APT Aladin Viewer

The JWST Aladin visualization tool has been integrated into APT to allow users to visualize their observations onto the celestial sphere.

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Brief overview 

  Aladin Overview in APT Video Tutorial,   Using Aladin and APT Visit Planner Video Tutorial

Words in bold italics are buttons 
or parameters in GUI tools. Bold 
style represents GUI menus/
panels & data software packages.

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.
Figure 1. The screen view after opening Aladin and display the DSS image for a particular visit from a mosaic of M82.

The screen view showing the APT Aladin control panel at left and the Aladin display window at right. The windows are separate and can be moved and resized independently. The Load DSS box is highlighted at left, and the background display options are highlighted in the right panel.

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. 

Figure 2. The APT Aladin Control window showing several of the features described in the article

In this example, the FoV, Orient Ranges, and Grid buttons have been selected for a single visit. (The BOT Data button is also grayed out, but for a different reason:The Hubble Bright Object Tool is not relevant for JWST.) The results of these choices are shown in Figure 3. Note that a potential change in position of the selected visit has been made in the display, resulting in the red information in the Pending Changed GUI. This change will not be saved unless you use one of the "Commit" buttons at left, in which case the change is fed back into this target in the proposal.
Figure 3. The Aladin display window showing several of the features described in the article

The results of the choices shown in Figure 2 can be seen in this figure. The positions of other JWST instrument FoVs (gray boxes) can be seen relative to the selected NIRCam visit (shown in blue). A coordinate grid is overlaid on the display. The green portion of the circle shows that an orient range has been selected for this visit. The display is shown at the midpoint of the range. There are many Aladin display controls along the right side of the image window that are not described here.

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 360° 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.

Latest updates

  • Added revised video help links.

    Updated for APT 27.1 release, including figures

    Added links to three new Aladin tutorial videos

  • Figures 2 and 3 updated to APT 25.4.1.
Originally published