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The Position Editor Viewer can display an image of the field an overlay it with information about the observation. It is not necessary to have a background image in orderto show the overlays. The overlays can be toggle and manipulated using the position editor buttons. The image can be manipulated using the view item on the menu bar.
Additional features of the viewer are:
- Zoom buttons (+,-) and current magnification shown on the lower status bar (also available in the position editor menu bar).
- Pixel coordinates and value for the current cursor position shown on the lower status bar.
- RA, dec and co-ordinate system (e.g. J2000) for the current cursor position derived from the image world co-ordinate system information.
- Pan and (fixed-magnification) zoomed windows show in the upper riight. The yellow box in the pan window shows the area currently displayed in the main window. Click-and-drag the yellow box to pan around the field at the current magnification. Display of the pan and magnifier window may be toggled using the hide button.
- Measure distances between two positions by right-clicking-and-dragging the cursor. The separations are given in arcmin:arcsec in both RA, dec axes and along the hypotenuse.
By default the image and overlays displayed correspond to the currectly selectedobservation in the science program. You can navigate through other, previously stored, images using the position editor toolbar (and get very confused!). A warning is shown in the viewer if the base (telescope pointing) position is outside of the displayed field.
Image Cache Details
The position editor viewer maintains a cache of 20 images. Whenever you select an observation in the science program, the software looks for an image in the cache whose center is close to the base position and displays it, if it is found. This means that if you move the base position a certain amount, the image in the cache will not be used any more.
The files in the cache directory correspond to the files in the image history menu (go item on the menu bar). The latest files are always shown at the top of the menu and when more than the maximum number (currently 20) is reached, the oldest image file is deleted and removed from the end of the menu.
The cache directory can be found at $HOME/.jsky/cache. Under windows $HOME is what ever is returned by java for the 'user-home' property. For Windows 2000, this is Documents andSettings\