= Time dimension(s) handling in ''Petascope'' =

The incoming `rasdaman 8.4` release will represent a watershed-release with respect to how ''Petascope'' handles time and more generally on how ''Petascope'' manages the coordinate reference systems of the coverages. That said, two separate sections are provided here to give guidance from both client and server viewpoint ''before'' and ''after'' the `8.4` release.


[[span(NOTE: ''No improvements or feature changes will be applied for maintenance of the 8.4 release.'', style=color: Black; font-size: 80%, id=git)]]


== How `rasdaman_8.4` handles time ==

A temporal dimension is used to integrate time into the [https://portal.opengeospatial.org/modules/admin/license_agreement.php?suppressHeaders=0&access_license_id=3&target=http://portal.opengeospatial.org/files/?artifact_id=41438 coverage model] in case of series of spatial datasets. [[BR]]
__'''Dates'''__ in ''WCS !GetCoverage'' subsettings are currently supported in the format 
`"`'''[[span(`t(YYYY-MM-DD[,YYYY-MM-DD])`, style=color: DodgerBlue; font-size: 90%)]]'''`"` 
on a temporal axis.

Finer temporal resolutions (hour, minutes, etc.) or irregular time spacing are __not__ supported, however ''N''-days resolution are accepted.

A KVP ''!GetCoverage'' example:
{{{
#!div style="background: GhostWhite; border: 5px ridge; text-align: center; width: 70%; margin-left: auto ; margin-right: auto ;" 
{{{
#!html
<h2>...&service=WCS&request=GetCoverage&<u><span style="color: MediumBlue;">subset=<span style="color: DodgerBlue;">t</span>(2010-06-19)</span></u>&...</h2>
}}}
}}}


A temporal axis is thus recognized by ''Petascope'' by its 
"'''[[span(`t`, style=color: DodgerBlue; font-size: 90%)]]'''" label (binding the label in the request subset and the value in 
[[span(`petascopedb::ps_domain.name`, style=color: IndianRed; font-size: 90%)]]), on which it assumes its `rasdaman` grid indexes are [http://en.wikipedia.org/wiki/Julian_day#Alternatives ANSI date] numbers. [[BR]]
The `gml:RectifiedGridCoverage` of a response including a time-dimension fills temporal coordinates with ANSI integers at the domain ''"external CRS"'' level (e.g. `gml:offsetVector`, `gml:boundedBy`), and `rasdaman` indexes at the grid level (`gml:GridEnvelope`). [[BR]]
Direct grid indexes can as well be directly set in the WCS request by forcing the "CRS:1" coordinate system (the current label for the internal grid-CRS of a coverage), like: "[[span(`...subset=t,CRS:1(0,10)...`), style=color: DarkBlue; font-size: 90%)]]".

The recommended setup for enabling such behavior in ''Petascope'' is to:

 * have a regular time axis labeled __''t''__;
 * set the CRS associated with the temporal axis to some __CRS≠"CRS:1"__ (the current label for the internal grid-CRS of a coverage);
 * set proper ANSI bounds in [[span(`petascopedb::ps_domain`, style=color: IndianRed; font-size: 90%)]]: the ratio between these bounds and the `sdom` along the temporal dimension in `rasdaman` will determine the resolution.

Alternatively, a user could define own out of band time management by either:
 * publishing temporal metadata inside the [[span(`gmlcov:metadata`, style=color: SeaGReen; font-size: 90%)]] of a ''WCS !DescribeCoverage'' response;
 * manage time entirely ''"in house"''.

The features in future releases are going to provide custom temporal resolutions with regular/irregular spacing, by implementing a new design for the management of spatiotemporal CRSs, and supporting the new [[span(`GML 3.3`, style=color: SeaGReen; font-size: 90%)]] [https://portal.opengeospatial.org/files/?artifact_id=46568 referenceable grids]. See next section for further insight.

== Ongoing development (towards `rasdaman_9.0`) ==

See [attachment:TemporalCRSs.pdf slides] for first concepts and examples.

{{{
#!comment
HTML colors: http://www.w3schools.com/html/html_colornames.asp
}}}