Create NDFs holding the map made form a short chunk of data SHORTMAP
"
shortmap"
adjacent time slices. Alternatively, set to -1 to
produce a map each time the TCS_INDEX value within the JCMTSTATE extension is incremented (i.e.,
each time a full pass through the scan pattern has been completed). Any other negative value is
interpreted as a duration in seconds, and is converted to time slices using the (possibly
down-sampled) sample frequency of the data being mapped. [0]