An Interface to

On-line Archive
 Science Information Services

Oasis provides access to data from many sources, including
Client GIS functionality allows fusion multiple datasets simultaneously. A general mechanism allows easy extension with other third-party data.

OASIS Quick-Start User Guide

Data Retrieval Data Processing Control/Info Data Interaction

Oasis is a pure Java interface to several of the large-scale astronomical image and catalog archives around the world. It provides a uniform interface for locating data based on sky location or object name (using the NED and SIMBAD name resolution services) and, in the case of catalogs, on relational (database table) field constraints.

Retrieved data can be layered together using a GIS-style sky visualizer and a table viewer. The relationships between datasets can then be examined interactively through image-to-table feedback and other mechanisms.

The system provides a very powerful mechanism which allows data and service providers to utilize Oasis functionality for display of their own data (alone or inconjunction with data from other sources) without the need for any software installation or requiring that data pass through any third party.

These "Oasis Links" are simply reformed URLs to the data or service constructed in such a way that a single instance of Oasis can be be asked to retrieve the data directly from the specivied URL location. More information is available in the On-line HelpRe.


Data Retrieval

Oasis Main Window
When Oasis first comes up, the user sees a blank map display window and a set of controls for accessing the Oasis archive search and data manipulation functionality. Any FITS image file can be opened from the local disk or an image can be retrieved from any one of several servers. Similarly, corresponding catalog data can be retrieved from IRSA or CDS. All these functions (and most of the rest described below) are accessible through icon buttons on the main window.
Image Archive Search Window
Image archive access is handled through an integrated combination of general and specific search criteria. This form allows the user to enter an object name or location and specify where to save the resulting FITS file. Tabbed subpanels provide the mechanism for selecting which image set to search and allow for archive-specific search criteria.
Catalog Archive Search Windows
The second, third and fourth buttons on the main window provide a means for users to search catalog archives at IRSA and CDS (VIZIER) and perform a region search using NED. All three return a source table (which will then be automatically overlayed as a map on any image displayed). IRSA and CDS also allow relational search constraints in addition to sky region constraints (in the case of IRSA, the sky constraints are optional and full SQL can be used if necessary to allow AND and OR constructs).
Third-Party Services
Oasis provides an open-ended mechanism that any data owner or service provider can utilize to make their information available using the Oasis toolkit. Since we cannot know all the ways in which Oasis is being used, the list provided here simply represents a snapshot of those services we currently know about.


Local Data Processing

Contour Generation
Oasis includes a general "sky drawing" capability based on an XML dialect (not yet finalized). On top of this, we have built a tool which takes an image as displayed and, using the data range chosen by the user as a starting point, generates a contour file. Since this file is drawn in sky coordinates, it can persist as an overlay even if the underlying image is changed.
Image Subsetting / Resampling
In order to deal with very large images, we provide a mechanism for interactively cropping out a region of interest and/or subsampling the data (i.e. reading every nth pixel/line. This has the same effect visually as zooming/panning the full image.
Coordinate History
Oasis provides a straightforward mechanism for maintaining a coordinate history. The user can save the "current location" (the last point selected on the image or in a table) to a memory list, use this last-saved location in a variety of places (archive search GUIs, on third-party Web forms), or view/edit the complete history and save it to disk.


Control / Information Windows

Color Control
All the standard functionality is available for controlling the details of the display. Data stretching can be based on absolute values or percentiles of the data itself, and the user can switch easily between the two. Color stretching can be either to specific values or done interactively.
Zoom/pan functionality is provided through a pop-up which presents a small version of the whole image plus an outline of the portion currently displayed in the main window. Fractional zoom factors (e.g. 1.75) are allowed.
Layer Control
Data overlaid on the images (source maps, coordinate grids, contour plots, etc.) are handled as a set of map layers and controlled through the Layer Control window. From here, for instance, the user can modify symbol sizes, etc. for map overlays. They can also ask that the tables that were used to make the map be shown. Sources selected in the table can be highlighted on the image (and vice versa).
FITS Header Display
Oasis will display a summary of the information in any FITS file (including extensions). This tool will be eventually be used to allow access to extension data and planes in data cubes, though this capability is not yet available.
Request Management
All data requests (whether from the Oasis custom archive search functionality, data references in tables, or from third-party services) are handed off to a centralized request manager. Since our current services are simple URL data requests, this is instantiated in a File Transfer Manager front-end through which the user can monitor all outstanding data requests and control (cancel or redirect) their progress.

