When FITS files are dragged and dropped onto the Control window FITS files area, exposure boundary lines are added to the Screen Ruler window to indicate where each exposure starts and stops along the length of the Ruler. The date and time recorded in the FITS keywords within the FITS header of each file, together with the exposure duration are used to position the exposure boundaries.


The accurate placement of the Screen Ruler is covered in Tutorial III, but the accuracy of the placement of the exposure boundaries along the ruler is dependent on the accuracy of the time information stored in the FITS keywords and the correct configuration of the FITSDateType setting.


Exposure boundaries can be selected or unselected. Adjacent selected exposure boundaries are shown with alternating colours. Unselected exposure boundaries are shown with a single, separate colour. The width of the exposure boundaries can be configured, selected and unselected exposure boundaries can have different widths. The colours and line widths are configured in the Exposure Markings category of the Settings window.


Example


Screen Ruler window

Here 8 FITS images of a fast moving artificial satellite (34265U = 2009-010B) have been stacked together with zero motion, so that the stars appear as points but the moving object appears as 8 streaks as it moved from right to left through the field of view. Each exposure was 5.0 seconds duration and the object was moving at 14.7 arc seconds per second. The gaps between the end of one exposure and the start of the next can be seen to be uneven, with larger gaps between images 1 and 2 and between 6 and 7.


The Screen Ruler has been dragged from the mid-point of the first to the mid-point of the last streak, so the direction of motion is indicated by the arrow on the left end of the ruler. The Ruler has been positioned slightly below the streaks for clarity. The exposure boundaries appear as alternating blocks of red and aqua colour. The right hand end of each block equates to the exposure start time and the left hand end the exposure end time.



The Perpendicular line has been turned on by pressing F9 and the mouse moved to three positions to indicate the different information displayed in the mouse tooltip when positioned on or between exposure boundaries. The three sets of tooltip information have been superimposed.


Two of the perpendicular lines cross the exposure boundary coloured blocks for images 6 and 7. The associated mouse tooltips display the image sequence number and the underlying file name.


There is no file name to display at the mouse tooltip for the middle line, falling between the exposure boundaries for images 6 and 7. Instead an interpolated value for the image sequence number (6) is shown, assuming the exposures are evenly spaced from first to last. However, the time shown (21:07:00) accurately indicates the time when the object was at the crossing point of the perpendicular line and the Ruler.


Control window

Dropping the 8 FITS files on the Control window automatically selects all 8 in the file list, each line shows the sequential number, the exposure start time and the name of the FITS file.

Note that the Start and End image numbers are automatically set and the Start and End times are set from the time information contained in the FITS files:


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