The USVAO Data Discovery Tool User Guide

Version 1.4
October 2012



The USVAO Data Discovery Tool (DDT) is a web application for searching repositories of information about Astronomical Data, Publications and Images.

Fig. 1—Anatomy of the Data Discovery Tool as it appears prior to the first search. Circled numbers in orange are keyed to descriptions in the text.

The initial screen layout consists of the following components, numbered as in Fig. 1:

1. Search Box and other high-level tools
A hint appears describing the kind of query that should be performed. Also contains examples that populate the search box for you, a link to this guide and website information.
2. Data View Panel
Presents data and images returned from the query or queries, sometimes allowing multiple views of a dataset, such as a grid layout or an album view. If filtering is available for the data panel, applicable filters are grouped into facets by semantic type, and will appear in this panel. Note that the Filters panel can be resized or (un)hidden using screen widgets. The initial view of data panel shows a welcome page.
3. AstroView Panel
This panel may be optionally loaded by the tool. A Flash application, this powerful all-sky viewer provides visualization context and imagery for either aribtrary positions specified within the viewer itself or while being tied to data from DDT queries. Flash v10.2 is required to use AstroView.

Initiating a Search

All searches begin by entering either the name of an astronomical object, or the coordinates of a sky position in the search entry box in RA/Dec, sexagesimal or galactic coordinates (on the left in Fig. 2). The search can be initiated by clicking the Search button or by pressing the Return key on your keyboard while the cursor is in the search entry box.

Search Entry Box
Fig. 2—Search panel includes the Search box, radius selector, search button, and examples of valid search text.

Names of objects are passed to a name resolver (one of many Virtual Observatory services that support the DDT), which associates known object names with sky coordinates. A wide variety of catalog and common names can be resolved to known objects. Coordinates can be given in a variety of formats; right ascensions must be positive and southern declinations require a leading negative sign. Examples of valid names and coordinate formats are given below.

Object Names
M101, NGC45 Objects from standard catalogs such as Messier and NGC
Antennae, Eta Carinae Common names often work
T Tau Variable star names often work
BD+19 706 Star catalogs with coordinate symbols
png 000.8-07.6 Other catalogs with coordinate and decimal symbols
2MASS J04215943+1932063 All-sky catalogs with coordinate symbols
TYC 1272-470-1 All-sky satellite catalogs with restricted symbols
14 03 12.6 54 20 56.7 Sexagesimal coordinates delimited with spaces
14:03.210 54:20.945 Sexagesimal coordinates delimited with colons; decimal minutes/arcminutes
14h03m12.6s +54d20m56.7s Sexagesimal coordinates with explicit hms/dms
g102.0373+59.7711 Galactic coordinates of the form g[lon][+/-lat] with no spaces
180.468 -18.866 Coordinates in decimal degrees

Objects from standard catalogs such as Messier and NGC will be resolved. Common names often work. Further rules and caveats for valid searches may be found in Tips & Notes.

Exploring Search Results

A successful search, such as that shown for M57 in Fig. 3 below, populates a new Search Results panel with a table of resources, a corresponding Filters panel applicable to these resources, and focuses the AstroView component on the position. If the software detects image outlines (footprints), it will draw them, and will attempt to mark non-images, such as catalogs, by marking the position listed for that row. The results of subsequent searches will be stored in new tables, accessed by clicking on the tabs at the top of the Results panel. To eliminate a results table (and discard the results for that search), click the "x" icon on the tab. Concurrent searches are possible; if a new search is initiated prior to the last one completing, a new tab will be created while the previous search continues. Just below the tabs is a status panel with the following items from left to right:

  • the number of rows retrieved (and update information for searches in progress)
  • controls for AstroView (more on these later)
  • an Export Table As... button which can write the table of results to your local storage.
  • the object name and coordinates from the name resolver
  • the search radius
Fig. 3—Appearance of the DDT after a search for m57 within radius = .2 degrees, showing the filters (left panel) that can be applied to the Search Results (center panel), and the AstroView component. The results of a prior search/tab may be viewed by clicking the tab (labelled Start Page in this case) at the top of the Search Results panel.

The records are listed in the table, one per row. Each record represents data about a particular image, catalog or spectra, with the columns defining each datum about the record. In the example above, each displayed record is about an IUE spectrum that was found within the bounds of the search.

Search Details Pop-Up

Clicking on any row in the Search Results panel pops up a panel with summary information about the resource; clicking the double arrows at the bottom of this panel (labelled "Expand for Details") exposes all of the attributes for the resource.

Fig. 4—Summary of a m57 resource, showing the summary description of the resource. Clicking the double-arrow (circled) at the lower-right of the pop-up brings up all available details. Different details panel formats exist based on what is being viewed - resource information, an image, a catalog or spectra. Sometimes the tool can only provide a generic view of the record.

Refining Results with Filters

Many searches, particularly on popular targets or of a sufficiently large area of sky, generate sometimes hundreds or even thousands of rows. The Filters panel allows the user to restrict the list of search results to those of most interest.

Facet Filters

The list of potential filters is quite large, and includes as many attributes of the matched data collections as the data providers offer. The filters in the panel are grouped into semantically related facets depending on the data. You can view the list of allowed facets by clicking the Edit Facets button at the top of the panel; select the desired facets by clicking the check-boxes in the pop-up window (middle) and clicking the Apply button. Note that not all facets are displayed or even available by default.

