APT Aladin Viewer
The JWST Aladin visualization tool has been integrated into APT to allow users to visualize their observations onto the celestial sphere.
The Aladin Visualization tool is software from the Centre de Données astronomiques de Strasbourg that has been integrated into APT to assist users with visualizing their proposed observations onto various sky views such as the Palomar Digitized Sky Survey, 2MASS, Galex, SDSS, or a number of other selectable options. The Aladin tool is accessed in APT by selecting one or more visits or observations in the tree editor on the left side of the APT GUI and selecting the View in Aladin* icon on the APT top tool menu bar. The APT GUI changes to show Aladin control options and a separate window opens to show the visualization. Users can move back and forth between the form editor and the APT Aladin control panel as needed to change what is being displayed, but the visualization display window stays open until closed by the user.
Hint: after opening the View in Aladin tool and selecting an observation, click the Load DSS box in the APT Aladin control window to see the background image in the Aladin display window. If a different sky survey is desired for the display, the options are selected directly from within the Aladin display window
Note: The target shown in the Aladin display does not update automatically when observations or visits from a different target are selected in the APT tree editor. The user must click the Load DSS box in the APT Aladin control window to force display of the new target.
Our goal here is not to provide a complete overview of this tool, but rather highlight a few aspects that should be most useful to proposers. The implementation in APT is largely the same for the HST and JWST branches of APT, but there are aspects that are specific to one or the other branches. Video training help is available and recommended for learning some of the ins and outs of Aladin, but many features are intuitive. You are encouraged to play around with the many options provided by the Aladin tool itself and the APT interface to it.
The APT Aladin control window in the APT GUI contains a number of helpful features that can be turned on and off as desired, depending on the application (see Figure 2). The Load DSS box has already been mentioned, but a few others of special interest include:
- FoV button: toggles the entire set of JWST instrument footprints, showing the the entire JWST focal plane. Of course, unless the position angle of the selected observation or visit has been set, this is just provisional. But if the position angle has been fixed (or a range provided), this display will show the actual expected relative positions of the different instrument FoVs with respect to the selected visit or observation.
- Orient Ranges button: When a position angle or range HAS been set on a given observation, this display is useful for showing the allowed range of motion for the reference angle of the selected instrument. A circle is displayed, where the green portion indicates the allowed PA range and the red portion shows disallowed ranges.
- Coverage Circles button: this display simply shows what happens when the selected field of view is rotated on the sky. So for example, if an imaging mosaic has been specified, but the position angle has not been restricted, this display shows the full area that in principle might be within the filed of view at the time of the observation.
- Grid button: simply displays a coordinate grip over the Aladin display.
- Single Aperture button: (Added APT 25.1.1) For certain modes (mainly NIRCam), this toggles to a simplified view of the field overlay.
- JWST GS box (next to Load DSS box):
Figure 3 shows the Aladin display resulting from selecting a few of these options for a particular example. The display of the JWST instrument fields of view for each elected template mode have undergone a major upgrade as of APT 25.1.1 release in June 2017.
Interactions between Aladin and APT
One of the most useful interactions between the Aladin display and APT is the ability rotate or move a displayed JWST field of view by grabbing it with the cursor. These manual adjustments show up in the APT Aladin GUI, as shown in Figure 3. If you decide to keep the indicated change, you can either commit a particular selected change or commit all listed changes back into your proposal by electing the appropriate button on the left side of the APT Aladin control window.
A word of caution regarding position angle changes: Aladin will allow you to rotate a given field of view through the entire 360o range, but this does not mean that all angles are necessarily allowed for JWST observations of a particular target. It is only by running the visit planner with a given position angle (or range) specified that actual schedulability can be verified.
If a mosaic observation is displayed, grabbing a tile and rotating it to a new position angle is followed very shortly be a repositioning of the entire mosaic pattern in the display. This is a result of the way mosaic observations are defined. See the APT Mosaics article for more information.
Aladin visualization tool information
Aladin Desktop & Aladin Lite are developed by the Centre de Données astronomiques de Strasbourg.
Both are distributed under GPL v3 licence.
If the Aladin Sky Atlas was helpful for your research work, the following citation would be appreciated: This research has made use of "Aladin sky atlas" developed at CDS, Strasbourg Observatory, France → 2000A&AS..143...33B and 2014ASPC..485..277B.