Image Servers

Image servers differ from other types of ACL server in that they return a direct image or `pixel map' of a region of sky rather than a catalogue of objects. The image is returned formatted as a FITS file which may optionally be compressed.

1. Image servers have a configuration file entry similar to those for other types of database. The server type is imagesvr. The region of sky required is specified by giving the central Right Ascension and Declination (or $x,y$ pixel position if celestial coordinates are not available), width and height. The usual tokens (see Section ):

    %ra %dec %x %y %w %h

   are included in a query string as part of a url keyword in the usual fashion. The tokens have their usual meaning and units. An example configuration file entry for an image server is:

   serv_type:      imagesvr
   long_name:      Digitized Sky at ESO
   short_name:     dss@eso
   url:            http://archive.eso.org/dss/dss\
   ?ra=%ra&dec=%dec&mime-type=%mime-type&x=%w&y=%h
   copyright:      Digitized Sky Survey (c) by AURA, provided online by ESO
   

2. The server parses the query and generates a FITS file corresponding to the region specified. It first returns the MIME type, followed by the FITS file which optionally may be compressed. The MIME types corresponding to the various types of compression are listed in Table . For example, the MIME type for a gzipped FITS file is:

   Content-type: image/x-gfits

Table: MIME types for compressed FITS images

MIME type	Type of compression
image/fits	uncompressed
image/x-hfits	H compressed
image/x-gfits	gzipped
image/x-gstarbase	gzipped (alternative)
image/x-cfits	UNIX compressed
image/x-cstarbase	UNIX compressed (alternative)
text/html	error message in HTML format