Note -- need to clean up HTML encoded entities.  -- Joe

== Target Location ==

Target location, by which is meant the spatial location of the target
region of imaged or pointed observations on or around the Sun or in
the heliosphere, has not yet been built into any VSO query models,
although it is a fairly natural selection criterion for observations
with a restricted field of view.  It may suffice to specify a simple
uniform description, although the multi-dimensionality of space makes
this harder than one for time.  For two-dimensional image data we assume
a bounding circle as the simplest model.  For this model it is sufficient
to specify the center location and radius of the bounding circle.
Most real image data are actually described by a bounding rectangle,
but this requires specifying at least five parameters (''e.g.''
the coordinates of opposite corners and a position angle).  


==== Observation_Center_West ====


  type: ''number''[[BR]]
  unit: ''arc-second''[[BR]]
  FITS keyword: ''CENT_WST''

==== Observation_Center_North ====


  type: ''number''[[BR]]
  unit: ''arc-second''[[BR]]
  FITS keyword: ''CENT_NRT''

  A pair of coordinates specifying the location of the center of the
image data circle with respect to the Earth-Sun line at the nominal
Observation_Time.  This origin is close to the center of
the apparent solar image for Earth-based or near-Earth observers, but
not necessarily for deep space observations.  The North coordinate
is measured in the direction of the Carrington axis (RA 286 °13,
δ 63°.87 J2000.0), and the West coordinate in the direction
of solar rotation.


==== Bounding_Radius ====


  type: ''number''[[BR]]
  unit: ''arc-second''[[BR]]
  FITS keyword: ''R_BOUND''[[BR]]

  The radius of the bounding circle about the Observation_Center.
For the VSO Data Model the bounding circle is to be understood as either
the maximum inscribed circle in the bounding data rectangle (polygon),
or the minimum circumscribed circle, depending on whether the query is
for included data (presumably the normal default) or excluded data,
respectively.