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Tilts

Overview

This file describes the data model for the Tilts.

The images are written to disk as a multi-extension FITS file prefixed by Tilts in the Calibrations/ folder. See :ref:`calib-naming` for the naming convention.

Inspecting

To examine the quality of this step the user can run the pypeit_chk_tilts script, or inspect the PNG files generated by the code. :doc:`../qa` describes how to access them.

pypeit_chk_tilts

There are currently 2 options for viewing the traced and 2D fitted tilts on the image used to construct them. Each uses the pypeit_chk_tilts script.

ginga

This is the default mode when executing, e.g.:

pypeit_chk_tilts Calibrations/Tilts_A_0_DET01.fits

The :doc:`tilt` image is shown in ginga with the traced and 2D fitted tilts over-plotted.

Here is a zoom-in screen shot for the shane_kast_red spectrograph.

../figures/pypeit_chk_tilts.png

You want to check that the traced and 2D fitted tilts overlay well on the arc/OH lines.

matplotlib

To avoid ginga, use the --mpl flag:

pypeit_chk_tilts Calibrations/Tilts_A_0_DET01.fits --mpl

QA PNG files

There are 3 PNG files generated per slit:

2D Arc Tilts

This QA shows the spectral vs. spatial positions of all the lines traced by the code. Here is an example from shane_kast_red:

../figures/arc_tilts_2d.png

Here is what you hope to see in this QA:

  • RMS < 0.1
  • Very few red points
  • The red points are mainly at the very edges of the black lines
  • The black points span across the full detector

On the last point, if only a smaller portion of the detector is covered, the code is extrapolating. Indeed, the example above only shows outputs down to ~480 Spectral Pixel, which is not ideal. Of course, this will be the case for spectrographs that have data which does not span the full detector.

Spat Tilts

This QA examines the residuals of (tilt position - model) as a function of spatial offset along the slit. Here is an example from shane_kast_red:

../figures/arc_tilts_spat.png

One hopes to see small residuals without any substantial spatial dependence. But, it is common for there to be significant residuals at the edges of the slit (as in this example).

Spec Tilts

This QA examines the residuals of (tilt position - model) as a function of spetral offset along the slit. Here is an example from shane_kast_red:

../figures/arc_tilts_spec.png

One hopes to see:

  • The black points scattering about 0
  • The orange and green points not too far above 0

Troubleshooting

If one or more of your image appears to be in err, here are the things to consider:

Insufficient Lines

.. todo::

    Explain how to add more

Current WaveTilts Data Model

Internally, the image is held in :class:`pypeit.wavetilts.WaveTilts` which subclasses from :class:`pypeit.datamodel.DataContainer`.

The datamodel written to disk is:

TILTS content is: