||<-3 tablestyle="width:92%" style="border-style: none; text-align: center"> {{attachment:ADASS01.gif||height=430}} ||

= Developments in the Starlink AST library - an intelligent WCS management system =

||<-3 tablestyle="width:92%" style="border-style: none; text-align: center"> http://www.starlink.ac.uk/ast/  ||
||<tablestyle="width:92%" style="border-style: none">David S. Berry,<<BR>> Centre for Astrophysics,<<BR>> University of Central Lancashire,<<BR>>Preston, Lancs. UK.<<BR>> PR1 2HE.<<BR>>[[mailto:dsb@ast.man.ac.uk|dsb@ast.man.ac.uk]]<<BR>> Tel. 01772 893564 ||<style="border-style: none; text-align: center"> {{attachment:ADASS02.gif||height=166}}||<style="border-style: none">funded by:<<BR>> The Starlink Project,<<BR>> Rutherford Appleton Laboratory,<<BR>> Didcot, Oxfordshire, UK.<<BR>> OX11 0QX<<BR>> [[mailto:ussc@star.rl.ac.uk|ussc@star.rl.ac.uk]]<<BR>> http://www.starlink.ac.uk/ ||

'''Contents:'''

  1. [[#A|The Starlink AST library]]
  1. [[#B|What's new in AST]]
  1. [[#C|Coming soon]]
  1. [[#D|Support within AST V3.0 for FITS-WCS features and keywords]]
  1. [[#E|AST in use]]

<<Anchor(A)>>
== The Starlink AST library: ==

Provides a comprehensive range of facilities for attaching world coordinate systems to astronomical data, for retrieving and interpreting that information and for generating graphical output such as coordinate grids based upon it.

Can read and write WCS information stored in the form of FITS-WCS headers, but also provides its own richer format.

Object-oriented design implemented in pure ANSI C with interfaces for C, FORTRAN and Java (''via ''JNI).

Has built-in intelligence for identifying flavours of celestial, spectral and other coordinate systems and determining how to transform between them, allowing general purpose code to be written which makes no assumptions about the nature of the coordinate systems.

Includes a flexible and versatile “tool-kit” for creating and modifying collections of coordinate frames interconnected by arbitrarily complex transformations.

Easy-to-use graphical facilities allow the production of annotated grids such as those in the montage above. Graphics are draw ''via'' a simple “driver” module which AST calls to draw lines, strings, markers, ''etc''. AST includes a driver for PGPLOT; drivers for other graphics systems (''e.g. ''Tcl/Tk, Java/Swing, ''etc.'') can easily be (and have been) written. An [[example_code.html| example of code]] which draws a coordinate grid is shown on this poster.


<<Anchor(B)>>
== What’s new in AST: ==


=== V2.0 (highlights only): ===


A new class called !SpecFrame has been added which represents positions within an electro-magnetic spectrum. A !SpecFrame can converts spectral axis values between any of the coordinate systems or rest frames listed in FITS-WCS paper III, using any appropriate units.

The !astConvert method, which automatically finds a Mapping between any two coordinate Frames, now takes account of the “Units” string in the two Frames, so long as they use the conventions for described units included in FITS-WCS paper I.

=== V3.0 (highlights only): ===

Support for FITS-WCS papers I, II, III & IV has been extended significantly. The current status is shown in the two tables to the right.

Includes new documentation giving the details of AST’s implementation of FITS-WCS papers I, II and III.

The !SkyFrame class (which represents coordinate systems on the sky) now supports ICRS and helio-ecliptic coords.

The Mapping class (which represents coordinate transformations) has a new method to determine the rate of change of any Mapping output with respect to any Mapping input.

Several new sub-class of Mapping have been added:

'''!PolyMap''': Performs a general N-dimensional polynomial transformation.

'''!GrismMap''': Models the dispersion in a grism or prism.

'''!ShiftMap''': Shifts each axis by a specified constant.

Simplification of complex Mappings has been extended.

<<Anchor(C)>>
== Coming soon: ==

  * New XML formats for WCS information, including IVOA Space-Time-Coordinate format.
  * Support for coordinate systems representing time, including automatic identification and conversion between different temporal systems.
  * Increased coverage of FITS-WCS papers.

