Online Data Access using WCS and GMLJP2 Alexandre Robin Spot Image Didier Giacobbo Spot Image Steven

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Online Data Access using WCS and
GMLJP2Alexandre Robin Spot ImageDidier
Giacobbo Spot ImageSteven Smolders GIM
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WCS quick overview

• WCS stands for Web Coverage Service.
• The purpose of this OGC standard service is to
  provide a client with portions of coverage
  according to client request parameters.
• WCS is a mechanism for distributing through
  Network Services spatiotemporal portions of
  coverage.
• A coverage may be seen as contiguous digital
  spatial multi-temporal and multidimensional
  information
• Remote sensing raster products are coverages
• Serve coverage information filtered by client
  parameters through 3 types of requests
• GetCapabilities describes available coverages on
  the server and the abilities of the server to
  serve these coverages
• DescribeCoverage describes a single or a set of
  coverages
• GetCoverage provides the portion of the coverage
  required by the client according to the client
  specified parameters

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WCS for Earth Observation

• Main EO data characteristics
• EO Sensors may acquire data with multiple
  wavelengths
• provides a stack of many layers of data
• strong correlations exist between the different
  wavelength bands
• Due to the EO sensors revisit capacity EO data
  allows to provide information on the same
  phenomenon at various time instances
• EO data is provided with positioning ancillary
  data that allows the georeferencing of the images.

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WCS for Earth Observation

• EO data may be used in raw rectified or compound
  forms.
• The raw observation reflects the acquisition
  process
• The rectified or compound coverage represents the
  data ready to be used by any Geo Tool (GIS Image
  Processing Software Web Portal)

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Why WCS for EO data

• WCS is by concept spatially enabled
• WCS handles temporal data
• WCS allows retrieval of stackable data by
  resampling the coverage to fit the client
  request.
• WCS handles range values domains
• WCS has the ability to deliver metadata about the
  EO product acquisition its production process
  and its usability
• WCS as opposed to WMS provide pixel values as
  close as possible to acquired data

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WCS EO typical use cases

• WCS is a means for a client to retrieve gridded
  imagery data from a server.
• We can distinguish 3 main use cases for the WCS.
• for retrieving grid geographic data to be used
  for image and vector processing purposes.
• with the increase of geographic data viewer
  skills and functionalities WCS can also be used
  for visualization and data browsing purposes.
• for retrieving a subset of coverage in order to
  save it on a disk and exploit it.
• The Use Case determines the level of metadata
  that is required

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WCS used for EO chained processing

• Use Case A WCS used for EO chained processing
• Processing may concern
• DEM computation
• Geo referencing and/or ortho-rectifcation
• image processing raster/vector processing
  classification filtering
• thematic processing including the use of
  additional vector data
• These applications do require the following
  metadata
• sensor attitude
• original data source in case of elaborated EO
  products
• additional simultaneous observations (clouds) or
  reference to auxiliary data used for producing
  the data (DEM)
• Typical use
• The client requests a large portion of the
  coverage once and apply the processing on this
  portion of the coverage.
• The server would transfer a large amount of data
  per request but might be solicited rarely

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WCS used for file downloading and saving

• Use Case C WCS used for file downloading and
  saving
• This use case reflects the use of the Web
  Coverage Service for downloading the imagery with
  unknown a posteriori use.
• A typical use is the referencing of data source
  in a CS-W catalog response.
• he only WCS request that would be used for this
  use case would be the GetCoverage request.
• In this use case all available information that
  may be required for any possible future use must
  be included.
• This use case is similar to use case A

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WCS used for coverage viewing and display

• Use Case B WCS used for coverage viewing and
  display
• Two possible scenario
• The WCS client may download the image in its
  highest resolution in one go from the server
• optionally in a set of tiles cache this on disk
  and then use this locally cached image for
  displaying.
• The WCS client will make use of the functionality
  to subset the coverage by only requesting the
  data for the required view
• by specifying the Bounding box the width and
  height (in pixel coordinates)
• only the data required for displaying the
  geographical extent is downloaded.
• But this also means that each change of visible
  extent by viewing and panning creates a new Web
  Coverage Service request.
• the data downloaded per coverage request will be
  small but depending on the number of client
  request there may be cumulative high volume of
  transfer from the server

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GMLJP2 Specification

• OGC 05-047r3 OpenGIS encoding specification
• Specifies how geographic imagery should be
  encoded in JPEG2000 a wavelet based encoding for
  imagery
• By including image meta-information encoded
  within GML
• Georeferencing information (gmlRectifiedGrid
  coverages )
• Radiometry (gmlrangeSet)
• Mapping of Geometry to values to JPEG2000
  codestream
• Metadata
• Geographic features (gmlfeatures)
• Annotations (Annotation GML application Schema)
• CRS and UOM definitions
• Styling (SLD GML Default Styling XSLT scripts)
• Single/multiple georeferenced images
  of same or different type DTMs...

