Coordinate systems ================== Orthority uses these coordinate systems: Pixel coordinates ----------------- *Pixel coordinates* are 2D *(j, i)* column and row indices of the center of image pixels. Orthority uses the standard convention where the origin is on the top left pixel, the *j*-axis points right, and the *i*-axis points down. Camera coordinates ------------------ *Camera coordinates* are 3D *(x, y, z)* cartesian coordinates aligned with the camera and centered on its optical point. Internally, Orthority uses the OpenCV / OpenSfM convention for these axes, where the *x*-axis points right, the *y*-axis down and *z*-axis forwards (looking through the camera at the world scene). For (*omega*, *phi*, *kappa*) angles supplied in :doc:`CSV <../file_formats/csv>` / :doc:`Orthority exterior parameter <../file_formats/oty_ext>` files or with the :mod:`~orthority.camera` API, Orthority uses the PATB axis convention. In this convention, the *x*-axis points right, the *y*-axis up and the *z*-axis backwards. World coordinates ------------------ *World coordinates* are 3D *(x, y, z)* coordinates where the origin and axis alignment is fixed relative to the Earth. For orthorectification this system is represented by a geospatial CRS (coordinate reference system). :ref:`Frame cameras ` use a cartesian world system, approximated by a projected CRS. :ref:`RPC cameras ` use the WGS84 geographic CRS, optionally transformed to a projected CRS. The ortho image is georeferenced in this coordinate system.