From a99d94e5aa0051120f7ac38815821e324d866017 Mon Sep 17 00:00:00 2001
From: Nyall Dawson <nyall.dawson@gmail.com>
Date: Fri, 29 Nov 2019 08:43:17 +1000
Subject: [PATCH] On proj6 builds, never apply a lossy conversion from WKT to
 proj strings when attempting to identify a CRS specified via WKT

Because:
1. Proj string conversion is lossy, so we will end up with misleading results
2. If proj can't identify the CRS based on the WKT alone, then any CRS it
identifies from a lossy proj conversion will be incorrect
3. Proj is smarter than QGIS, we should trust it and not rely on downstream hacks

(4. I want to implement creation of user CRS via WKT instead of only proj, and
having this hack in place will break things)
---
 src/core/qgscoordinatereferencesystem.cpp | 29 +++++------------------
 1 file changed, 6 insertions(+), 23 deletions(-)

diff --git a/src/core/qgscoordinatereferencesystem.cpp b/src/core/qgscoordinatereferencesystem.cpp
index 9de8afdf12c..9cdad2b0af7 100644
--- a/src/core/qgscoordinatereferencesystem.cpp
+++ b/src/core/qgscoordinatereferencesystem.cpp
@@ -784,12 +784,13 @@ bool QgsCoordinateReferenceSystem::createFromWkt( const QString &wkt )
 #if PROJ_VERSION_MAJOR>=6
   if ( d->mPj )
   {
+    // try 1 - maybe we can directly grab the auth name and code from the crs already?
     QString authName( proj_get_id_auth_name( d->mPj.get(), 0 ) );
     QString authCode( proj_get_id_code( d->mPj.get(), 0 ) );
 
     if ( authName.isEmpty() || authCode.isEmpty() )
     {
-      // try 2, use proj's identify method and see if there's a nice (singular) candidate we can use
+      // try 2, use proj's identify method and see if there's a nice candidate we can use
       QgsProjUtils::identifyCrs( d->mPj.get(), authName, authCode );
     }
 
@@ -818,29 +819,11 @@ bool QgsCoordinateReferenceSystem::createFromWkt( const QString &wkt )
   }
 #endif
 
-  // always morph from esri as it doesn't hurt anything
-  // FW: Hey, that's not right!  It can screw stuff up! Disable
-  //myOgrSpatialRef.morphFromESRI();
+  // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
+  // WARNING - wkt to proj conversion is lossy, hence we DON'T DO THIS on proj 6
+  // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
 
-
-  // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-  // WARNING - wkt to proj conversion is lossy -- we should reevaluate all this logic!!
-  // !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
-
-#if PROJ_VERSION_MAJOR>=6
-  // create the proj4 structs needed for transforming
-  if ( d->mPj )
-  {
-    const QString proj4String = getFullProjString( d->mPj.get() );
-    if ( !proj4String.isEmpty() )
-    {
-      //now that we have the proj4string, delegate to createFromProj4 so
-      // that we can try to fill in the remaining class members...
-      //create from Proj will set the isValidFlag
-      createFromProj4( proj4String );
-    }
-  }
-#else
+#if PROJ_VERSION_MAJOR<6
   // create the proj4 structs needed for transforming
   char *proj4src = nullptr;
   OSRExportToProj4( d->mCRS, &proj4src );