# Revision history [back]

### Question about polar or radial angle calculation in the image coordinate system

Hi,

I have general questions, not explicitly about OpenCV, but related to image processing: The image coordinate system normally has the x-axis pointing from left to right, and the y-axis pointing DOWNWARDS. However, in math, normally, the y-axis points upwards. 1) Therefore, is a correction needed to account for the orientation of the y-axis, say, while doing tangentInverse(y, x) to get the radial angle of the pixel location? 2) Will doing y' = height - 1- y, and calling tangentInverse(y', x), solve the problem? (height = image height) 3) The confusion began after I had tried to relate to the formula for the principal value on the "Polar coordinate system" page of wikipedia (specifically, the one that deals with x and y being in different quadrants). I will appreciate, if any expert could clarify. Thank you.

 2 No.2 Revision Alexander Smorkalov 5862 ●2 ●22 ●58 http://alex-alchemist....

### Question about polar or radial angle calculation in the image coordinate system

Hi,

I have general questions, not explicitly about OpenCV, but related to image processing: The image coordinate system normally has the x-axis pointing from left to right, and the y-axis pointing DOWNWARDS. However, in math, normally, the y-axis points upwards. 1)

1. Therefore, is a correction needed to account for the orientation of the y-axis, say, while doing tangentInverse(y, x) to get the radial angle of the pixel location? 2)

2. Will doing y' = height - 1- y, and calling tangentInverse(y', x), solve the problem? (height = image height) 3)

3. The confusion began after I had tried to relate to the formula for the principal value on the "Polar coordinate system" page of wikipedia (specifically, the one that deals with x and y being in different quadrants). I will appreciate, if any expert could clarify. Thank you.

 3 retagged sturkmen 6772 ●3 ●48 ●79 https://github.com/stu...

### Question about polar or radial angle calculation in the image coordinate system

Hi,

I have general questions, not explicitly about OpenCV, but related to image processing: The image coordinate system normally has the x-axis pointing from left to right, and the y-axis pointing DOWNWARDS. However, in math, normally, the y-axis points upwards.

1. Therefore, is a correction needed to account for the orientation of the y-axis, say, while doing tangentInverse(y, x) to get the radial angle of the pixel location?

2. Will doing y' = height - 1- y, and calling tangentInverse(y', x), solve the problem? (height = image height)

3. The confusion began after I had tried to relate to the formula for the principal value on the "Polar coordinate system" page of wikipedia (specifically, the one that deals with x and y being in different quadrants). I will appreciate, if any expert could clarify. Thank you.