Add support for PROJ_AUX_DB environment variable to set the path to o…

…ne or several auxiliary DBs

docs/source/usage/environmentvars.rst

@@ -51,6 +51,18 @@ done by setting the variable with no content::
     :envvar:`PROJ_LIB` to allow for multiple versions of PROJ
     resource files on your system without conflicting.
 
+
+.. envvar:: PROJ_AUX_DB
+
+    .. versionadded:: 8.1.0
+
+    To set the path to one or several auxiliary SQLite3 databases of structure
+    identical to the main ``proj.db`` database and that can contain additional
+    object (CRS, transformation, ...) definitions. If several paths are
+    provided, they must be separated by the colon (:) character on Unix, and
+    on Windows, by the semi-colon (;) character.
+
+
 .. envvar:: PROJ_DEBUG
 
     Set the debug level of PROJ. The default debug level is zero, which results

src/ctx.cpp

@@ -91,13 +91,16 @@ pj_ctx pj_ctx::createDefault()
     ctx.logger = pj_stderr_logger;
     NS_PROJ::FileManager::fillDefaultNetworkInterface(&ctx);
 
-    if( getenv("PROJ_DEBUG") != nullptr )
+    const char* projDebug = getenv("PROJ_DEBUG");
+    if( projDebug != nullptr )
     {
-        if( atoi(getenv("PROJ_DEBUG")) >= -PJ_LOG_TRACE )
-            ctx.debug_level = atoi(getenv("PROJ_DEBUG"));
+        const int debugLevel = atoi(projDebug);
+        if( debugLevel >= -PJ_LOG_TRACE )
+            ctx.debug_level = debugLevel;
         else
             ctx.debug_level = PJ_LOG_TRACE;
     }
+
     return ctx;
 }
 

src/iso19111/factory.cpp

@@ -2482,6 +2482,11 @@ DatabaseContext::DatabaseContext() : d(internal::make_unique<Private>()) {}
  * string for the default rules to locate the default proj.db
  * @param auxiliaryDatabasePaths Path and filename of auxiliary databases.
  * Might be empty.
+ * Starting with PROJ 8.1, if this parameter is an empty array,
+ * the PROJ_AUX_DB environment variable will be used, if set.
+ * It must contain one or several paths. If several paths are
+ * provided, they must be separated by the colon (:) character on Unix, and
+ * on Windows, by the semi-colon (;) character.
  * @param ctx Context used for file search.
  * @throw FactoryException
  */
@@ -2493,9 +2498,21 @@ DatabaseContext::create(const std::string &databasePath,
     auto dbCtxPrivate = dbCtx->getPrivate();
     dbCtxPrivate->open(databasePath, ctx);
     dbCtxPrivate->checkDatabaseLayout(databasePath, std::string());
-    if (!auxiliaryDatabasePaths.empty()) {
-        dbCtxPrivate->attachExtraDatabases(auxiliaryDatabasePaths);
-        dbCtxPrivate->auxiliaryDatabasePaths_ = auxiliaryDatabasePaths;
+    auto auxDbs(auxiliaryDatabasePaths);
+    if (auxDbs.empty()) {
+        const char *auxDbStr = getenv("PROJ_AUX_DB");
+        if (auxDbStr) {
+#ifdef _WIN32
+            const char *delim = ";";
+#else
+            const char *delim = ":";
+#endif
+            auxDbs = split(auxDbStr, delim);
+        }
+    }
+    if (!auxDbs.empty()) {
+        dbCtxPrivate->attachExtraDatabases(auxDbs);
+        dbCtxPrivate->auxiliaryDatabasePaths_ = auxDbs;
     }
     dbCtxPrivate->self_ = dbCtx.as_nullable();
     return dbCtx;

test/cli/testprojinfo

@@ -296,6 +296,15 @@ echo "Testing projinfo --dump-db-structure --output-id HOBU:XXXX EPSG:4326 | tai
 $EXE --dump-db-structure --output-id HOBU:XXXX EPSG:4326 | tail -n 4 >>${OUT}
 echo "" >>${OUT}
 
+echo "Testing PROJ_AUX_DB environment variable" >> ${OUT}
+rm -f tmp_projinfo_aux.db
+$EXE --dump-db-structure --output-id HOBU:XXXX EPSG:4326 | sqlite3 tmp_projinfo_aux.db
+export PROJ_AUX_DB=tmp_projinfo_aux.db
+$EXE HOBU:XXXX >>${OUT}
+unset PROJ_AUX_DB
+rm -f tmp_projinfo_aux.db
+echo "" >>${OUT}
+
 # do 'diff' with distribution results
 echo "diff ${OUT} with testprojinfo_out.dist"
 diff -u ${OUT} ${TEST_CLI_DIR}/testprojinfo_out.dist

test/cli/testprojinfo_out.dist

@@ -1559,3 +1559,34 @@ INSERT INTO metadata VALUES('DATABASE.LAYOUT.VERSION.MINOR',0);
 INSERT INTO geodetic_crs VALUES('HOBU','XXXX','WGS 84','','geographic 2D','EPSG','6422','EPSG','6326',NULL,0);
 INSERT INTO usage VALUES('HOBU','USAGE_GEODETIC_CRS_XXXX','geodetic_crs','HOBU','XXXX','EPSG','1262','EPSG','1183');
 
+Testing PROJ_AUX_DB environment variable
+PROJ.4 string:
++proj=longlat +datum=WGS84 +no_defs +type=crs
+
+WKT2:2019 string:
+GEOGCRS["WGS 84",
+    ENSEMBLE["World Geodetic System 1984 ensemble",
+        MEMBER["World Geodetic System 1984 (Transit)"],
+        MEMBER["World Geodetic System 1984 (G730)"],
+        MEMBER["World Geodetic System 1984 (G873)"],
+        MEMBER["World Geodetic System 1984 (G1150)"],
+        MEMBER["World Geodetic System 1984 (G1674)"],
+        MEMBER["World Geodetic System 1984 (G1762)"],
+        ELLIPSOID["WGS 84",6378137,298.257223563,
+            LENGTHUNIT["metre",1]],
+        ENSEMBLEACCURACY[2.0]],
+    PRIMEM["Greenwich",0,
+        ANGLEUNIT["degree",0.0174532925199433]],
+    CS[ellipsoidal,2],
+        AXIS["geodetic latitude (Lat)",north,
+            ORDER[1],
+            ANGLEUNIT["degree",0.0174532925199433]],
+        AXIS["geodetic longitude (Lon)",east,
+            ORDER[2],
+            ANGLEUNIT["degree",0.0174532925199433]],
+    USAGE[
+        SCOPE["Horizontal component of 3D system."],
+        AREA["World."],
+        BBOX[-90,-180,90,180]],
+    ID["HOBU","XXXX"]]
+