# plotting a contour of gridded data

Hello

I have gridded data of the shape:

x_1 y_1 z_1
x_1 y_2 z_2
. . .
x_1 y_N z_N

x_2 y_1 z_(N+1)
x_2 y_2 z_(N+2)
. . .
x_2 y_N z_(2N)

x_M y_1 z_(MN)
x_M y_2 z_(MN)
. . .
x_M y_N z_(MN)

I've tried to follow the contour_demo script by making

x = arange(M numbers)
y = arange(N numbers)
X,Y = meshgrid(x,y)

Z = reshape(M, (M,N))

figure()
CS = contour(X,Y,Z)

But I get errors that x and y are not 1D or 2D... Can someone help me
to do this right?
thanks, Peter

Peter I. Hansen wrote:

Hello

I have gridded data of the shape:

x_1 y_1 z_1
x_1 y_2 z_2
. . .
x_1 y_N z_N

x_2 y_1 z_(N+1)
x_2 y_2 z_(N+2)
. . .
x_2 y_N z_(2N)

x_M y_1 z_(MN)
x_M y_2 z_(MN)
. . .
x_M y_N z_(MN)

I've tried to follow the contour_demo script by making

You don't need to make your own X, Y, so delete the following 3 lines.

x = arange(M numbers)
y = arange(N numbers)
X,Y = meshgrid(x,y)

Now you have X, Y, and Z, each as a column in your file, so you need to split them apart and reshape them. Let's assume M, N are the number of X and Y values in your grid; to avoid name confusion, change the load to

X = XYZ[:,0]
X.shape = (M,N)
Y = XYZ[:,1]
Y.shape = (M,N)
Z = XYZ[:,2]
Z.shape = (M,N)

CS = contour(X.transpose(), Y.transpose(), Z.transpose())

The reason for all the transposing is that pcolor and contour display images with column number increasing with X, and row number increasing with Y. Since you have M X-values and N Y-values, everything has to end up N by M, not the reverse.

Eric

···

Z = reshape(M, (M,N))

figure()
CS = contour(X,Y,Z)

But I get errors that x and y are not 1D or 2D... Can someone help me
to do this right?
thanks, Peter

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Perfect. That was just what i needed to know. Thanks!

···

On 7/11/07, Eric Firing <efiring@...202...> wrote:

Peter I. Hansen wrote:
> Hello
>
> I have gridded data of the shape:
>
> x_1 y_1 z_1
> x_1 y_2 z_2
> . . .
> x_1 y_N z_N
>
> x_2 y_1 z_(N+1)
> x_2 y_2 z_(N+2)
> . . .
> x_2 y_N z_(2N)
>
> x_M y_1 z_(MN)
> x_M y_2 z_(MN)
> . . .
> x_M y_N z_(MN)
>
> I've tried to follow the contour_demo script by making

You don't need to make your own X, Y, so delete the following 3 lines.
>
> x = arange(M numbers)
> y = arange(N numbers)
> X,Y = meshgrid(x,y)
>

Now you have X, Y, and Z, each as a column in your file, so you need to
split them apart and reshape them. Let's assume M, N are the number of
X and Y values in your grid; to avoid name confusion, change the load to

X = XYZ[:,0]
X.shape = (M,N)
Y = XYZ[:,1]
Y.shape = (M,N)
Z = XYZ[:,2]
Z.shape = (M,N)

CS = contour(X.transpose(), Y.transpose(), Z.transpose())

The reason for all the transposing is that pcolor and contour display
images with column number increasing with X, and row number increasing
with Y. Since you have M X-values and N Y-values, everything has to end
up N by M, not the reverse.