Screen Ruler window


The Screen Ruler window is a resizeable, semi-transparent window that can be placed over other windows. It contains a moveable and resizeable line used as a ruler to read off measurements from underlying images. The parts of the Screen Ruler (on the left) are shown here, as well as the source of the Mouse information coming from the Control window on the right.


Ruler:

The ruler is a straight line that can be drawn on the semi-transparent window. There are a number of ways to draw the ruler or change its position:


  • Drag a fresh line by holding the left hand mouse button while moving the mouse
  • Set the starting point by positioning the mouse at the required place and:
    • pressing the Home key, or
    • pressing the Enter key, or
    • holding Shift and clicking the left mouse button
  • Set the ending point by positioning the mouse at the required place and:
    • pressing the End key, or
    • holding Ctrl and pressing the Enter key, or
    • holding Shift and clicking the right mouse button
  • Move the starting point when the ruler is unlocked by pressing the arrow keys
  • Move the ending point when the ruler is unlocked by holding Ctrl and pressing the arrow keys
  • Move the entire ruler when the ruler is locked by pressing the arrow keys
  • Move the Screen Ruler window by dragging the title bar with the mouse moves the Ruler along with the window
  • Hold Ctrl while moving the Screen Ruler window to leave the Ruler stationary


The ruler width and colour are adjustable from the Control window Settings area.


Image information can be entered into the Control window Settings area so that when the mouse hovers over the Screen Ruler window, information indicated by the mouse position is displayed as a tooltip next to the mouse cursor. The information always includes a sequential image number and can optionally include a time or a FITS file name if FITS files have been dropped on the Control window FITS files area. In the screen print above, the mouse position is used to interpolate between the start and end image numbers (1 and 10) and the start and end times (21:02:31 and 21:08:07) entered in the Control window to produce the tooltip information "8 @ 21:06:46", i.e. the nearest point on the ruler to the mouse position is at image number 8 and the estimated time for that position is 21:06:46.


The ruler can be temporarily hidden when moving the mouse over the Screen Ruler window by holding the Alt key.


Ruler arrowhead:

An optional arrowhead can be displayed at the end point of the ruler. See the Control window Show arrow? check box for details.


Extension line:

A thin white, dotted extension line extends either end of the ruler. This line is always displayed and is not adjustable. It is used to extrapolate the image number and optionally time from the mouse position when it is outside the limits of the ruler.


Perpendicular line:

Press the F9 key to toggle on or off the display of a thin yellow line from the mouse position, perpendicular to the ruler. This crosses the ruler at the closest point between ruler and mouse. Various actions use this crossing point rather than the actual mouse position, even if the perpendicular line is not displayed, such as:

  • the interpolated image number, time or FITS file name displayed in the mouse tooltip are calculated for the crossing point
  • when dragging the mouse while holding Shift+Ctrl or Ctrl to select or deselect FITS files, the files affected are determined from the crossing points at the start and end of the dragging operation. 


Ruler information:

The status area at the bottom of the Screen Ruler window shows the current x,y position of the mouse pointer and the start and end points of the Ruler. Coordinates start at (0,0) in the top left corner of the Screen Ruler window and increase downwards and to the right.

Also displayed is the position angle (P.A.°) of the Ruler, measured in degrees. This is the angle subtended by a vertical line with origin at the Ruler start point and the Ruler itself, increasing in an anticlockwise direction, which is the convention used by the Minor Planet Center, where North = 0° and East = 90°. If images are not perfectly aligned with North up an adjustment to correct the calculated P.A.° value can be manually entered in the Control window, or if FITS files containing the CROTA1 FITS keyword are dropped on the Control window it is automatically set. See Image Rotation °.

Created with the Personal Edition of HelpNDoc: Produce electronic books easily