I am currently building a 3D game presented from a 2D isometric viewpoint.
The 3D coordinates start at the top left corner of the screen with x and y increasing towards the right and bottom edges respectively. An angle about the z axis starts with 0 facing right and increases CW.
The isometric coordinates use the diamond method seen in this reference:
My problem is related to choosing the correct frame for my characters. The characters each have a sprite sheet containing an image for one of the 8 compass directions. The start with the image facing right and rotate CW as in the 3D coordinates.
How can I choose the correct sub-image based on their rotation in 3D space? Is the problem is equivalent to converting the rotation into the isometric coordinate space?