Camera models ============= A camera model describes the relationship between 3D :ref:`world ` and 2D :ref:`pixel ` coordinates. Model parameters can be specified with supported :doc:`files <../file_formats/index>`, or directly with the :mod:`~orthority.camera` API. Frame cameras ------------- Orthority uses the term *frame camera* for area-scan cameras like those used in drone and aerial surveys. These cameras capture a 2D image in a single instance of time. The *frame camera* model is a physical model that splits the image formation process into *interior* and *exterior* components, each with its own set of parameters. In a typical drone or aerial survey, *interior* parameters are fixed for a camera, and *exterior* parameters vary for each image. Interior parameters ~~~~~~~~~~~~~~~~~~~ The *interior* component describes the relationship between :ref:`camera ` and :ref:`pixel ` coordinates. It depends on the interior geometry and optical properties of the camera. Interior parameters are: image size, focal length, sensor size, principal point and distortion coefficients. Exterior parameters ~~~~~~~~~~~~~~~~~~~ The *exterior* component describes the relationship between :ref:`world ` and :ref:`camera ` coordinates. It is an affine transform consisting of a translation and rotation. Orthority represents exterior parameters as a world coordinate (*x*, *y*, *z*) camera position, and (*omega*, *phi*, *kappa*) camera orientation, where the (*omega*, *phi*, *kappa*) angles rotate from camera to world coordinates. RPC cameras ----------- The RPC (rational polynomial coefficient) camera model represents the relationship between :ref:`world ` and :ref:`pixel ` coordinates as the ratio of two polynomials. It is a general (non-physical) model typically used for describing narrow field of view and push-broom satellite cameras.