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Fixes for webmerc projection (fixes #1078) #1095

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merged 1 commit into from Aug 21, 2018
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Fixes for webmerc projection (fixes #1078) #1095

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12 changes: 8 additions & 4 deletions docs/source/operations/projections/webmerc.rst
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Expand Up @@ -24,9 +24,9 @@ From `Wikipedia <https://en.wikipedia.org/wiki/Web_Mercator>`_:
+---------------------+----------------------------------------------------------+
| **Classification** | Cylindrical (non conformant if used with ellipsoid) |
+---------------------+----------------------------------------------------------+
| **Available forms** | Forward and inverse, spherical projection |
| **Available forms** | Forward and inverse |
+---------------------+----------------------------------------------------------+
| **Defined area** | Global, but best used near the equator |
| **Defined area** | Global |
+---------------------+----------------------------------------------------------+
| **Alias** | webmerc |
+---------------------+----------------------------------------------------------+
Expand All @@ -49,9 +49,13 @@ Example::
Parameters
################################################################################

.. note:: All parameters for the projection are optional.
.. note:: All parameters for the projection are optional, except the ellipsoid
definition, which is WGS84 for the typical use case of EPSG:3857.
In which case, the other parameters are set to their default 0 value.

.. include:: ../options/R.rst
.. include:: ../options/ellps.rst

.. include:: ../options/lon_0.rst

.. include:: ../options/x_0.rst

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10 changes: 2 additions & 8 deletions src/PJ_merc.c
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Expand Up @@ -9,7 +9,7 @@
#include "projects.h"

PROJ_HEAD(merc, "Mercator") "\n\tCyl, Sph&Ell\n\tlat_ts=";
PROJ_HEAD(webmerc, "Web Mercator / Pseudo Mercator") "\n\tCyl, Sph\n\t";
PROJ_HEAD(webmerc, "Web Mercator / Pseudo Mercator") "\n\tCyl, Ell\n\t";

#define EPS10 1.e-10
static double logtanpfpim1(double x) { /* log(tan(x/2 + M_FORTPI)) */
Expand Down Expand Up @@ -92,15 +92,9 @@ PJ *PROJECTION(merc) {

PJ *PROJECTION(webmerc) {

/* Overriding k_0, lat_0 and lon_0 with fixed parameters */
/* Overriding k_0 with fixed parameter */
P->k0 = 1.0;
P->phi0 = 0.0;
P->lam0 = 0.0;

P->b = P->a;
/* Clean up the ellipsoidal parameters to reflect the sphere */
P->es = P->e = P->f = 0;
pj_calc_ellipsoid_params (P, P->a, 0);
P->inv = s_inverse;
P->fwd = s_forward;
return P;
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