[jira] [Commented] (SIS-486) Some map projections produce wrong results when |Δλ| > 180°

["Martin Desruisseaux (Jira)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/SIS-486?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=17001735#comment-17001735 ] 

Martin Desruisseaux commented on SIS-486:
-----------------------------------------

Fixed on {{geoapi-4.0}} branch (not yet merged to master).

> Some map projections produce wrong results when |Δλ| > 180°
> -----------------------------------------------------------
>
>                 Key: SIS-486
>                 URL: https://issues.apache.org/jira/browse/SIS-486
>             Project: Spatial Information Systems
>          Issue Type: Task
>          Components: Referencing
>    Affects Versions: 0.8, 1.0
>            Reporter: Martin Desruisseaux
>            Assignee: Martin Desruisseaux
>            Priority: Major
>             Fix For: 1.1
>
>
> Some map projections produce a wrong result when the difference Δλ between the longitude value and the central meridian is greater than 180°. For most map projections there is no problem because the Δλ value is used directly in trigonometric functions which perform automatically the range reduction for us. For example sin(200°) = sin(-160°). However there is a few map projections where the longitude value is transformed (e.g. multiplied by some factor) _before_ to be given to a trigonometric function. For such map projections, we must apply the range reduction ourselves.
> Impacted map projection methods in Apache SIS 1.0 are:
> * Albers Equal Area (EPSG::9822)
> * Lambert Conic Conformal (EPSG::9801, 9802, 9826)
> * Oblique Stereographic (EPSG::9809)
> * Satellite-Tracking projection
> This problem impacts in particular the cases when one of above projections is used in an area crossing the anti-meridian (±180°).



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