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| author | Even Rouault <even.rouault@spatialys.com> | 2019-10-13 12:58:53 +0200 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2019-10-13 12:58:53 +0200 |
| commit | 3804eac112da0ec5972f355644376556022e4d8f (patch) | |
| tree | 13241edccee9f06713a0517aed91fd3f8843332a | |
| parent | 2d25faba62c698362597a3537a3fe5c3fc7e781a (diff) | |
| parent | 5620ad90e4f697d00e3b4310dc5315fd577fbb85 (diff) | |
| download | PROJ-3804eac112da0ec5972f355644376556022e4d8f.tar.gz PROJ-3804eac112da0ec5972f355644376556022e4d8f.zip | |
Merge pull request #1653 from rouault/doc_ob_tran
ob_tran doc: fix/clarify semantics of o_lat_p/o_lon_p
| -rw-r--r-- | docs/source/operations/projections/ob_tran.rst | 11 | ||||
| -rw-r--r-- | src/projections/ob_tran.cpp | 4 |
2 files changed, 10 insertions, 5 deletions
diff --git a/docs/source/operations/projections/ob_tran.rst b/docs/source/operations/projections/ob_tran.rst index 378f1333..3a23259d 100644 --- a/docs/source/operations/projections/ob_tran.rst +++ b/docs/source/operations/projections/ob_tran.rst @@ -19,9 +19,10 @@ oblique projection by means of the General Oblique Transformation. The user performs the oblique transformation by selecting the oblique projection ``+proj=ob_tran``, specifying the translation factors, :option:`+o_lat_p`, and :option:`+o_lon_p`, and the projection to be used, :option:`+o_proj`. In the -example of the Fairgrieve projection the latitude and longitude of the pole of -the new coordinates, :math:`\alpha` and :math:`\beta` respectively, are to be placed -at 45°N and 90°W and use the :ref:`moll` projection. Because the central meridian +example of the Fairgrieve projection, the latitude and longitude of the North pole +of the unrotated geographic CRS, :math:`\alpha` and :math:`\beta` respectively, +expressed in the rotated geographic CRS, are to be placed +at 45°N and 90°W and the :ref:`moll` projection is used. Because the central meridian of the translated coordinates will follow the :math:`\beta` meridian it is necessary to translate the translated system so that the Greenwich meridian will pass through the center of the projection by offsetting the central meridian. @@ -50,11 +51,11 @@ New pole .. option:: +o_lat_p=<latitude> - Latitude of new pole for oblique projection. + Latitude of the North pole of the unrotated source CRS, expressed in the rotated geographic CRS. .. option:: +o_lon_p=<longitude> - Longitude of new pole for oblique projection. + Longitude of the North pole of the unrotated source CRS, expressed in the rotated geographic CRS. Rotate about point ................................................................................ diff --git a/src/projections/ob_tran.cpp b/src/projections/ob_tran.cpp index 4ae8dbe7..badc6dd8 100644 --- a/src/projections/ob_tran.cpp +++ b/src/projections/ob_tran.cpp @@ -31,8 +31,10 @@ static PJ_XY o_forward(PJ_LP lp, PJ *P) { /* spheroid */ coslam = cos(lp.lam); sinphi = sin(lp.phi); cosphi = cos(lp.phi); + /* Formula (5-8b) of Snyder's "Map projections: a working manual" */ lp.lam = adjlon(aatan2(cosphi * sin(lp.lam), Q->sphip * cosphi * coslam + Q->cphip * sinphi) + Q->lamp); + /* Formula (5-7) */ lp.phi = aasin(P->ctx,Q->sphip * sinphi - Q->cphip * cosphi * coslam); return Q->link->fwd(lp, Q->link); @@ -62,7 +64,9 @@ static PJ_LP o_inverse(PJ_XY xy, PJ *P) { /* spheroid */ coslam = cos(lp.lam -= Q->lamp); sinphi = sin(lp.phi); cosphi = cos(lp.phi); + /* Formula (5-9) */ lp.phi = aasin(P->ctx,Q->sphip * sinphi + Q->cphip * cosphi * coslam); + /* Formula (5-10b) */ lp.lam = aatan2(cosphi * sin(lp.lam), Q->sphip * cosphi * coslam - Q->cphip * sinphi); } |