Polar Coordinates not reversible

Report · Aug 05, 2022

Okay, so here's a gripe I've been running into recently: Polar coordinates behavior is weird. It doesn't "unwrap" about the center of the layer. If I stack two polar coordinates on top of each other, one rectangular to polar and one polar to rectangular, I should get an unaltered image, but I don't. This changes depending on the order of the two polar coordinates effects, which it doesn't feel like it should? This has been bothering me for like 8 years now, and I end up bouncing out to photoshop and back...Is this correct behavior? it seems like a bug, but if it is, it's a very old one...

Report · Aug 05, 2022

Why are you not keyframing the interpolation values to reverse the effect? That would unwrap the effect. Rectangular to polar and Polar to rectangular are two completely different algorithms. Polar to Rectangular takes the layer center and moves it counterclockwise to the top center of the layer. Rectangular to Polar takes layer center and pulls it down halfway between layer center and layer bottom. There is no reason that one would reverse the other.

If you add another copy, or Pre-compose and apply the effect, you are applying an effect on top of an effect. I don't know any effect that can undo the result of a duplicate of that effect.

One more point, you can copy and paste an image file, drag it, or use the Toolbar to embed images instead of uploading them. It's a pain to open the uploaded images to see what you are trying to share. Also, cropped screenshots that do not show the modified properties (uu) of the problem layer are useless for diagnosing problems because you cannot see what is happening in the comp. It would help if we understood what you were trying to accomplish in your design.

Report · Aug 05, 2022

Why are you not keyframing the interpolation values to reverse the effect? That would unwrap the effect. Rectangular to polar and Polar to rectangular are two completely different algorithms. Polar to Rectangular takes the layer center and moves it counterclockwise to the top center of the layer. Rectangular to Polar takes layer center and pulls it down halfway between layer center and layer bottom. There is no reason that one would reverse the other.

If you add another copy, or Pre-compose and apply the effect, you are applying an effect on top of an effect. I don't know any effect that can undo the result of a duplicate of that effect.

One more point, you can copy and paste an image file, drag it, or use the Toolbar to embed images instead of uploading them. It's a pain to open the uploaded images to see what you are trying to share. Also, cropped screenshots that do not show the modified properties (uu) of the problem layer are useless for diagnosing problems because you cannot see what is happening in the comp. It would help if we understood what you were trying to accomplish in your design.

By @Rick Gerard

i need to apply in effect in polar space that will be displayed in retangular space, and i need the mapping from rect to pol and back to be the same..."there is no reason one should reverse the other." there is every reason! this is like saying there's no reason two inverts should reverse each other... rect to polar and polar to rect are supposed to be the same operation in two different directions.

Report · Aug 05, 2022

Polar coordinates use two completely different calculations. If the effect has been applied, adding the effect again only adds to the effect. If you wanted to unwrap a circle created by Polat to Rectangular, you would have to invert the math, not use an entirely different calculation. You completely misunderstand how the math works in the two operations and are not following the render order.

Rectangular to Polar takes the original contents of any layer and converts them to a circle by pulling down on the top center of the layer and bending the sides. The distortion is based on layer size, not comp size. The layer size for a shape layer is comp width. Applying Polar coordinates to a shape layer that is 1000 X 1000 is going to look completely different than applying it to a solid that is 1000 X 1000. To make the distortion look identical on a shape layer, you must change the comp size to 1000 X 1000.

When you apply two copies of Polar Coordinates, the second copy is working no longer working on the original shape of the layer, so you can't undo the layer to the original shape. It's as simple as that.

One more thing. The Polar Coordinates effects does not respect transparency, it only work on layer size.

Report · Aug 05, 2022

polar coordinates is a coordinate space transformation, it's supposed to be completely reversible. if i was doing geometry calculations and i needed to convert between two separate coordinate systems, and it behaved this way, that would be a nightmare. that's why every implementation of rectangular to polar coordinates and vice versa i can think of (wolfram, matlab, even photoshop) reverses the process precisely. after effects is the only software i've seen that does it this way.

I need to do effects in polar space that will be displayed in rectangular space, so I need an effect stack like this: rectangular to polar, [effects], polar to rectangular. This works fine in photoshop, and just about everything else out there. Only AE has a different outcome.

Report · Aug 05, 2022

after contemplating the way each effect is implemented, i do understand why it was implemented the way it is in AE, it's so that areas aren't lost in one of the transformations. it's a compromise solution, and it's reasonable, but i don't appreciate you coming in guns blazing telling me there's absolutely no reason they should be reversible. they usually are, whoever wrote this plugin just made a different call on what was more important to keep, accurate coordinates vs not losing data. your answer tells me a lot of what i need to know to work around this problem, and i appreciate it.