Change page style: 

Position Editor Menu Bar

The position editor menu bar is used to configure the image and overlay displays:

  • File - open, save and print images (see details below).
  • View - configure and examine the image properties (including cut levels, colour table and FITS header; see below); configure the offset and WFS displays (see details below).
  • Go - navigate the image history list
  • Graphics - annotate the image with text and graphics. These can be saved with the underlying image
  • Catalog - access on-line source catalogs (including guide star), imager servers (including sky survey), archives and personal catalogs, configure the display of catalog overlays and access the catalog navigator. The overlays can be saved with the underlying image.

Further information about the highlighted functions see below.

Open, Save and Print Images

Any simple FITS image may be loaded into the position editor. If the image has multiple planes, a summary of the image extensions is reported and you can choose which extension to display.

The raw image can be saved to a FITS file or in one of several file formats (e.g. jpeg, tiff, bitmap) from the file save as menu. You can save any graphics (overlays, annotations) as an extension in the FITS file using the graphics save graphics with image menu. Likewise you can save catalogs in a FITS extension using the catalog overlays with image menu. This FITS file may be loaded into the position editor at a later time, the image displayed and extensions selected and displayed using the manipulation tools.

Alternatively, and more portably, you can save the overlays along with the image in jpeg or gif formats from the file save current view menu. This format is particularly useful if you have annotated the image e.g., as a finding chart.

The image with overlays can be printed, and previewed, directly from within the position editor or by printing an image saved to disk.

To close the position editor select file close or click on the X in the upper right corner.

Image Examination and Manipulation

You can interactively change the high and low cut levels either manually, by selecting the percentile range or the median clipped range from the view cut levels menu.

You can change the colour table, intensity transformation and mapping algorithm from and view colors menu.

The view fits extensions menu shows the various data structures contained in the FITS file. This may simply be the image plane or may include header and data extensions. If you have used the position editor to save an image with a catalog then select the appropriate FITS table extension name and click open. This opens the catalog navigator from which you can plot (or unplot) the catalogued objects.

The keywords, values and comments in the current FITS header are displayed with the view fits keywords menu.

Configure the Offset Display

The view base position offset display menu configures how the offset iterator sequence is displayed. You can toggle the tags (steps in the offset list) on/off, and display the science field of view at the selected, all or none of the offset positions.

Configure the OIWFS FOV Display

From the view OIWFS FOV display menu you can choose whether to display the on-instrument wavefront sensor vignetting region in outline or solid block of colour. If the OIWFS is not in the focal plane (e.g. NIRI) you can choose whether to include or exclude the partially vignetted region.

History List

The position editor maintains a history list of images displayed. You can navigate forwards or backwards through the list, jump to a particular image, or clear the history list from items in the Go menu.

Access / Display On-line Catalogs and the Catalog Navigator

Several data centres maintain object catalogs and image servers that can be interrogated remotely. The position editor contains a powerful catalog navigator for downloading an image of the field around the science target plus the co-ordinates and other properties of objects within this field. This is particularly useful when laying out the telescope offset pattern and when selecting guide stars.

caution The primary data servers are at STScI, CADC, ESO and 2MASS.

Select one of the catalog image servers (e.g,. Digitized Sky at ESO) and an image is returned of the field around the base telescope position for the currently selected observation in the science program.  A dot to the left of a catalog name means that this catalog was the last one queried and is the catalog that will be used when the Images quick download button on the Position Editor toolbar is pressed. Selecting a new catalog from this menu will change this default.

Next, select one of the guide star catalogs (e.g., catalogs UCAC2 Catalog at CADC) and a list of stars within the field is downloaded; these are overlayed on the image using the catalog button. Selecting the catalogs browse menu opens the catalog navigator which shows the search criteria that were used and the query results:

catalogue navigator

You can plot and unplot the objects in this catalog from the buttons along the bottom of the catalog navigator. From the catalog navigator's configure button you can change the symbol displayed for each object and scale the symbol size depending on some property of the object (see the elliptical overlays in the catalog GSC-2 Gemini (ellipses) as an example, if available).

Additional catalogs such as RC3, ZCAT, and IRAS, etc. can be queried by selecting the catalog in the Skycat Catalogs folder in the catalog tree window.

It is possible to query several catalogs (separately) and overlay their results. (Unplot all is useful if you have opened several catalogs and the display is getting crowded!). The back and forward buttons on the toolbar take you through previous catalog search results.

With the position editor viewer in browse mode, click on one of the cataloged objects in the image and the relevant row in the query results list is highlight. You can also do the reverse and click on a row and the object is highlighted.

You can also change the query parameters (e.g. RA, dec, radii limits, brightness range) or object name (using the SIMBAD or NED name resolvers) and launch a new search from the Go button.

As with the image saving, loading and history features described above and available from the position editor menu bar, the catalog navigator menu bar offers the same capabilities for catalog objects.

Personal Catalogs

In addition to the on-line catalogs, you can overlay your own cataloged objects on the image. To study the require formats, e.g., the skycat style of tab-separated columns, it is useful to save and examine a downloaded catalog using the catalog navigator's file save as menu.