Contour plot not working (but contour3 plot does work)

Hello everyone,

For some reason when I use the 'contour' function, it just gives me a blank figure. On the other hand, if I use 'contour3' it displays the 3-D contour plot. Any suggestions why this may be happening?

I have a 31x1 double (x-axis), a 19x1 double (y-axis), and a 31x19 double (z-axis).

- First, I use meshgrid with the x and y-axis, which gives me a 19x31 and 19x31 respectively.

- Next, I transpose the z-axis to obtain a 19x31 (just as the other 2 axis)

- Finally, I plot them and obtain the desired surface and mesh plots; but, I am unable to obtain the contour plot as I mentioned above.

Thank you in advance for any help provided.

Answer 1

[David (degtusmc)]

I am still not sure why the 'contour' function did not work for me. It must be some bug in my code.

I ended up using the 'contour3' function. To obtain the regular contour, I use the 'rotate 3D' toolbar and by right clicking on the plot it gives the option to "Go to X-Y view" which is the regular contour.

Answer 2

[Richard McCulloch]

From my understanding, meshgrid will create a matrix out of x and y to provide a 2 dimensional indexing for z. To get a simple 2D contour the vectors have to be the same size. This is because you are essentially defining a z value at an ordered pair (x,y). If the data is linear maybe look at linspace to make them all the same length.

[David (degtusmc)]

Thank you Richard for the answer. After I use meshgrid and I transpose the z-axis, all of them are 19x31.

[Richard McCulloch]

Is your Z a single value? I am getting it to work fine with this example:

x=[1:31]'; y=[1:19]'; z=rand(31,19);
size(x), size(y), size(z)

ans =

      31     1

ans =

      19     1

ans =

      31    19

[x,y]=meshgrid(x,y);
contour(x,y,z')
contour3(x,y,z')

Are any errors showing up? This is a unique problem it seems.

Richard

[David (degtusmc)]

To be completely honest I am not sure what is wrong with it. No errors are showing up and both surface and mesh plots work fine with the same data.

The weirdest part is that, when I went to check if any errors were showing, I commented out the 'contour3' function and replaced it with the regular 'contour' function. I ran it, and it worked!!! Then I deleted the 'contour3' (commented line) and ran it again, but this time it did not work and it has not work since then.

Thanks for the help though.