# 9. ConventionsΒΆ

In raysect the following conventions apply:

- the coordinate system is right-handed
- the x-axis (-ve, +ve) maps to (right, left)
- the y-axis (-ve, +ve) maps to (down, up)
- the z-axis (-ve, +ve) maps to (back, forward)

- object orientation in local space (for general consistency)
- objects with a clear up and forward direction must be aligned such that their forward direction is along the +ve z-axis and their up direction is aligned to point along the +ve y direction
- where objects have an obvious axis of rotational symmetry (e.g. a cylinder or cone) that axis should be aligned with the Z-axis
- where objects have an obvious plane of symmetry, that plane should be aligned with the y-z plane

In raysect.optical:

- dimensions are in meters
- angles are in degrees
- solid angles are in steradians
- wavelength is in nanometers
- power is in Watts
- spectral radiance is in W/m^2/str/nm