua
on 5 Mar 2011
More Answers (1)
Matt Tearle
on 3 Mar 2011
Something like this, perhaps:
% invent some x,y,z data
x = rand(100,1)*4-2;
y = rand(100,1)*4-2;
z = x.*exp(-x.^2-y.^2);
% interpolate onto regular grid
F = TriScatteredInterp(x,y,z);
[qx,qy] = meshgrid(linspace(min(x),max(x)),linspace(min(y),max(y)));
qz = F(qx,qy);
% filled contour plot
contourf(qx,qy,qz)
5 Comments
Sarah Wait Zaranek
on 3 Mar 2011
Exactly what I was thinking, Matt.
Joshua
on 4 Mar 2011
Matt Tearle
on 4 Mar 2011
Ah, I'm guessing you have an old version of MATLAB? In that case, delete that line (obviously), and replace "qz = F(...)" with
qz = griddata(x,y,z,qx,qy);
Joshua
on 4 Mar 2011
Matt Tearle
on 4 Mar 2011
Delete that line. See new answer for the full code
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