There are three types of filters:

  • Discrete filters - Used for text and most integer-based facets (columns of data). A filter can be applied by clicking the check-box next to the desired facet values.
    • A special discrete filter can exist when the data rows are selectable, allowing the user to choose whether to filter selected or unselected rows.
  • Ranged sliders - Used for continuous numeric data, some integer data, and dates. Each facet presents the user with a histogram approximating the distribution of the data, a 2 handled slider for constraining endpoints, and a min/max box displaying the current endpoints, which also allows a user to manually type the desired endpoints. Some numeric facets are known to have certain values that represent a null or undefined entry, and the facet will alert the user that it is ignoring such a value.
  • A search box, which allows regular expression matching by searching all records and columns of the data (even ones not visible in the display grid).
filtered search
Fig. 5— The search has been filtered by constraining the RA bounds. For example, only 76 of the rows where "ex" is 0 remain in the grid. Regular expressions may also be used as filters by entering a regular expression (usually just a word) in the dialog box near the top of the panel. In the numeric facet above, the data was recognized as RA coordinates and is presented in these boxes in sexagesimal format, but a user may define his or her own bounds using sexagesimal or degrees. Pressing the "Zoom to Range" button spreads the histogram out to cover only the originally selected range.

Retrieving Results

A core capability of the DDT is to enable users to download resources, or to direct them to other desktop applications for analysis. As used here, resources is a rather generic term used to refer to individual data files (images, tables, and the like), or collections of them, or to services that provide data upon request. Any of these resources may be of use scientifically, and the DDT has simple mechanisms for retrieving them.


Downloading catalogs or tables is somewhat simpler than downloading images, in that any table displayed in the results panel may be saved with the following steps:

    1. click the Export Table As... button
    2. select the output format and other parameters from the pop-up panel
    3. click the Export button

Broadcasting Data via SAMP

Many popular applications, including TOPCAT, Aladin, and DS9, have the ability to receive data from another similarly enabled desktop application . The DDT can broadcast a table, via the Simple Application Messaging Protocol (SAMP). The procedure is the same as downloading a table, except that instead of clicking Export as the last step, click the Broadcast button. Note that at least one other SAMP-enabled application, such as TOPCAT or Aladin must already be running in order for data to be transferred anywhere. When a table is broadcast (in this case, from the DDT to TOPCAT) for the first time during a session a security notification may appear.

Finally, note that the DDT does not currently support receiving broadcasts of data from other applications.

The AstroView Tool

The AstroView Tool is an all-sky-viewing component developed in Flash. It uses the same positional search and name- resolving capabilities as the DDT, but instead of displaying tabular results and image files it presents a view of the sky from Earth. This view can be panned, zoomed and searched, and the imagery displayed can be changed based on the survey selected using the tool.

One interaction between the DDT and AstroView is the notion of projecting image "footprints", i.e. the detector shape, size and orientation for a given image, onto the survey images. Selected rows in the grid are highlighted in this tool. Clicking footprints or markers in AstroView will not only highlight them, but will select them in the grid and bubble them to the top. Selecting is somewhat inexact by design - many footprints overlay each other exactly, so many rows may be highlighted in the grid with a single click. Figure 6 demonstrates footprints and highlighting.

The AstroView controls listed for each grid contain 3 components (circled in Fig. 6 below):

  • Display - A toggle indicating which footprints are to be displayed
    • None - show no footprints
    • All - show all footprints. Unselected footprints will be the color of the swatch, and selected footprints will appear slightly highlighted.
    • Selected - show only footprints that are selected in the grid. This acts as a filter for the tool, and can help viewing a crowded area.
  • Color - a swatch indicating the color of footprints associated with this search. Each search result is automatically assigned a new color to help distinguish its graphics from those of the previous searches.  Clicking on the palette icon allows the user to select a new color for this search.
  • Palette button - allows user to pick the color for this grid's footprints.

Fig. 6—Footprints are from images selected in the table view, then the AstroView controls, then brought to the top in the AstroView display grid..

Tips & Notes

When formulating a search, note the following:

  • Leading zeros are ignored in the name. For example, M5 returns results for object Messier 005.
  • Object names are not case-sensitive, and spaces between the characters (e.g. M51 and M 51) are ignored unless the space indicates a real character in the name.
  • If an object name is incomplete the name resolvers from NED and SIMBAD return the closest match. This can lead to surprising results however.
  • All coordinates are interpreted as J2000.
  • Maximum search radius is limited on a collection-by-collection basis.
  • Queries are currently limited to a single object or position. However, multiple queries may be submitted sequentially, even if one or more queries are still executing.

When downloading an image, note the following:

  • Large images may take a while to download. Progress can be monitored using browser tools.
  • Downloading is disabled for data products that are embargoed by the provider. It may not be obvious when this happens, except that no file will be downloaded to your computer.

When downloading a table, note the following:

  • The Export Table As... operation refers to the currently visible table, and not to a selected row within the table.

When broadcasting a table, note the following:

  • At least one other SAMP-enabled application, such as TOPCAT or Aladin must already be running in order for data to be sent anywhere.
  • The DDT cannot currently receive data sent from other applications.

Tabs of search results are not saved between sessions; once the application has been abandoned, returning to it will not bring up previously searched objects.

User feedback on this tool is welcome and encouraged! Contact the VAO.

Last modified: June 6, 2012

© 2012 VAO, LLC