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From "Martin Desruisseaux (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (SIS-357) EPSG factory should be able to create geocentric CRS as derived CRS
Date Mon, 15 Oct 2018 17:10:00 GMT

     [ https://issues.apache.org/jira/browse/SIS-357?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Martin Desruisseaux updated SIS-357:
------------------------------------
    Fix Version/s:     (was: 1.0)
                   1.1

> EPSG factory should be able to create geocentric CRS as derived CRS
> -------------------------------------------------------------------
>
>                 Key: SIS-357
>                 URL: https://issues.apache.org/jira/browse/SIS-357
>             Project: Spatial Information Systems
>          Issue Type: Improvement
>          Components: Referencing
>    Affects Versions: 0.7, 0.8
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>            Priority: Minor
>             Fix For: 1.1
>
>
> The {{EPSGDataAccess.createCoordinateReferenceSystem(String)}} queries the EPSG {{"Coordinate
Reference System"}} table with more than 10 columns. Some relevant columns for this tasks
are:
> * {{COORD_REF_SYS_KIND}} (may be "geographic 2D", "geographic 3D", "geocentric", "projected",
_etc._)
> * {{SOURCE_GEOGCRS_CODE}} (EPSG code of a {{GeographicCRS}})
> * {{PROJECTION_CONV_CODE}} (EPSG code of a {{CoordinateOperation}})
> Current {{EPSGDataAccess}} implementation uses the {{SOURCE_GEOGCRS_CODE}} and {{PROJECTION_CONV_CODE}}
columns only if the {{COORD_REF_SYS_KIND}} is {{"projected"}}. But the EPSG database sometime
uses those columns for other kind of CRS. For example with WGS 84 coordinate reference systems:
> * EPSG:4326 (geographic 2D) is derived from EPSG:4979 (geographic 3D) with conversion
EPSG:15593 (geographic3D to geographic2D).
> * EPSG::4979 (geographic 3D) is derived from EPSG::4978 (geocentric) with conversion
EPSG:15592 (geocentric to geographic3D).
> We could modify {{EPSGDataAccess}} as below:
> * Unconditionally build a coordinate operation from {{SOURCE_GEOGCRS_CODE}} and {{PROJECTION_CONV_CODE}}
columns instead than only in the projected CRS case.
> * Above operation is mandatory for projected CRS case, optional for all other.
> * If an operation was found, use it for creating a derived CRS like below:
> {code:java}
> CoordinateOperation op = …,
> CoordinateReferenceSystem base = ...;
> if (op instanceof Conversion && base instanceof SingleCRS) {
>     crs = DefaultDerivedCRS.create(properties, (SingleCRS) base, (Conversion) op, cs);
> }
> {code}
> However we may want to keep _Well Known Text_ (WKT) outputs simple by formatting the
CRS as if it was a non-derived CRS. How to handle that is an open question.



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