• Use case: Download false-color image, then perform on-the-fly computation of the Normalized Difference Vegetation Index (NDVI)
• Dataset: ICGC False-Color Orthoimage; coverage created from GeoTIFF and separate XML file with INSPIRE metadata
• Service used: OGC WCPS
• Notes: The false-color image can be subset and downloaded via WCS GetCoverage or via WCPS. However, WCPS additionally allows pixel-wise computation, such as the NDVI. WCPS queries like this typically are generated automatically by some client or script, users will not notice them.

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https://inspire.rasdaman.org/rasdaman/ows?

    service=WCS & version=2.0.1 &

    request=GetCoverage & coverageId=INSPIRE_OI_IR &

    subset=E(480000,482000) & subset=N(4651150,4652100) &

    format=image/jpeg    

Next, we do the same with WCPS - just subsetting:

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for $ir in (INSPIRE_OI_IR)

return

  encode(

    $ir[ E(480000:482000), N(4651150:4652100) ],

    "image/jpeg"

  )               

Finally, we compute the NDVI. For better visualization, the NDVI value (normally between -1 and +1) gets added 1 (to be non-negative) and multiplied with 127 (to "stretch" it into the 0 to 255 range of 8-bit grayscale imagery). Cast operations (syntactically: data types in parenthesis, like "(unsigned char)") first force the integer values from the coverage into float for the division, and then into the target format of 8-bit unsigned quantities.

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for $ir in (INSPIRE_OI_IR)

return

  encode(

    (unsigned char) (127 * ( 1 + ((float) $ir.red - $ir.green) / ((float) $ir.red + $ir.green) ) ) 

    [ E(480000:482000), N(4651150:4652100) ],

    "image/jpeg"

  )