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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SIS-317) On-the-fly Geographic3D ↔ CompoundCRS conversion when parsing/formatting WKT 1
Date Thu, 25 Feb 2016 14:36:18 GMT

     [ https://issues.apache.org/jira/browse/SIS-317?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Martin Desruisseaux updated SIS-317:
------------------------------------
    Summary: On-the-fly Geographic3D ↔ CompoundCRS conversion when parsing/formatting WKT
1  (was: On-the-fly Geographic3D ↔ CompoundCRS conversion when formatting WKT 1)

> On-the-fly Geographic3D ↔ CompoundCRS conversion when parsing/formatting WKT 1
> ------------------------------------------------------------------------------
>
>                 Key: SIS-317
>                 URL: https://issues.apache.org/jira/browse/SIS-317
>             Project: Spatial Information Systems
>          Issue Type: Improvement
>          Components: Referencing
>    Affects Versions: 0.6
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>              Labels: WKT
>             Fix For: 0.7
>
>
> According the ISO 19111 standard, ellipsoidal heights can not be represented by standalone
{{VerticalCRS}} instances. Instead they need to be part of a three-dimensional {{GeographicCRS}}
instance. Version 2 of Well Known Text (WKT) format follows this specification, but version
1 had a different model. In WKT 1, three-dimensional {{GeographicCRS}} did not existed (it
is not even possible to represent such CRS in WKT 1 because of heterogeneous units of measurement).
Instead, WKT 1 used a {{CompoundCRS}} made of a two-dimensional {{GeographicCRS}} followed
by a {{VerticalCRS}}.
> *Example (WKT 2 format):*
> {noformat}
> GEODCRS[“WGS 84 (3D)”,
>   DATUM[“World Geodetic System 1984”,
>     ELLIPSOID[“WGS84”, 6378137.0, 298.257223563, LENGTHUNIT[“metre”, 1]]],
>     PRIMEM[“Greenwich”, 0.0, ANGLEUNIT[“degree”, 0.017453292519943295]],
>   CS[ellipsoidal, 3],
>     AXIS[“Longitude (L)”, east, ORDER[1], ANGLEUNIT[“degree”, 0.017453292519943295]],
>     AXIS[“Latitude (B)”, north, ORDER[2], ANGLEUNIT[“degree”, 0.017453292519943295]],
>     AXIS[“Ellipsoidal height (h)”, up, ORDER[3], LENGTHUNIT[“metre”, 1]],
>   AREA[“World”],
>   BBOX[-90.00, -180.00, 90.00, 180.00]]
> {noformat}
> *Same example than above, but using WKT 1 format:*
> {noformat}
> COMPD_CS[“WGS 84 (3D)”,
>   GEOGCS[“WGS 84”,
>     DATUM[“World Geodetic System 1984”,
>       SPHEROID[“WGS84”, 6378137.0, 298.257223563]],
>       PRIMEM[“Greenwich”, 0.0],
>     UNIT[“degree”, 0.017453292519943295],
>     AXIS[“Longitude”, EAST],
>     AXIS[“Latitude”, NORTH]],
>   VERT_CS[“Ellipsoidal height”,
>     VERT_DATUM[“Ellipsoid”, 2002],
>     UNIT[“metre”, 1],
>     AXIS[“Ellipsoidal height”, UP]]]
> {noformat}
> The WKT 1 structure is illegal in today's model, so we need to create it temporarily
only during WKT 1 formatting and discard it immediately after. Conversely, the WKT parser
needs to convert the above-cited {{CompoundCRS}} to a three-dimensional {{GeographicCRS}}
on-the-fly.



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