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°).