MATLAB Central Newsreader - Converting an image from polar to cartesians?

Converting an image from polar to cartesians?

petros dias — Thu, 18 Jun 2009 20:21:03 -0400

Hi everyone,

I'm trying to convert an image from polar to cartesian coordinates. I am assuming my polar image is an image that has a 0,0 at top-left and the two dimensions do need to match (the horizontal being the radius and the vertical being theta).

I am using "interp2" to interpolate all the positions in the cartesian coordinates. Using this function, I would need to provide X,Y, XI,YI, while X,Y being the indices of the location of the pixels provided, while XI, YI the indices of the positions that need to be calculated.

I tried different ways to make this work, but I can't get it to work. Does anyone have a clue on how to do this? I even found another ready function that does this transformation, but I would still need to provide X,Y, XI, YI, which I don't know how to calculate.

Any help is appreciated.

Re: Converting an image from polar to cartesians?

Nicolaie Popescu-Bodorin — Fri, 19 Jun 2009 01:08:01 -0400

Hello Petros,

for something like this

http://www.limbistraine.com/ro/software/popescu-bodorin/img/circular-fast-fuzzy-iris-segmentation-popescu-bodorin-nicolaie.jpg

see the following link:

http://en.wikipedia.org/wiki/List_of_canonical_coordinate_transformations#To_Cartesian_coordinates_from_polar_coordinates

Bodorin

"petros dias" <p.dias@ucl.ac.uk> wrote in message <h1e7jf$5lh$1@fred.mathworks.com>...
> Hi everyone,
>
> I'm trying to convert an image from polar to cartesian coordinates. I am assuming my polar image is an image that has a 0,0 at top-left and the two dimensions do need to match (the horizontal being the radius and the vertical being theta).
>
> I am using "interp2" to interpolate all the positions in the cartesian coordinates. Using this function, I would need to provide X,Y, XI,YI, while X,Y being the indices of the location of the pixels provided, while XI, YI the indices of the positions that need to be calculated.
>
> I tried different ways to make this work, but I can't get it to work. Does anyone have a clue on how to do this? I even found another ready function that does this transformation, but I would still need to provide X,Y, XI, YI, which I don't know how to calculate.
>
> Any help is appreciated.

Re: Converting an image from polar to cartesians?

petros dias — Sat, 20 Jun 2009 12:41:01 -0400

Thanks , but I already know how to perform that transformation, my question was on the usage of the interp2 algorithm and its' inputs.

Either way, I already found a function that works very well, provided here:

http://www.mathworks.com/matlabcentral/fileexchange/17933

"Nicolaie Popescu-Bodorin" <freeseosubmit@yah00.com> wrote in message <h1eodh$k7b$1@fred.mathworks.com>..."