Using OGC Web services for discovering EO data

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Using OGC Web services for discovering EO data
Presented by Thomas Lankester 16th February 2006
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Scope

• To define Web Service interfaces that will allow
  Earth Observation (EO) data to be discovered from
  scattered repositories in a seamlessly fashion.
• Geographic Web Service specifications are defined
  by the Open Geospatial Consortium (OGC).
• True interoperability with OGC interfaces
  requires a user community to take responsibility
  for defining conventions for use.
• These conventions for use are called
  specification profiles.

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ESA Initiative

• ESA has proposed
• OGC Catalogue Services
• Minimal Profile for EO products
• The final goal being to agree to a coherent set
  of interfaces for catalogue and order of EO
  products to support access to data from
  heterogeneous systems dealing with derived data
  products from satellite based measurements of the
  earths surface and environment.

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So long, and thanks for all the fish
Saw-id!
Job done, cheerio, toodle pip, etc.
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BUT ..inspired from the catalogue abstract
model..
Application Client
OGC catalogue interface
OGC service interfaces
Ö
X
Catalogue Service
Distributed search
Metadata Repository
describes
Resource
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BUT ..inspired from the catalogue abstract
model..

• ESA catalogue profile (level 2)
• needs to be harmonised with the OGC Cat-2
  specification
• extends Cat-2 with product order capabilities.
• OGC procedure
• to be released for 30-day public consultation
• electronic vote
• release as Version 0 and a Revision Working Group
  (RWG) is set up to address the comments.

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Action 1 support ESA initiative by responding
to consultation

• Paper study review of ESA profile
• Tire kicking exercise build profile compliant
  Web service interface (search but not order)
• Provide feedback during the 30-day public
  consultation period.
• Known issues, the profile needs to
• distinguish between the responses to search and
  present requests
• provide more examples (e.g. for order requests)
• better explain / tightly define individual
  elements and attributes (e.g. idAbs).

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ESA catalogue search and order interface
operations
Input Payload Message searchRequest (collection
level) presentRequest (inventory
level) productOrderRequest (archive/process/acquir
e) orderMonitorRequest
Output Payload Message response (collection
metadata) response (product metadata) productOrde
rResponse orderMonitorResponse
includes URL of browse image
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Action 2 define a new profile for interactive
browse

• Why?
• Not a map, just an image
• No display resolution control
• No band selection (just default greyscale or
  false colour)
• No bitmask checking

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Action 2 define a new profile for interactive
browse

• How?
• Web Coverage Service (WCS) interface
• access grid of real data (coverages)
• range of scale, choice of Coordinate Reference
  Systems (CRS map projections)
• cookie cut area of interest.
• Web Map Server (WMS) interface
• serves monolithic map layers (JPEG, etc.)
• range of scale, choice of Coordinate Reference
  Systems (CRS map projections).

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Action 2 define a new profile for interactive
browse

• Which?
• Web Coverage Service (WCS) interface
• immature, WCS v1.0 being revised
• high bandwidth requirements for data delivery
• overkill for discovery
• flexible.
• Web Map Server (WMS) interface
• mature, WMS 1.3 is also an ISO standard
• supports typical compressed WWW image formats
  (lower bandwidth requirements)
• less flexible but possible for discovery.

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Action 2 define a new profile for interactive
browse
WMS profile for interactive EO browse (level 1)

• the basic unit of geographic information that may
  be requested as a map from a WMS server is a
  layer
• convention for EO community layer dataset
  type
• the TIME parameter is mandatory and used to
  select specific products.
• http//eoltd.co.uk/mapserver.cgi?VERSION1.3.0
  REQUESTGetMapCRSCRS84 BBOX78.105,24.913,9
  4.794,36.358 WIDTH560HEIGHT350
  LAYERSMER_RR__2PSTYLESFORMATimage/png
  TIME2002-07-01/2002-07-31

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Action 2 define a new profile for interactive
browse
WMS profile for interactive EO browse (cont.)

• default browse maps e.g. greyscale (SAR), false
  colour (optical), pseudo-colour (geophysical)

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Action 2 define a new profile for interactive
browse
WMS profile for interactive EO browse (cont.)

• use of sample dimensions to specify individual
  wavebands (only 1 or 3 may be specified)
• DIM_MDS15,8,4 returns RGB false-colour image
• DIM_MDS17 returns greyscale or
  pseudo- colour image
• use of nested layers to contain bitmasks with 10
  standard colour styles.
• LAYERSABSOA_DUST,MEDIUM_GLINT,ICE_HAZE
• STYLESYELLOW,PINK,BLUE

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Timescale

• Action 1 - respond to public consultation on ESA
  catalogue profile March 2006
• Action 2 define new profile for interactive EO
  browse
• define GetMap request/response, March 2006
• develop, present and submit profile 2006/07?