# Simple question on geometry

1. Sep 25, 2004

### mactony

Hi,

I'm rotating an image 105 degrees on a polar grid. I know the top half of the polar grid is 0 degrees to 180 degrees, but what about the bottom half? Is it the same as the top 0 degrees to 180 degrees, or does it go all the way to 360 degrees.

Oops, forgot to clarify in case my question is too vague. Ok, let's say I have an image on the top half of the grid which is 0 degrees to 180 degrees. I have to rotate it , and the new figure would end up on the bottom half the grid. Polar grids are shaped like a circle. I have to map the points of the original image and the new image. Would the bottom image points be 180 degrees to 360 degrees or 0 degrees to 180 degrees.

Last edited: Sep 25, 2004
2. Sep 25, 2004

### Tide

Generally, you would have the polar angle covering 0 to 360 degrees for a full rotation (i.e. it covers both top and bottom) but there is nothing wrong with 0 to 180 (counterclockwise) on the top and 0 to -180 (clockwise) on the bottom starting from the same reference direction (x-axis).

3. Sep 25, 2004

### mactony

So if I was mapping the points, would it be -75 degrees for example, or would it be over 180 degrees, I am just rotating an image.