  The Vector Spectromagnetograph (VSM) instrument on the Synoptic Optical
Longterm Investigations of the Sun (SOLIS) telescope is capable of obtaining
spectropolarimetry for the full Sun (or a select latitudinal range) with one
arcsecond spatial resolution and 0.05 Angstrom spectral resolution. This is
achieved by scanning the Sun in declination and building up spectral cubes for
multiple polarization states, utilizing a beamsplitter and two separate 2k x 2k
CCD cameras. As a result, the eastern and western hemispheres of the Sun are
separated in preliminary VSM images by a vertical gap with soft edges and
variable position and width. Prior to the comprehensive analysis presented in
this document, a trial-and-error approach to removing the gap had yielded an
algorithm that was inconsistent, undocumented, and responsible for incorrectly
eliminating too many image columns. Here we describe, in detail, the basis for
a new, streamlined, and properly calibrated prescription for locating and
removing the gap that is correct to within approximately one arcsecond (one
column).
