Merge pull request #1217 from rouault/remove_proj_5_crs_export

ISO19111: remove PROJ.5 specific format for CRS (refs #1214)

4 files changed, 148 insertions, 215 deletions

diff --git a/src/apps/projinfo.cpp b/src/apps/projinfo.cpp
index b418bc57..446a1e9e 100644
--- a/src/apps/projinfo.cpp
+++ b/src/apps/projinfo.cpp
@@ -61,7 +61,6 @@ namespace { // anonymous namespace
 struct OutputOptions {
     bool quiet = false;
     bool PROJ5 = false;
-    bool PROJ4 = false;
     bool WKT2_2018 = false;
     bool WKT2_2018_SIMPLIFIED = false;
     bool WKT2_2015 = false;
@@ -100,7 +99,7 @@ static void usage() {
         << std::endl;
     std::cerr << std::endl;
     std::cerr << "-o: formats is a comma separated combination of: "
-                 "all,default,PROJ4,PROJ,WKT_ALL,WKT2_2015,WKT2_2018,WKT1_GDAL,"
+                 "all,default,PROJ,WKT_ALL,WKT2_2015,WKT2_2018,WKT1_GDAL,"
                  "WKT1_ESRI"
               << std::endl;
     std::cerr << "    Except 'all' and 'default', other format can be preceded "
@@ -256,32 +255,18 @@ static void outputObject(DatabaseContextPtr dbContext, BaseObjectNNPtr obj,
     if (projStringExportable) {
         if (outputOpt.PROJ5) {
             try {
-                if (!outputOpt.quiet) {
-                    std::cout << "PROJ string:" << std::endl;
-                }
-                std::cout << projStringExportable->exportToPROJString(
-                                 PROJStringFormatter::create(
-                                     PROJStringFormatter::Convention::PROJ_5,
-                                     dbContext)
-                                     .get())
-                          << std::endl;
-            } catch (const std::exception &e) {
-                std::cerr << "Error when exporting to PROJ string: " << e.what()
-                          << std::endl;
-            }
-            alreadyOutputed = true;
-        }
-
-        if (outputOpt.PROJ4) {
-            try {
                 if (alreadyOutputed) {
                     std::cout << std::endl;
                 }
+                auto crs = nn_dynamic_pointer_cast<CRS>(obj);
                 if (!outputOpt.quiet) {
-                    std::cout << "PROJ.4 string:" << std::endl;
+                    if( crs ) {
+                        std::cout << "PROJ.4 string:" << std::endl;
+                    } else {
+                        std::cout << "PROJ string:" << std::endl;
+                    }
                 }
 
-                auto crs = nn_dynamic_pointer_cast<CRS>(obj);
                 std::shared_ptr<IPROJStringExportable> objToExport;
                 if (crs) {
                     objToExport =
@@ -295,7 +280,7 @@ static void outputObject(DatabaseContextPtr dbContext, BaseObjectNNPtr obj,
 
                 std::cout << objToExport->exportToPROJString(
                                  PROJStringFormatter::create(
-                                     PROJStringFormatter::Convention::PROJ_4,
+                                     PROJStringFormatter::Convention::PROJ_5,
                                      dbContext)
                                      .get())
                           << std::endl;
@@ -651,23 +636,15 @@ int main(int argc, char **argv) {
             for (auto format : formats) {
                 if (ci_equal(format, "all")) {
                     outputOpt.PROJ5 = true;
-                    outputOpt.PROJ4 = true;
                     outputOpt.WKT2_2018 = true;
                     outputOpt.WKT2_2015 = true;
                     outputOpt.WKT1_GDAL = true;
                     outputOpt.WKT1_ESRI = true;
                 } else if (ci_equal(format, "default")) {
                     outputOpt.PROJ5 = true;
-                    outputOpt.PROJ4 = false;
                     outputOpt.WKT2_2018 = false;
                     outputOpt.WKT2_2015 = true;
                     outputOpt.WKT1_GDAL = false;
-                } else if (ci_equal(format, "PROJ4") ||
-                           ci_equal(format, "PROJ.4")) {
-                    outputOpt.PROJ4 = true;
-                } else if (ci_equal(format, "-PROJ4") ||
-                           ci_equal(format, "-PROJ.4")) {
-                    outputOpt.PROJ4 = false;
                 } else if (ci_equal(format, "PROJ")) {
                     outputOpt.PROJ5 = true;
                 } else if (ci_equal(format, "-PROJ")) {
@@ -929,7 +906,7 @@ int main(int argc, char **argv) {
     }
 