<<Anchor(D)>>
== Support within AST V3.0 for FITS-WCS features and keywords: ==

|| '''Feature:''' || '''Status:''' ||
|| Axis distortions (as described in paper IV) || Ignored (except for the SIRTF-specific “-SIP” code which is interpreted correctly when reading a FITS header, but is never written out to a new FITS header). ||
|| Alternate axis descriptions || Supported ||
|| User-defined fiducial points || Supported ||
|| Choice of PC''i_ja'' or CD''i_ja ''matrix || Supported ||
|| Deprecated WCS conventions (e.g. keyword CROTA''i'', EPOCH, PC''iiijjj, ''the NCP projection,'' etc.'') || Supported ||
|| Alternate keyword formats for inclusion in tables || Unsupported ||
|| Units in comment strings || Unsupported ||
|| Uncertainties in the coordinates || Unsupported ||
|| “WCSDEP” convention || Unsupported ||
|| Use of longitude projection parameters to store LONPOLE and LATPOLE || Supported ||
|| Common, non-standard features || Support for reading (but not writing) various common, non-standard feature such as “TNX” and “ZPX” projections is included. More can easily be added as requested. ||

<<BR>>

<<BR>>


||'''Keyword:''' || '''Description:''' || '''Status:''' ||
|| WCSAXES''a'' || WCS dimensionality || Supported ||
|| CRVAL''ia'' || Value at reference point || Supported ||
|| CRPIX''ja'' || Pixel of reference point || Supported ||
|| CDELT''ia'' || Increment at reference point || Supported ||
|| CROTA''i'' || Rotation at reference point || Supported (only written when producing a “FITS-AIPS” header) ||
|| CTYPE''ia'' || Coordinate/algorithm/distortion type || Supported (all coordinate systems [including helio-ecliptic] and algorithm codes listed in papers I, II and III, with the exception of the “STOKES” and “COMPLEX” values defined in paper I, the “CUBEFACE” value defined in paper II, and the “-TAB” algorithm defined in paper III) ||
|| CUNIT''ia'' || Units of coordinate values || Supported (including automatic unit conversion if the units strings conform to paper I conventions) ||
|| PC''i_ja'' || Transformation matrix || Supported ||
|| CD''i_ja'' || Transformation matrix || Supported ||
|| PV''i_ma'' || Algorithm numerical parameter ''m'' || Supported ||
|| PS''i_ma'' || Algorithm textual parameter ''m'' || Unsupported ||
|| WCSNAME''a'' || Coordinate version name || Supported ||
|| CRDER''ia'' || Random error || Unsupported ||
|| CSYER''ia'' || Systematic error || Unsupported ||
|| LONPOLE''a'' || Coordinate rotation (celestial axes) || Supported ||
|| LATPOLE''a'' || Coordinate rotation (celestial axes) || Supported ||
|| RADESYS''a'' || Frame of reference (celestial axes) || Supported (all systems, except ecliptic coordinates are currently assumed to be FK5) ||
|| EQUINOX''a'' || Coordinate epoch (celestial axes) || Supported ||
|| EPOCH || Coordinate epoch (celestial axes) || Supported (only written when producing a “FITS-AIPS” header) ||
|| MJD-OBS || Time of observation || Supported ||
|| SPECSYS''a'' || Spectral reference frame || Supported (all systems, except CMBDIPOL) ||
|| SSYSOBS''a'' || Spectral reference frame fixed during observation || Unsupported ||
|| OBSGEO-X/Y/Z || Observation position || Supported ||
|| MJD-AVG || Average date of observation || Supported ||
|| VSOURCE''a'' || Physical velocity of source for SPECSYS=SOURCE cases || Supported ||
|| ZSOURCE''a'' || Optical velocity of source for SPECSYS=SOURCE cases || Supported ||
|| VELOSYS''a'' || Velocity w.r.t. standard of rest || Unsupported ||
|| RESTFRQ''a'' || Line rest frequency || Supported ||
|| RESTWAV''a'' || Line rest wavelength in vacuum || Supported ||
|| CNAME''ia'' || Descriptive axis label || Supported ||

<<BR>>

<<Anchor(E)>>
== AST in use: ==


 * The '''[[http://hea-www.harvard.edu/RD/ds9/|DS9]]''' image browser is a Tcl/Tk/C++ application which uses AST to produce its coordinate grids:

<<BR>>

{{attachment:ADASS01.jpg}}

<<BR>>

 * '''[[http://www.starlink.ac.uk/splat/|SPLAT]] '''(a spectral analysis tool produced by Starlink) is written in Java and uses AST for its graphics and WCS handling.

<<BR>>

{{attachment:ADASS3.gif}}

<<BR>>

 * '''[[http://www.starlink.ac.uk/gaia/|GAIA]]''' is another image browser written in Tcl/Tk/C++ which uses AST.

<<BR>>

{{attachment:ADASS03.jpg}}