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TEQC Hatanaka 		Data - Frequently Asked Questions about GSAC

Question 1:

What is a Seamless Archive?

Answer:

The GPS Seamless Archive Centers is: (1) a simple method for finding and using GPS data stored at participating data centers; and (2) the implementation of a specific strategy to identify and retrieve GPS data sets. The "seamless" part means that a user accessing a single data center can see what data exist at any of the other participating centers, without the user necessarily having to a priori know the actual location of either the other center or know about the centers data holdings.

Thus the participating data centers are seamlessly linked from the user's perspective. (Of course the data centers have to do some work to organize their data into a standard and agreed upon manner, so to them there is some work involved.)

Question 2:

I need to find GPS data. How do I use GSAC to do that?

Answer:

There are two retailers (SOPAC, UNAVCO) for Web based searches. You can also use a command line client available from SOPAC. A PPT tutorial for using the retailer and command line direct is available. You can obtain software to assist in your wholesaling from SOPAC.

Question 3:

If there is work is involved, why would I wish to participate as a wholesaler in the GPS Seamless Archive Centers (GSAC)?

Answer:

Some responses for differing situations include:

  • You might already be distributing GPS data, and over time may find that some effort is already spent on requests for data or on the details of long term management. GSAC can help by standardizing, and by sharing in solutions that others have already thought about.
  • You may be looking for a simple indexing scheme useful to track your legacy and newly arriving data.
  • The GSAC is a participatory process with the belief that many different groups are already doing the same sorts of activities and that with some minimal collaboration and tool sharing the work load will be reduced for everyone.
  • Improve data preservation.
  • Notify others where data exist, as a general service.
  • Simplify distributing data, for collaborative work.
  • Meet institutional or funding manager's goals for data publishing.

Question 4:

What specifically does it take to become a GSAC wholesaler?

Answer:

You must publish information about your data holdings as defined in a data exchange document which specifies two tasks:
(1) Create an FTP- accessible directory tree
(2) Populate certain files stored in specific locations under that tree with information describing your GPS data holdings. Although the details of how to set up these GSAC "data holdings" files may appear complex, in fact these files simply include summary information which can be gleaned from accurate IGS-style log files and from information gleanable from accurate RINEX file names and RINEX header information.

Question 5:

Who is already doing GSAC file listings?

Answer:

A list of active participants is kept as up to date as we can. Please contact us once you have started keeping your GSAC files on line so you can be added to the list.

Question 6:

If I want to participate as a GSAC wholesaler can I limit the data distribution?

Answer:

The GSAC files describe what data you have; where survey markers are located (to a precision which you specify); when GPS data starts and ends for those surveys. But the data are distributed only if you make them available, for example via anonymous FTP. Some centers prefer to be contacted prior to data release. In this case the GSAC description file will contain for example, a URL pointer to the contact information, rather than a pointer to retrieve the actual data.

Question 7:

Who manages the GSAC activities and how do I contact them?

Answer:

The idea for a seamless archive originated in UNAVCO community meetings, but the GSAC is meant to be as broad as the user community is willing to expand it. At least for the short run, the US National Science Foundation is providing funding for the development of archiving and access tools, maintenance of the web pages, and coordination of participants. Activities are currently managed by a working group that includes representives of the participating archives and the UNAVCO Community Coordinator.

Question 8:

What is the status of GSAC activities

Answer:

Six "wholesaler" archives have indexed all of their data holdings according to GSAC specificiations, and two retailers, SOPAC and UNAVCO, are providing access to GSAC holdings.

Comments or questions about this page? Send e-mail to Lou Estey (louunavco.org).

Last modified Monday, 26-Nov-2007 14:34:40 MST
 

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