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 CSV / Orthority exterior parameter files or with the 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). Frame cameras use a cartesian world system, approximated by a projected CRS. RPC cameras use the WGS84 geographic CRS, optionally transformed to a projected CRS. The ortho image is georeferenced in this coordinate system.