ctapipe is not stable yet, so expect large and rapid changes to structure and functionality as we explore various design choices before the 1.0 release.

CEP 3 - Dropping Support for Image Parameters in CameraFrame#

  • Status: proposed

  • Discussion: DataPipe F2F Meeting and [#2405], ctapipe developer meeting 2023-11-24

  • Date accepted:

  • Last revised: 2023-09-22

  • Author: Maximilian Linhoff

  • Created: 2023-09-22


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