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- Goddard Utilities (`pydl.goddard`)

# Goddard Utilities (`pydl.goddard`)

## Introduction

This package provides functionality similar to the The IDL® Astronomy User’s Libary, sometimes called the “Goddard Utilities”, maintained by Wayne Landsman and distributed with idlutils.

In general, functions that are needed by `pydl.pydlutils` or `pydl.pydlspec2d` are implemented, while functions that are not needed have much lower priority.

The Goddard package is itself divided into a number of subpackages. Below we list the subpackages and the usability of the PyDL equivalent. The readiness levels are defined as:

Obsolete

  No point in implementing because the purpose of the code lapsed many years ago.

Not Applicable (NA)

  No point in implementing because another built-in or numpy/scipy/astropy package completely replaces this.

None

  Not (yet) implemented at all.

Rudimentary

  Only a few functions are implemented.

Fair

  Enough functions are implemented to be useful, but some are missing.

Good

  Pretty much anything you could do with the Goddard code you can do with the equivalent here.

Subpackage | Readiness Level | Comments
--- | --- | ---
astro | Rudimentary | General astronomical utility functions.
astrom | NA | Tools for manipulating WCS data in FITS headers. Use `astropy.io.fits` and `astropy.wcs`.
coyote | NA | The Coyote library for plotting and graphics developed by David Fanning.
database | None | Allows access to IDL-specific databases.
disk_io | None | Provides access to IRAF image (`.imh`) files and AJ/ApJ-style tables.
fits | NA | Use `astropy.io.fits`.
fits_bintable | NA | Use `astropy.io.fits`.
fits_table | NA | Use `astropy.io.fits`.
idlphot | None | Adapted from an early version of DAOPHOT.
image | None | Generic image processing functions, including convolution/deconvolution.
jhuapl | None | Functions from the JHU Applied Physics Lab.
markwardt | None | Levenberg-Marquardt least-squares minimization.
math | Rudimentary | Generic mathematical functions. Many are implemented in numpy or scipy.
misc | Rudimentary | General utility functions that do not involve astronomy specifically.
plot | NA | Functions that supplement the built-in IDL plotting capabilities.
robust | None | Robust statistical fitting procedures.
sdas | None | Provides access to STDAS/GEIS image files.
sockets | NA | Functions for performing web queries in IDL. Use astroquery.
structure | NA | Tools for manipulating IDL data structures. Use `numpy.recarray`.
tv | NA | Functions for manipulating IDL image displays.

## API

### pydl.goddard Package

This subpackage contains the Goddard utilities.

### pydl.goddard.astro Module

This module corresponds to the goddard/astro directory in idlutils.

#### Functions

`airtovac`(air) | Convert air wavelengths to wavelengths in vacuum.
`gcirc`(ra1, dec1, ra2, dec2[, units]) | Computes rigorous great circle arc distances.
`get_juldate`([seconds]) | Returns the current Julian date.
`get_juldate_main`() | Entry point for the get_juldate command-line script.
`vactoair`(vacuum) | Convert vacuum wavelengths to wavelengths in air.

### pydl.goddard.math Module

This module corresponds to the goddard/math directory in idlutils.

#### Functions

`flegendre`(x, m) | Compute the first `m` Legendre polynomials.

### pydl.goddard.misc Module

This module corresponds to the goddard/misc directory in idlutils.

#### Functions

`cirrange`(ang[, radians]) | Convert an angle larger than 360 degrees to one less than 360 degrees.