From Ocean Teacher Library
Live Access Server (LAS)Contents |
Background
- "The Live Access Server (LAS) is a highly configurable web server designed to provide flexible access to geo-referenced scientific data. It can present distributed data sets as a unified virtual data base through the use of OPeNDAP networking. Ferret is the default visualization application used by LAS, though other applications (Matlab, IDL, GrADS, ...) can also be used." [From the LAS homepage, see below]. The most current version is LAS 7.0.
- When properly configured, a LAS server can provide complete or subsetted data and images, both from its own data cache and from other OPeNDAP-compliant online sources. A wide variety of output formats have been experimented with over the history of LAS, of which only the NetCDF output is really useful. Image output is interesting, but often not landmasked. Some ASCII output formats are nicely formatted for visual inspection, but not compatible with any known software. The so-called Arc Grid output often has unequal row and column dimensions, violating the actual ESRI specification, in which case the files are useless for GIS.
- Numerous LAS servers are included in the Data Websites and Catalogs section. A complete list of LAS servers is provided by the LAS home page link below.
Example LAS Data Request
- Here's a sample request in XML format [quoted from the product request paper below]:
<lasRequest href="file:las.xml">
<link match="/lasdata/operations/shade" />
<args>
<link match="/lasdata/datasets/COADS_1degree_Enhanced/variables/air947"></link>
<region>
<range type="x" low="-180.0" high="180.0"/>
<range type="y" low="-89.5" high="89.5"/>
<point type="t" v="01-Jan-1960"/>
</region>
</args>
</lasRequest>
- And here is what it looks like when all special characters (e.g. ", =, <, >, /) have been replaced by ASCII escape sequences. [The specific arguments are slightly different; this request is for the GHRSST dataset, view (xy), full region for Aug-14-2009 00:00:00:] This example digital sequence, which would be transmitted over the web, was provided by the US GODAE LAS staff:
The OPeNDAP protocol is so straightforward, that the user can simply use SAVE AS with the above URL to capture the required NetCDF file locally. [Caution! 30 MB] With care, the URL can be directly edited to provide other data, dates, or geographic subsets. But this would be much easier in the LAS itself.
Other Resources
- LAS Product Request API - Examination of this short paper reveals how the XML-based request syntax is formatted by the LAS
- Live Access Server - Homepage for downloads and documentation; includes a list of known LAS servers worldwide
- National Virtual Ocean Data System - Probably the best-known and largest LAS implementation; contains a huge amount of climatological data
Subsections of this Article
No subsections available
Information about this article
Short title: Live Access Server
Description: none
Expertise level: beginner
Author: Murray.Brown
Approval status: approved
Approved by: Murray.Brown
Last change: 2009-8-17
Subsection of: Open-Source Project for a Network Data Access Protocol (OPeNDAP)
Contact
If you have any direct comments or suggestions for the author of this page then please feel free to send an email to the author (listed above). For discussions on this page please use the discussions page.
