WMS to support publication of slices of a coverage

[Piero Campalani]

The WMS service in rasdaman could allow the publication of 2D slices of coverages as WMS layers. More generally, it could allow any RasQL operation that outputs a 2D array to be applied a priori to a coverage before it is published as WMS layer.

The enhancement request is rooted in ​rasdaman-users::"visualization of sliced 3D coverage using WMS", specifically for enabling the publication of a 2D map inside a 3D cube spatiotemporal collection of maps.

Amongst the ideas that arose in the discussion, one possible way to implement such enhancement could be:

• add a further field in petascopedb::ps_layers to store an optional replacement for the layer label in the RasQL request yielded by Petascope WMS (see Java method petascope.wms.RequestConverter.buildFullImgExp(...)), e.g. rasql_coll:

  petascopedb=# SELECT ps_layers.name, ps_styles.rasqlop, ps_layers.rasql_coll 
  petascopedb-# FROM ps_layers, ps_styles 
  petascopedb-# WHERE ps_styles.layerid=ps_layers.layerid;
      name   |         rasqlop          |    rasql_coll
  -----------+--------------------------+------------------
    standard |  standard * {1c, 1c, 1c} |  img[6,*:*,*:*]
  (1 row)
  

• If ps_layers.rasql_coll <> NULL then Petascope would replace all the labels of the collection in the RasQL query with the rasql_coll string, so that for instance:

  scale(
    extend( img0[0:630,700:1120],[0:630,700:1331] ),
    [0:255,0:255]
  )
  

  would turn to:

  scale(
    extend( (img[6,*:*,*:*])[0:630,700:1120], [0:630,700:1331] ),
    [0:255,0:255]
  )
  

• last and not least, the WMS import utilities [WmsImportTools] in <rasdaman>/applications/rasgeo/wms-import/utilities/ would need to allow the configuration of such new field in the database, as well as to properly select the data in rasdaman for the definition of the WMS metadata (bbox, etc.) and the creation of the pyramid collections.

[Piero Campalani]

As pointed by Alan,
we could as well interface a TIME parameter in the WMS request, following e.g. the handling of time of rasdaman 8.4 (PetascopeTimeHandling#Howrasdaman_8.4handlestime), or as well integrate time with more flexible spatiotemporal CRSs​.

In both cases the WMS import utilities must allow import of 3D cubes of data and the creation of a pyramid of 3D cubes for a layer.

Useful link: MapServer WMS time handling (​http://mapserver.org/ogc/wms_time.html)

[Peter Baumann]

rasql expressions are allowed in the WMS configuration.
Beyond that, WMS does not support such functionality.