updirection

Updirection, or the up direction, refers to the orientation of the upward-facing axis in a three-dimensional coordinate system. It is a convention that defines which axis is considered “up” for a given frame of reference and is typically represented by a unit vector pointing toward the upward direction. Updirection is a mathematical and software convention rather than a physical force; gravity defines downward direction, but many applications choose an up-axis for consistency and computation.

In practice, updirection is crucial in fields such as computer graphics, robotics, and geospatial software. It influences how scenes are oriented, how cameras are tilted, and how objects align with the world. Different software packages and data formats adopt different up-axis conventions. Common configurations include Y-up (where the Y axis points up), Z-up (where the Z axis points up), and, less frequently, X-up. The choice of up-axis affects rotation math, including Euler angles, rotation matrices, and quaternions, and must be accounted for when loading, exchanging, or exporting data.

Represented as a unit vector, the updirection may be referred to as the up vector. When integrating data from systems with different conventions, algorithms compute a rotation to align the current updirection with the target up axis, enabling correct orientation of models, cameras, and sensors. Misalignment of updirection across systems can lead to inverted or tilted results, making conversion or reorientation a common preprocessing step in workflows.