2010-08-27: Virtual Workshop WCS Implementation

Main ESIP page >> Main AQ Work Group page >> Interoperability of Air Quality Data Systems | Standards Implementation Virtual Workshops

Telecon/Screenshare Info

1:30pm EDT
Phone: 866-489-0573 (US, Canada, VOIP); 205-354-0149 (international)
Meeting Code: *2279431*

Screenshare details:
Please join my meeting, https://www1.gotomeeting.com/join/954083041

Introduction

Who is this workshop for? Anyone interested in:

• Making their data more widely accessible
• Using standard tools and catalogs instead of custom-made
• Need help adding a standard interface to data

Participants in this workshop may have varied backgrounds on web services (from novice to expert). The varied experience will allow participants to form mentor relationships.

Problem: Data is distributed, in different formats and can't be accessed by common tools within the AQ Community

Solution: Create a standard interface to the data using OGC Web Coverage Service

• Introductory Screencast to WCS (5 min): Data Access through OGC WCS Protocol

In-depth Details (programmers?)

Case studies of how Data Systems Implemented WCS:

• DataFed - Kari Hoijarvi, Rudy Husar
• DLR
• Giovanni/NASA - Wenli Yang/Greg Leptoukh
• RSIG - Todd Plessel
• Airnow- Steve Ludewig/Tim Dye
• Univ. of New Mexico - Karl Benedict
• Unidata - Ben Domenico

How-To

Questions about WCS

What WCS questions/issues have you encountered? If you know the answer to these questions please respond below the question with ** and add your name.

Questions from Steve Ludewig, Sonoma Tech

• The WCS protocol – how can/should it be extended for air quality
  • Units are the most glaring omission.

<units>ug/m3</units> RSIG includes units in the label: <label>pm25_daily_average(ug/m3)</label> -- Todd Plessel

• How should we handle different or even multiple parameter requests? (separate arguments? Lists as arguments?)
  • At the WCS URL level, V1.0.0 only allows one variable per request while V1.1.x allows multiple variables. If a client or portal is provided (e.g., the DataFed browser), the client or portal should be able to handle multiple variables case even in V1.0.0 by sending multiple requests. -- Wenli Yang
  • Comma-separated list. E.g.,COVERAGE=aod,std,cld,cls,sfc,ch1,sig,mos RSIG example: http://badger.epa.gov/rsig/rsigserver?SERVICE=wcs&VERSION=1.0.0&REQUEST=GetCoverage&COVERAGE=gasp.aod,gasp.std,gasp.cld,gasp.cls,gasp.sfc,gasp.ch1,gasp.sig,gasp.mos&AOD_RANGE=0,1&STD_RANGE=0,1&CLD_RANGE=1,1&CLS_RANGE=5,25&SFC_RANGE=0,0.5&CH1_RANGE=0,0.3&SIG_RANGE=0.01,0.5&MOS_RANGE=0,0.5&TIME=2008-06-21T22:00:00Z/2008-06-22T12:00:00Z&BBOX=-76.1,38,-75.5,39.6&FORMAT=ascii -- Todd Plessel
• Duration codes?
  • WCS spec is a UTC time range, e.g.,: TIME=2006-07-05T00:00:00Z/2006-07-09T23:59:59Z so all WCS implementation should support this.
• Parameter occurrence codes (POC)?
  • More trouble than they're worth for most users who would rather just think about named variables over time and spatial ranges. (But feel free to extend your own implementation if needed to support your users.) -- Todd Plessel
• Time_Sequence: Ours currently is a single date/time -- should it accommodate a time range (performance is a concern)? What time standard? (UTC?)
  • The GSFC WCS servers support time range and will pack multiple time slices (e.g., daily, monthly) data into one single file, thus increasing the dimensionality of the output, e.g., 2D spatial => 3D spatial and temporal. There might be, however, a performance issue. If a client requests a long time period, e.g., an entire year, for a daily product, the server may not be able to fulfill the request. Chris Lynnes suggested that the server only do one time step, which means that the client shall send multiple requests for multiple times and assemble the after receiving the data. --Wenli Yang
  • Yes. It must to be WCS-compliant. Absolutely otherwise it cannot be readily combined with other global data. WCS spec is a UTC time range, e.g.,: TIME=2006-07-05T00:00:00Z/2006-07-09T23:59:59Z

so all WCS implementation should support this. -- Todd Plessel

• Use of an API key for authentication.
  • Authentication should not be required for a pubic WCS. (But customize yours if you must.) -- Todd Plessel
• Output (payload) formats
  • This is a crucial aspect for compatibility and performance that is not addressed by the WCS spec (presumably since it is not a data model). E.g., FORMAT=netcdf does not specify the conventions.RSIG supports the following output formats: http://badger.epa.gov/rsig/webscripts.html#output
  • GSFC servers currently support HDF-EOS and netCDF-CF1, but there are issues for some coverages in CF1 compatibility. --Wenli Yang
• Field naming
  • CF Conventions may eventually become widespread, but they need to be extended for AQ variables (e.g., see CMAQ variable names). -- Todd Plessel

Implementation of WCS

• WCS Access to netCDF Files
  • Videos with Kari Hoijarvi (DataFed Programmer): Overview of WCS Framework | Explanation of Configuration File | Explanation about the project, details on actual installation
• Minnesota Maps WCS

Testing Services

• WCS Service Tester - Tests DescribeCoverage and GetCapabilities
• OGC Test Engine
  • WCS Test Executive Summary | WCS Assertions and Test Requirements
• Previous Service Interop Tests

Outcome

List your server here if you have a WCS implementation. Test with the Service Checker for GetCapabilites, DescribeCoverage and GetCoverage with the WCS Service Tester

• DataFed - Passed GetCap/DescribeCoverage
  • Base URL http://webapps.datafed.net/AERONETd.ogc
  • Tested Coverage: COVERAGE=AOT_1020
• RSIG -Passed GetCap/DescribeCoverage
  • Base URL http://badger.epa.gov/rsig/rsigserver
  • Tested Coverage: COVERAGE=airnow.pm25
• DLR - Passed GetCapabilities/DescribeCoverage
  • Base URL http://wdc.dlr.de/cgi-bin/gome2_o3_w.cgi
  • Tested Coverage: coverage=GOME2_O3
• CIESIN - Passed GetCap/DescribeCoverage
  • Base URL http://beta.sedac.ciesin.columbia.edu/mapserver/wcs/coverage/GPWv3
  • Tested Coverage: gpw_popdens_2010
• Unidata - Passed GetCap/DescribeCoverage
  • Base URL http://motherlode.ucar.edu:8080/thredds/wcs/fmrc/NCEP/GFS/Global_0p5deg/runs/NCEP-GFS-Global_0p5deg_RUN_2010-08-24T12:00:00Z
  • Tested Coverage: ICAO_Standard_Atmosphere_Reference_Height_tropopause
• Other Available services

Participants

Next to your name add if you are looking for guidance or have implemented a successful WCS and could provide guidance

Next Workshop

We will continue the discussion on WCS in telecon/webex form in 6 weeks. In hopes that the information gained from this session can be implemented/tested and we can move forward with a set of interoperable web services.