Online Data Access using WCS and GMLJP2 Alexandre Robin Spot Image Didier Giacobbo Spot Image Steven - PowerPoint PPT Presentation

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


1
Online Data Access using WCS and
GMLJP2Alexandre Robin Spot ImageDidier
Giacobbo Spot ImageSteven Smolders GIM
2
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

3
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.

4
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)

5
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

6
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

7
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

8
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

9
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

10
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,...

11
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

12
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

13
WCS GMLJP2 Prototype
14
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

15
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).

16
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
17
Objective extend the SSE WebMapViewer WCS client
with Prototype Support for GMLJP2
GMLJP2 WCS Client
18
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

19
Test Case 1 GMLJP2 Files
GMLJP2 WCS Client
20
Test Case 2 SPOT Image WCS Server
GMLJP2 WCS Client
21
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
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