There is an active project at IRSA to implement a more involved Request Management service (for handling lengthy processing jobs among other things) and another to build an integrated Data Collection interaction environment. When these and Oasis are integrated together, the functionality here will be greatly expanded.

Show Image History
Users frequently wish to quickly switch back and forth between two or more different images. Oasis provides an "image history" window which lists the various image files which have been viewed and remembers the details of the display in each case.

For example, if the user first displays a DSS image of M31 adjusting the color table, stretch, zoom, etc. then displays a 2MASS image of the same region with a different color table, stretch, zoom, etc., the image history will remember and reset all the display details as the user switches back and forth. This works for any number of images.

Show Selected Source Info
Oasis maintains and can display many source tables as overlays to the current image. When a user selects a location on the sky or region, all of the sources in that region are marked in their respective tables. With many tables, however, the screen rapidly becomes too cluttered for this to be effective so Oasis does not display tables unless asked.

Instead, a special "source info" window pops up. In this window the user can see all of the information for a single table record (arranged vertically as field=value pairs rather than horizontally) and can step forward and backward through this list.


Data Layer Interaction

Catalog Table Display
The table retrieved through the catalog search form and controlled using the Layer Lontrol window is shown at left. The details of how it is rendered can be set through Layer Control.

When the user selects a location on the display or an area of interest, the system interrogates all active layers. In this case the area of interest is being set through an area examination window. Information about the image for this region is shown, but since the table map layer is also active, all the sources covered by the circle are also marked (both on the image and in the table).

Map Symbol Control
From the Layer Control window, once a table layer has been selected, the way in which the map is constructed (symbol color, shape, size, etc. can be specified through this window (brought up through the "Edit" button on Layer Control).
Layer Feedback
When the feedback mode is set to area, or when a position is specified (via the Feedback pulldown or the area examination button) and an area defined, all layers that are selectable (e.g., the background image and all active tables) are queried for information. For the image, the result is area flux statistics (shown at left). For the tables, all appropriate sources are marked in the table (the highlighted records in the table above) and on the map (the black and white boxes overlaying the source symbols on the main window).
Rescale Overlay Grid
For effiency, the coordinate grid is only computed for the region of the image which is currently displayed. As the user zooms or pans, this tool (under the Display menu) allows them to recompute this overlay on demand.


Active Table Feedback

NED Basic Data Table For basic catalog searches, the table cells are simple data measurements. For other tables, certain cells can represent links to additional data. In the case of the NED basic source data (shown at left) some of the columns are encoded in such a way as to indicate that they are external links, in this case to either the NED detailed source data or to the ADS abstract server.

Activating either of these links causes a browser to come up and to which is passed the URL in question. The results for a specific object are retrieved and displayed.

NED Detailed Data (Browser) The NED detailed data for the source highlighted in the above table is shown at left.

Data References Other table references are to additional data files (images, source catalogs, spectra, etc.). In these cases (based on the MIME type of the returned information), the data is either added to the existing display (if an image or source table) or sent to some other renderer, as in the case of the AAVSO lightcurve shown.


Additional Functionality

Oasis provides a wide range of functions not described here, including:

  • Telescope focal plane overlays (SIRTF only at this time)
  • Context-sensitive help
  • An interactive drawing layer (limited at this time)
  • Local printer (or PostScript file) output
  • JPEG image file output
  • Coordinate feedback (with full precession capability)
  • Multiple coordinate grids (any system and epoch)