Polar coordinates are used for warping transformation. If you have studied rectangular coordinate system and polar coordinate system in mathematics, it is not difficult to understand this filter. It can map a point at a rectangular coordinate position (x, y) on an image to a point at a polar coordinate position (y/2, x/ image width *2π), or it can be an inverse operation. Of course, it can also be intuitively regarded as the following deformation process:

There is nothing after opening the filter for the following reasons:

1, you selected a layer filled with white.

2. You chose a mask.