pol2cart with matrices

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prrrrr
prrrrr 2020-7-4
评论： Star Strider 2020-7-5
i have polar coordinates in a matrix 512x500 which can be displayed as in A with imagesc.
I can now convert them into cartesian coordinates. Since it is a spiral they will actually be cylindrical coordinates.
With
angle= linspace(0, 2*pi, size(polvec,2));
rad = linspace(1, 100, size(polvec,1));
[x,y,z] = pol2cart(a,b,c);
figure
surf(x,y,z)
view(2);
I also get a 2-D plot from above (B). But how do I convert this into a real 2-D transfomation? And how do I get a matrix out of it that now stores my data in 2D coordinates?
Thanks
  2 个评论
the cyclist
the cyclist 2020-7-4
Can you upload your data in a MAT file (using the paper clip icon in the INSERT section of the toolbar here)?
prrrrr
prrrrr 2020-7-5
it is a very big file and my internet connection is not s good. I have added an randi in a comment below

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回答（1 个）

Star Strider
Star Strider 2020-7-4
This appears to be the same as: using surf and pol2cart on matrix.
You can get a 2D plot of it by using:
view(0,90)
Another (probably better) option would be to use the contour function instead of surf or mesh. The arguments are the same.
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prrrrr
prrrrr 2020-7-5
编辑：prrrrr 2020-7-5
i think i have it now already so with a random example. the other file is very large.
there i have the surface on the left and the contour on the right. I just don't know how to display the contour at a certain height. So only one slice. and of it I still try to save the matrix, each in a height. and the whole system.
thanks a lot for this great help here. i think matlab is great and i want to learn it (somehow you can do everything with it) but i am still at the beginning,
EDIT: Forgotten the Code :/ sorry
Z = randi([50 300],512,500);
angles = linspace(0, 2*pi, size(Z,2));
radii = linspace(1, 10, size(Z,1));
[A, R] = meshgrid(angles, radii);
[X, Y, Z] = pol2cart(A, R, Z);
subplot(1,2,1);
surf(X,Y,Z)
shading('interp')
grid on
title('surf')
subplot(1,2,2);
contour(X,Y,Z)
title('contour')
Star Strider
Star Strider 2020-7-5
To display the contour at a specific height, specify the height:
contour(X,Y,Z, [150 150])
Here, it will show the contour at 150. (This is described in the documentation.)

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