The Coordinate System, Basic Principles

The coordinate systems used in Flight Simulator are left-hand, 3-D, and rectilinear. Objects are located in and X,Y,Z 3-D space and are moved in the X,Y, and Z directions using translation. The following table describes how this directional translation of an object occurs in the world as well as on the screen.

Dimension	World movement	Screen movement
+X	West to east	Left to right
+Y	Increasing altitude	Bottom to top
+Z	South to north	Into the screen

Flight Simulator directional conventions include the following:

The surface of the earth is laid out on the X-Z plane.
Northerly movement is in the positive Z direction.
Easterly movement is in the positive X direction.
Increasing altitude movement is in the positive Y direction.
World directional movement corresponds to display screen directional movement when the viewer is facing north. For example, an easterly moving object moves to the right across the screen when the viewer is facing north.

Flight Simulator uses Euler angles for rotations; first, heading is applied, then pitch, and, finally, bank. The following table describes the rotational conventions.

Rotation	World rotation	Screen rotation
+Heading, rotate about the Y axis	Rotate to the right; 0° is north	Object moves left as heading increases.
+Pitch, rotate about the heading-rotated X axis	Nose down	Object moves upward (+Y) as pitch increases.
+Bank, rotate about the heading-rotated and pitched Z axis	Rotate counter-clockwise	The object rotates clockwise as bank increases.

Directional translation and rotation are applied to objects before they are projected. The order in which directional translation and rotation are applied makes a difference because the rotations have the effect of "rotating" the coordinate system. Translation and rotation are performed in the following order:

Translate X.
Translate Y.
Translate Z.
Rotate heading (about the Y axis).
Rotate pitch (about the heading-rotated X axis).
Rotate bank (about the heading-rotated and pitched Z axis).