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Interactive examination of data

The user can interact with a displayed image or plot by use of either:

• CURSOR is used for both images and lists. The values of data points can be read and stored in a CLIST list slot. The actual position recorded by the cursor can optionally be modified using one of two centroiding algorithms /FIT finds a local centre of mass and /GFIT fits a 2D gaussian. This could be used in identifying targets, which would then have to be TRANSFORMed into a MASK list.

  If a PLOT is being examined there is the option to edit the corresponding list by means of the /EDIT qualifier. This is particularly useful for BOXES and MASK lists, which can be modified to change the size and position of the boxes in addition to deleting entries altogether. Both lists are required so that the information in each remains correlated. Care should also be taken with this routine as it works on proximity to bottom, left-hand corner of the box rather than simply seeing which box the cursor is currently in.

  The particular options, corresponding to the keyboard numeric buttons, are displayed on the terminal.

  The option CURSOR/FC allows the field centre to be respecified.

• BROWSE can also be used to examine either DISPLAYed images or PLOTed lists.

  In image mode the each cursor read results in the position and value of the pixel to be output. Also, if a BOXES list is available then the box number which the pixel occupies is also output, whilst, if COEFS are present, the wavelength corresponding to the position is reported.

  In list mode the cursor read causes the list to be examined and the number of the closest list element to be reported.

  In both cases the cursor position is read on each button depression, and a position selected outside the display area brings about the exit.