The “Rectangular Grid Inputs” portion of the GUI includes all the fields that the observer should need to specify in order to get the telescope to move in a rectangular pattern centered on the Home position. The position that the operator slews the telescope to and that is considered to have offsets of 0”, 0” is the Home position. In a 3x3 grid the Home position will be position 5 in the grid, however, in a rectangular grid with an even number for either of the RA or DEC dimensions the Home position will not be one of the positions of the grid. Therefore, if a standard is being observed in a 2x2 grid the center of the standard field will never be on the center of the array unless the telescope is offset before starting the grid pattern. (Note: You may therefore only want to do odd-numbered grid patterns (e.g. 3x3, 5x9). But you are allowed to do even numbered grid patterns as well!) The positions included in the grid will be moved to using a “snake” pattern, a back and forth sequence, which enables the telescope to move to each subsequent position by offsetting in only one axis rather than two.
N.B. For any rectangular grid, the first click of the forward button will move the telescope from the Home position to the North-East corner of the rectangular grid.
This was created as a simple default offset pattern that could be used by observers to cover any object. The grid can have overlapping positions (if the offsets specified are smaller than the field of view of the instrument), adjacent positions (if the offsets specified match the field of view of the instrument) or widely separate positions (if the offsets are larger than the field of view of the instrument). The offsets in RA and DEC do not have to be the same and neither do the dimensions.