VO Desktop is a launching point for doing science using VO tools. It uses a resource centred approach. First you choose the resources you are interested in by searching the registry of resources. Next, you query the chosen resources to look for and fetch the specific data you want. Finally, you either save the data (to VOSpace or to local disk) or pass the data on to another application (eg an image viewer like Aladin), to start doing some science analysis.
The Registry of Resources
The Registry stores information about Resources all round the world. A "Resource" could mean a data collection like UKIDSS, or an application like Sextractor that you can invoke as a remote service, or just information about an organisation. Data collection resources will usually have one or more "capabilities", i.e. ways of accessing the data, like an image cut out service, or a catalogue conesearch, or a full query-language (ADQL) interface. Each registry entry contains metadata describing the resource - basically a set of standard attribute=value pairs. This information will tell you whether the resource is a catalog or an image atlas, whether it has infrared or X-ray data, who curates the data, and so on, but won't tell you whether your favourite source is included. For that you need to send a query to the resource itself. Note that the Registry is maintained by AstroGrid, but the information in it is provided by the resource owners, not by the AstroGrid project.
Choosing and bookmarking resources
The total number of entries in the AstroGrid registry is very large, so you need to start by filtering down to those you might want. The VOExplorer tool gives you several ways of doing this. (i) It provides some pre-defined lists that you can start working on. (ii) Using a set of "filters" rather like you would see in an mp3 player interface, you can trim down the list further. (iii) You can create a completely new list by using a search form where you specify for example that you want only images, only in the infrared, and only collections that have UCDs such and such. (iv) You can save that list, and as well as loading it back another day, you can add and subtract specific resources.
There are two types of list - Static Lists, and Smart Lists. The latter saves the rule you used to create the list, rather than the list itself. This means that when the Registry gets updated, if you run it again in six months, you might get a different list.
Note that your saved lists will still be available when you update to a newer version of the software.
Viewing information about the chosen resources
The Resource List pane gives brief information about each resource in the current list in a single line. If you select a specific resource, more detailed information is provided in the Resource Information pane. This pane has several tabs showing information in different ways - for example a formatted html view of key items, the table column metadata where appropriate, and, specially for the geeks, the raw XML. There is also a link to the publishers own web page, where much more information can be found.
Querying/invoking the chosen resources
You can now choose one or several resources to invoke or send queries to. The Action pane will contain one or more possible actions depending on what sort of resources you have selected, and/or their "capabilities". There are three main possibilities.
The first are positional search capabilities. For single object searches the Astroscope tool is launched when clicking on Query. If you have selected catalogues that advertise a conesearch capability, you can launch Astroscope and type in a single RA, Dec or Simbad object name and search radius. From v220.127.116.11 (May 2009), the user may now upload a list of such positions if desired using a separate Multi Query task option. Each selected service then produces a VOTable with a list of sources satisfying your parameters (including the possibility of an empty table !) for each input position. You can then pick one or more of these to save, or to load into Topcat etc. Likewise, if you are looking for images or spectra close to some position on the sky, you would find them with Astroscope, but the returns would be FITS files, or GIFs etc. It is also possible to search on all possible VO resources for single or multiple positions and radius by e.g. launching All-VO Astroscope from the Windows drop-down menu in VOExplorer but the number of returns may be very large! When querying solar resources, a slightly modified version of Astroscope appears, known as Helioscope.
The second possibility is the Query Builder. This is the interface you use if the chosen resource is a database that advertises a full query language (ADQL) capability. ADQL is a VO-standardised version of SQL. Query Builder picks up the metadata from the service about what tables it has and their column names, so you can construct a query along the lines of "give me entries with RA between this and this that have BMAG<23 and data quality flag = 3". You also set which columns you want returned. Like with conesearch, the return will be a VOTable. If you know what you are doing, you can also type the ADQL straight into a text window.
The third main possibility is the Task Runner. This is what you use if you have selected a resource which is a so-called "Remote Application". These are just scientific applications like Sextractor, or Hyperz, but which have been set up on a server somewhere to run at your request. You give it the required input and output parameters, press go, and it chugs away on the remote server until its done. As well as specifying parameters, you usually need to specify the location of both input data (e.g. an image to run Sextractor on), and output data (e.g. the extracted source catalogue expressed as a VOTable).
Carrying on from there
Once you have found the data you want, you can save the relevant files, either to your own local disk or to your VOSpace account. It is then available for use later with your favourite data analysis tools. However, if while you are using VO Desktop you already have tools running which are "SAMP compatible", you can pass data straight to them. SAMP is just a standard protocol which allows applications to pass messages between each other. VO Desktop knows what other SAMP apps are running, so if there is a suitable choice, it will appear as a choice in the Action pane, as something like "Send to Aladin".
Looking at your files
With the File Explorer tool, you can examine both your local filespace, and your VO Workspace provided by AstroGrid. Note that to use the VO Workspace you need to have registed an account with a community. File Explorer also recognises standard file types such as VOTable and FITS, as well as JPEG, EPS etc, so can give you appropriate options for viewing or analysing a file.
Follow these links to for a description of how to use the tools that are launched from VODesktop: