transform a matrix with polar coordinates into a matrix with cartesian coordinates

hi, I have two sets of data, each of which I need to process. After the transformation a matrix must come out at the end of each.

i found two approaches. once you can plot them and put a meshgrid on them, and then convert the newly found points. Or you can somehow use pol2cart.

This is recorded data in a helix structure. Always the angle and the radius.

the original matrix data looks like this with imagesc https://imgur.com/a/YT7wuec

and I know something like that is supposed to come out: https://imgur.com/a/toYaqDC

My dataset looks like this: DataSet (512x1000)

in the lines is the radius, and in the columns the angle.

now I want to convert my single elements in the matrix PolMat into cartesian coordinates. And save this matrix as CartMat.

thanks for the help

MATLAB Version: 9.8.0.1380330 (R2020a) Update 2

Answer 1

[KSSV]

Read about pol2cart.

https://in.mathworks.com/help/matlab/ref/pol2cart.html

[Max M]

I have done that, but I can't get the data into a new matrix. With data from the internet and the instructions I can also plot a cartesian picture. But not to store my data in a matrix.

angles = linspace(0, 2*pi, size(PolMat,2));
radii = linspace(1, 100, size(PolMat,1));
[A, R] = meshgrid(angles, radii);
[x,x,z] = pol2cart(A, R, PolMat);
surf(x,y,z)
view(0,90);
shading('interp')

I can only output them graphically in 3D. And then change the view to 2D.

[KSSV]

[x,x,z] = pol2cart(A, R, PolMat);

pol2cart accepts only two inputs.....are you looking for sph2cart ?

https://in.mathworks.com/help/matlab/ref/sph2cart.html..If not share the data.

[Max M]

The documentation says: [x,y,z] = pol2cart(theta,rho,z) transforms corresponding elements of the cylindrical coordinate arrays theta, rho, and z to three-dimensional Cartesian, or xyz, coordinates.

and in the example:

[x,y,z] = pol2cart(theta,rho,z)

that's exactly what I want to do (I think), and with surf you also get a decent picture when you look at it from above. But I would like to save it in a matrix.

i have a spiral (or hold a hose if the spiral is very tight) and no sphere or sphere. So I think sph2cart isn't the right for my purpose.

[KSSV]

I have just checked your DataSet....you got a matrix of size 512*1000...you want to wrap this matrix into a helix ?

[Max M]

yes almost, the data that is available is already a helix, but stored in the individual cells as polar coordinates. I want the same matrix as the Cartesian coordinates.

somehow this works with cart2pol and the (x,y,z) but I can't get it stored in a matrix.

I need a matrix with which I can read the single "heights" with imagesc.

with contur i have now also made it out of my 3 vectors (x,y,z) but i need to get them into a matrix.

contour(x,y,z,[200 200]) %at height of 200

thank you very much for your efforts

[KSSV]

[x,y,z] = pol2cart(A, R, PolMat);
z = double(z) ; 

In the above x, y, z are matrices already.

[Max M]

Now when I run imagesc(z) I get back my original polar matrix image. https://imgur.com/a/YT7wuec

but I would like to have one that looks like my surf(x,y,z) https://imgur.com/a/toYaqDC

• EDIT:
• I think i can get the image also with

contour(Xc,Yc,Zc,[1:512 1:512],'-')

• but my computer can't make with amount of calculation

the records look exactly the same. So PolMat=z only with double instead of uint16

is it not possible to convert the polar matrix polmat into a cartesian matrix and then use imagesc(cartmat) to get the image like in surf? https://imgur.com/a/toYaqDC

[KSSV]

When you try

surf(z)
pcolor(z)

also you will get back your original value. By specifying x,y, you can plot it as a circle or as what you wanted.

[Max M]

yes, but surf(z) is again there picture of my polar data :)

I want the polar data from (z) ((in z the polar data are stored as a matrix))transforming into Cartesian data. And then store this data in a new matrix.

The only thing I'm trying to do is store another matrix that doesn't contain polar data but Cartesian data.