Tpoint Formulas

This is taken verbatim from the Tpoint (TM) manual by Patrick Wallace.

Here I describe the formulas that are related to the pointing model implemented in schierd for the ROTSE-III telescope. This is for quick reference only, and details can be found in the Tpoint manual.

• ID                 Index Error in Declination

  Declination index error in an equatorial mount: the zero-point in ${\delta}$.

  ${\Delta \delta = + {\tt ID}}$

• IH                 Index Error in Hour Angle

  Hour angle index error in an equatorial mount: the zero-point of ${h}$.

  ${\Delta h = + {\tt IH}}$

• NP                 HA/Dec Non-perpendicularity

  In an equatorial mount, if the polar axis and declination axis are not exactly at right angles, east-west shifts of the image occur that are proportional to ${\sin \delta}$.

  ${\Delta h \simeq + {\tt NP} \tan \delta}$

• CH                 East-West Collimation Error

  In an equatorial mount, the collimation error is the non-perpendicularity between the nominated pointing direction and the declination axis. It produces an east-west shift that is constant for all declinations.

  ${\Delta h \simeq + {\tt CH} \sec \delta}$

• ME                 Polar Axis Misalignment in Elevation

  Vertical misalignment of the polar axis of an equatorial mount: a rotation about an east-west axis equal to coefficient ME.

  ${\Delta h \simeq + {\tt ME} \sin h \tan \delta}$

  ${\Delta \delta \simeq + {\tt ME} \cos h}$

• MA                 Polar Axis Misalignment in Azimuth

  Misalignment of the polar axis of an equatorial mount to the left or right of the true pole: a rotation about an axis through ( ${h = \delta = 0}$) equal to coefficient MA.

  ${\Delta h \simeq - {\tt MA} \cos h \tan \delta}$

  ${\Delta \delta \simeq + {\tt MA} \sin h}$