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).
FITS keyword: CENT_WST
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.
FITS keyword: R_BOUND
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.