From 6bb14fa874562eb4879a3b80b51b22cd2add058e Mon Sep 17 00:00:00 2001
From: Even Rouault <even.rouault@spatialys.com>
Date: Thu, 27 Dec 2018 16:22:09 +0100
Subject: [PATCH] Add an hardcoded +ellps=GRS80 when there is no
 datum/ellipsoid specification (refs #201)

---
 docs/source/operations/options/ellps.rst |  2 +-
 docs/source/usage/differences.rst        |  5 +--
 src/init.cpp                             | 39 ++++++++++++++++++++++++
 test/gie/ellipsoid.gie                   |  3 +-
 test/unit/gie_self_tests.cpp             |  4 +--
 5 files changed, 47 insertions(+), 6 deletions(-)

diff --git a/docs/source/operations/options/ellps.rst b/docs/source/operations/options/ellps.rst
index af98d377a9..b754f74187 100644
--- a/docs/source/operations/options/ellps.rst
+++ b/docs/source/operations/options/ellps.rst
@@ -2,4 +2,4 @@
 
     See :option:`proj -le` for a list of available ellipsoids.
 
-    *Defaults to "WGS84".*
+    *Defaults to "GRS80".*
diff --git a/docs/source/usage/differences.rst b/docs/source/usage/differences.rst
index 1f7769d312..5694e4d074 100644
--- a/docs/source/usage/differences.rst
+++ b/docs/source/usage/differences.rst
@@ -66,5 +66,6 @@ Removal of proj_def.dat
 -----------------------
 
 Before PROJ 6, the proj_def.dat was used to provide general and per-projection
-parameters, when +no_defs was not specified. It has now been removed. In
-particular, the +ellps=WGS84 is no longer a default.
+parameters, when +no_defs was not specified. It has now been removed. In case,
+no ellipsoid or datum specification is provided in the PROJ string, the
+default ellipsoid is GRS80 (was WGS84 in previous PROJ versions).
diff --git a/src/init.cpp b/src/init.cpp
index 72ed69fe0c..4274f5b460 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -330,6 +330,43 @@ Expand key from buffer or (if not in buffer) from init file
     return init_items;
 }
 
+
+
+static void append_default_ellipsoid_to_paralist (paralist *start) {
+    if (nullptr==start)
+        return;
+
+    /* Set defaults, unless inhibited (either explicitly through a "no_defs" token */
+    /* or implicitly, because we are initializing a pipeline) */
+    if (pj_param_exists (start, "no_defs"))
+        return;
+    auto proj = pj_param_exists (start, "proj");
+    if (nullptr==proj)
+        return;
+    if (strlen (proj->param) < 6)
+        return;
+    if (0==strcmp ("pipeline", proj->param + 5))
+        return;
+
+    /* Don't default ellipse if datum, ellps or any ellipsoid information is set */
+    if  (pj_param_exists (start, "datum"))  return;
+    if  (pj_param_exists (start, "ellps"))  return;
+    if  (pj_param_exists (start, "a"))      return;
+    if  (pj_param_exists (start, "b"))      return;
+    if  (pj_param_exists (start, "rf"))     return;
+    if  (pj_param_exists (start, "f"))      return;
+    if  (pj_param_exists (start, "e"))      return;
+    if  (pj_param_exists (start, "es"))     return;
+
+    /* Locate end of start-list */
+    paralist *last = nullptr;
+    for (last = start;  last->next;  last = last->next);
+
+    /* If we're here, it's OK to append the current default item */
+    last->next = pj_mkparam("ellps=GRS80");
+}
+
+
 /*****************************************************************************/
 static paralist *pj_expand_init_internal(PJ_CONTEXT *ctx, paralist *init, int allow_init_epsg) {
 /******************************************************************************
@@ -594,6 +631,8 @@ pj_init_ctx_with_allow_init_epsg(projCtx ctx, int argc, char **argv, int allow_i
         return nullptr;
     }
 
+    append_default_ellipsoid_to_paralist (start);
+
     /* Allocate projection structure */
     PIN = proj(nullptr);
     if (nullptr==PIN) {
diff --git a/test/gie/ellipsoid.gie b/test/gie/ellipsoid.gie
index 88419346f6..929eb79972 100644
--- a/test/gie/ellipsoid.gie
+++ b/test/gie/ellipsoid.gie
@@ -58,7 +58,8 @@ operation proj=merc +a=-1
 expect    failure errno major_axis_not_given
 
 operation proj=merc
-expect    failure errno major_axis_not_given
+accept    0 0
+expect    0 0
 
 operation proj=merc +es=-1
 expect    failure errno major_axis_not_given
diff --git a/test/unit/gie_self_tests.cpp b/test/unit/gie_self_tests.cpp
index 4e788358f4..9ff7a2789f 100644
--- a/test/unit/gie_self_tests.cpp
+++ b/test/unit/gie_self_tests.cpp
@@ -500,9 +500,9 @@ TEST(gie, io_predicates) {
     ASSERT_FALSE(proj_angular_output(P, PJ_FWD));
     ASSERT_FALSE(proj_angular_output(P, PJ_INV));
 
-    /* pj_init_ctx should default to WGS84 */
+    /* pj_init_ctx should default to GRS80 */
     ASSERT_EQ(P->a, 6378137.0);
-    ASSERT_EQ(P->f, 1.0 / 298.257223563);
+    ASSERT_EQ(P->f, 1.0 / 298.257222101);
     proj_destroy(P);
 
     /* Test that pj_fwd* and pj_inv* returns NaNs when receiving NaN input */