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WCS GMLJP2 for use case B

• Viewing purposes (fat client rich thin client)
• Streaming (JPIP)
• Scalability (tiling and multiple resolution)
• Lossless and lossy compression (accuracy)
• Data encryption (security)
• The client would request small portions of the
  coverage and repeat these requests for building
  the tiled view

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WCS GMLJP2 usage for EO

• WCS GMLJP2
• The WCS must define the GMLJP2 as an output
  format either in the description of the service
  or in the description of the coverage.
• It would be useful to introduce the metadata
  level concept either in the description of the
  service or the description of the coverage and in
  the parameters used for requesting data.
• WCS GMLJP2 and JPIP
• JPIP and WCS must be considered as complementary
  protocols.
• The first JPIP request start on WCS and then
  after the client and server operate only on JPIP
  protocol

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WCS GMLJP2 Prototype
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WCS Server prototype

• The GML/JP2 Façade Introduction
• The gateway approach was chosen for several
  reasons
• Ease of implementation compared to implementing
  a full subsetting/resampling engine from
  scratch Possibility to leverage on existing
  WCS implementations
• Possibility to connect it to any remote OGC
  compliant WCS implementation (here we used an
  IONIC product)
• GML Rectified grid can easily be inserted by the
  gateway after the imagery is generated by the
  underlying server thanks to the JP2 file
  structure
• The insertion can be done in a streaming fashion
  so as to not add any latency to the process

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The GML/JP2 Façade GetCoverage
WCS Server prototype

• Client connects to the Spotimage WCS which is
  just a gateway to a full WCS implementation
  responsible for extracting the coverage subset
  (here an IONIC product).

SpotimageWCS
GetCoverage(KVP POST or SOAP)
GetCoverage KVP
Response GML/JP2 Stream
Response JP2 Stream
IONICWCS
Insert GML RectifiedGrid

• The Spot WCS gets the imagery from the underlying
  WCS. It only generates the Rectified Grid XML
  and inserts it properly in the JP2 stream (using
  JPX nested Boxes).

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The GML/JP2 Façade GetCapabilities
DescribeCoverage
WCS Server prototype

• GetCapabilities and DescribeCoverage Operations
  are simply forwarded to the underlying WCS.

SpotimageWCS
GetCapabilities(KVP POST or SOAP)
GetCapabilities KVP
Response XML
Response XML
IONICWCS
SpotimageWCS
DescribeCoverage(KVP POST or SOAP)
DescribeCoverage KVP
Response XML
Response XML
IONICWCS
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Objective extend the SSE WebMapViewer WCS client
with Prototype Support for GMLJP2
GMLJP2 WCS Client
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GMLJP2 Handler
GMLJP2 WCS Client

• Reads JPEG2000 file gtNeed a JP2/JPX codex
• Extracts GML encoded Metadata
• Use Gmlcoverage for geolocation of image
• Extracts metadata and provides a link to the XML
• Extracts Simple GML Features and applies SLD
• Decodes JPEG2000 image

• Use JasPer for image decoding
• Use own code (built around Jai)
• for dealing with metadata

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Test Case 1 GMLJP2 Files
GMLJP2 WCS Client
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Test Case 2 SPOT Image WCS Server
GMLJP2 WCS Client
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Status and conclusion

• HMA-T project status Currently performing last
  client-server integration phase
• Conclusion
• GMLJP2 WCS is promising for EO usage
• Using Open Standards offers interoperability
  perspectives
• JPEG2000 possibilities for image compression
• Possibility to include mask or feature layers
  inside image file
• Retrieve different metadata for different
  purposes
• Full metadata via WCS describecoverage ( 3MB for
  SPOT in DIMAP format)
• Limited metadata for georeferencing and spectral
  information inside GMLJP2
• Feed experience back into OGC Revision working
  Groups for WCS and GMLJP2
• Future work JPIP WCS for EO usage