diff --git a/docs/developer-guide/ceps/proposed/cep-003-remove-image-parameters-in-camera-frame.rst b/docs/developer-guide/ceps/proposed/cep-003-remove-image-parameters-in-camera-frame.rst new file mode 100644 index 00000000000..463df4ac2a5 --- /dev/null +++ b/docs/developer-guide/ceps/proposed/cep-003-remove-image-parameters-in-camera-frame.rst @@ -0,0 +1,52 @@ +.. _cep-003: + + +************************************************************ +CEP 3 - Dropping support for image parameters in CameraFrame +************************************************************ + +* Status: draft +* Discussion: NA +* Date accepted: NA +* Last revised: 2023-09-22 +* Author: Maximilian Linhoff +* Created: 2023-09-22 + +Abstract +======== + +Currently, ctapipe supports computing all image parameters in two variants: + +* Using a ``CameraGeometry`` where pixel coordinates are expressed in ``CameraFrame``, i.e. + in length units (most commonly meters) on the camera focal plane. +* Using a ``CameraGeometry`` where pixel coordinates are expressed in ``TelescopeFrame``, i.e. + in angular units (most commonly degree) on sky. + +We propose to drop support for the first, to simplify code in multiple places and reduce +possibility for confusing the two similar variants of the image parameters. + +The overhead of supporting both ``TelescopeFrame`` and ``CameraFrame`` representations +of the image parameters is quite significant, as it e.g. requires dealing with both +possible definitions in all Hillas-style dl2 reconstructors. + +Advantages of computation in TelescopeFrame +=========================================== + +Computing the image parameters in ``TelescopeFrame`` – angular units on the sky – +has the following advantages: + +* Parameters are easier to compare across different telescope types. +* Pointing corrections can directly be applied in the conversion from ``CameraFrame`` + to ``TelescopeFrame`` and are then automatically included in the image parameters, + which is much more straight forward than trying to correct image parameters that + are affected to different degrees after they have been computed. +* Conversion from ``CameraFrame`` to ``TelescopeFrame`` will include any necessary + special handling of the curved cameras of dual mirror telescopes. + + +Previous discussions +==================== +* Issue discussing the removal of the camera frame image parameters: `#2061 `_ +* Original issue for introducing the computation of image parameters in telescope frame: `#1090 `_ +* Pull Request implementing image parameters in telescope frame, also setting it as the default: `#1591 `_ +* Adapting the reconstructors to also work with image parameters in telescope frame: `#1408 `_