It is important to have accurate coordinates (and accurate relative positions of potential guide stars, if appropriate) for each target or observation. Object coordinates are nominally placed in the PTL file (and get pulled forward into the MTL file), where columns for indicating the accuracy of the coordinate and a reference for the coordinate are also provided. Separate entries in the sequence database files track the coordinates listed on the SCIPLAN and those entered by science planners to assist in the process of checking. However, there are a number of reasons why coordinates may need to be updated at a later stage in the process. For instance, if the coordinate supplied for the PTL was only accurate to 30'', a better coordinate is needed for the actual observation (typically 1-2'' accuracy). Also, an extended target selected by UIT (which has a 40' field of view) may have a ``generic" coordinate in the PTL, and the spectrograph observers may choose a specific location for observation. Finally, it is desirable to have the best possible coordinate for any moving targets such as planets or comets, and these are often put in after the SCIPLAN is completed. Whatever the case, selecting, measuring, and/or verifying the coordinates and accuracies is an important step of planning, done shortly after the SCIPLAN is available.
Likewise, if any extended targets require specific roll angles, say to place a rectangular HUT aperture along the major axis of an elliptical galaxy, this needs to be determined and requested so that the orbital analysis engineers at MSFC can find appropriate guide stars for the IPS. Again, there are entries for setting a ``roll requested" flag and desired roll angle in the MTL file, and the same information needs to get propagated to the sequence database files. However, final decisions on some targets are not made until they are actually planned into the SCIPLAN, so an iteration and verification is usually needed.