Image Link Setup dialog box (Tools Image Link)

Use this dialog box to specify options for pasting images on the Virtual Sky. Images are pasted during an Image Link, or when an image retrieved from the Digitized Sky Survey.

Image Display Options Group

Use the options in this group to specify how the image is displayed.

Transparent or Opaque

Once the image has been created and superimposed on the Virtual Sky, there are two ways the image can interact with the Virtual Sky.

The Transparent option combines the image with the Virtual Sky so that stars plotted by TheSky "show through" stars on the actual image as black dots. In this way, you can quickly identify star-for-star matches and verify that the image’s position is correct.

When the Opaque option is selected, the image is plotted on the Virtual Sky first. All other Virtual Sky elements that are plotted (coordinate grid lines, non-stellar objects, or extended labels, for example) are drawn on top of the actual image. Stars are not plotted by TheSky when the Opaque option is selected.

The Opaque option gives you great flexibility as to how an image is displayed on the Virtual Sky. Images can be shown with no stars or other screen elements plotted, or they can be shown with star names, objects magnitudes, coordinate grids, galaxy outlines or any other Virtual Sky elements turned on.

Image Size (% of Virtual Sky)

Enter a percentage value (20-100) that indicates how much of the Virtual Sky is filled with a DSS image. This allows you to view a relatively large field of view in the Virtual Sky, yet retrieve an image that covers a smaller area in the center of the display.

Image is Linked

When is option is checked, TheSky "remembers" the coordinates of the current image and the coordinates of the center of the Virtual Sky. If you move to a different location in the sky (by zooming or scrolling), the image is automatically hidden from view. When you return to the same coordinates as the linked image, it is displayed normally.

There are two ways to automatically link an image to the Virtual Sky. The first is to use the Link Wizard and have TheSky determine a match between the simulated sky and the actual image. The second way is to retrieve an image from the DSS. DSS images contain the necessary orientation information so that the Virtual Sky can be automatically linked to the image.

If the "Image is linked" option is unchecked, moving around the sky does not automatically hide or display the displayed image. In fact, no matter where you look in the sky, the image is displayed. To turn off the image, click the Display Image command on the Image Link menu under the Tools menu.

You can also fine-tune the position of a linked image by turning off the "Image is linked" option, adjusting the Virtual Sky, then turning this option back on to update the currently linked coordinates.

Search Parameters

Use the options in this group to specify the scale of the image.

Unknown Scale

Mark this option if the scale of your image (in arcseconds per pixel) is not known. TheSky will display the scale of the image in the Object Information dialog box after a successful Image Link is performed. Click the mouse anywhere inside the image to view this information.

Known Scale

Mark this option if the scale of your image is known. Enter this value, in arcseconds per pixel, in the text box.

Search Radius

Enter the radius of the area to search for a match between the image and the Virtual Sky.

Scale Tolerance

Enter the percentage of tolerance between the actual image scale and the Known Scale when performing an Image Link. For example, if you enter 2.0 for the Known Scale, and 10 for the Scale Tolerance, TheSky uses image scales between 1.8 and 2.2 when searching for matches between known stars and stars in the image.

Required Match Percentage

Enter a percentage that specifies the number of catalog stars (known stars) that must match the number of stars in the image.

Show Image Frame

Mark this option to draw a frame around the image.

Show Telescope Frame

Mark this option to draw a frame around the area that represents where the telescope is currently pointed.