     if (outputOpt.quiet &&
-        (outputOpt.PROJ5 + outputOpt.PROJ4 + outputOpt.WKT2_2018 +
+        (outputOpt.PROJ5 + outputOpt.WKT2_2018 +
          outputOpt.WKT2_2015 + outputOpt.WKT1_GDAL) != 1) {
         std::cerr << "-q can only be used with a single output format"
                   << std::endl;
diff --git a/src/iso19111/coordinateoperation.cpp b/src/iso19111/coordinateoperation.cpp
index d00be93f..47f10392 100644
--- a/src/iso19111/coordinateoperation.cpp
+++ b/src/iso19111/coordinateoperation.cpp
@@ -5377,8 +5377,8 @@ bool Conversion::addWKTExtensionNode(io::WKTFormatter *formatter) const {
         bool north = true;
         if (l_method->getPrivate()->projMethodOverride_ == "etmerc" &&
             !isUTM(zone, north)) {
-            auto projFormatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_4);
+            auto projFormatter = io::PROJStringFormatter::create();
+            projFormatter->setCRSExport(true);
             projFormatter->setUseETMercForTMerc(true);
             formatter->startNode(io::WKTConstants::EXTENSION, false);
             formatter->addQuotedString("PROJ4");
@@ -5391,8 +5391,8 @@ bool Conversion::addWKTExtensionNode(io::WKTFormatter *formatter) const {
                        EPSG_CODE_METHOD_POPULAR_VISUALISATION_PSEUDO_MERCATOR ||
                    nameStr() == "Popular Visualisation Mercator") {
 
-            auto projFormatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_4);
+            auto projFormatter = io::PROJStringFormatter::create();
+            projFormatter->setCRSExport(true);
             if (createPROJ4WebMercator(this, projFormatter.get())) {
                 formatter->startNode(io::WKTConstants::EXTENSION, false);
                 formatter->addQuotedString("PROJ4");
@@ -5401,8 +5401,8 @@ bool Conversion::addWKTExtensionNode(io::WKTFormatter *formatter) const {
                 return true;
             }
         } else if (starts_with(methodName, "PROJ ")) {
-            auto projFormatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_4);
+            auto projFormatter = io::PROJStringFormatter::create();
+            projFormatter->setCRSExport(true);
             if (createPROJExtensionFromCustomProj(this, projFormatter.get(),
                                                   true)) {
                 formatter->startNode(io::WKTConstants::EXTENSION, false);
@@ -5413,8 +5413,8 @@ bool Conversion::addWKTExtensionNode(io::WKTFormatter *formatter) const {
             }
         } else if (methodName ==
                    PROJ_WKT2_NAME_METHOD_GEOSTATIONARY_SATELLITE_SWEEP_X) {
-            auto projFormatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_4);
+            auto projFormatter = io::PROJStringFormatter::create();
+            projFormatter->setCRSExport(true);
             formatter->startNode(io::WKTConstants::EXTENSION, false);
             formatter->addQuotedString("PROJ4");
             _exportToPROJString(projFormatter.get());
@@ -5445,12 +5445,10 @@ void Conversion::_exportToPROJString(
     const bool applySourceCRSModifiers =
         !isZUnitConversion && !isAffineParametric &&
         !isAxisOrderReversal(methodEPSGCode) && !isGeographicGeocentric;
-    const bool applyTargetCRSModifiers = applySourceCRSModifiers;
+    bool applyTargetCRSModifiers = applySourceCRSModifiers;
 
     auto l_sourceCRS = sourceCRS();
-    if (l_sourceCRS && applySourceCRSModifiers &&
-        formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_5) {
+    if (!formatter->getCRSExport() && l_sourceCRS && applySourceCRSModifiers) {
         auto geogCRS =
             dynamic_cast<const crs::GeographicCRS *>(l_sourceCRS.get());
         if (geogCRS) {
@@ -5593,8 +5591,7 @@ void Conversion::_exportToPROJString(
                 EPSG_NAME_PARAMETER_LATITUDE_OF_NATURAL_ORIGIN);
         }
         // PROJ.4 specific hack for webmercator
-    } else if (formatter->convention() ==
-                   io::PROJStringFormatter::Convention::PROJ_4 &&
+    } else if (formatter->getCRSExport() &&
                methodEPSGCode ==
                    EPSG_CODE_METHOD_POPULAR_VISUALISATION_PSEUDO_MERCATOR) {
         if (!createPROJ4WebMercator(this, formatter)) {
@@ -5605,14 +5602,15 @@ void Conversion::_exportToPROJString(
         }
         bConversionDone = true;
         bEllipsoidParametersDone = true;
+        applyTargetCRSModifiers = false;
     } else if (ci_equal(convName, "Popular Visualisation Mercator")) {
-        if (formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_4) {
+        if (formatter->getCRSExport()) {
             if (!createPROJ4WebMercator(this, formatter)) {
                 throw io::FormattingException(concat(
                     "Cannot export ", convName,
                     " as PROJ.4 string outside of a ProjectedCRS context"));
             }
+            applyTargetCRSModifiers = false;
         } else {
             formatter->addStep("webmerc");
             if (l_sourceCRS) {
@@ -5717,8 +5715,7 @@ void Conversion::_exportToPROJString(
         if (!bEllipsoidParametersDone) {
             auto targetGeogCRS = l_targetCRS->extractGeographicCRS();
             if (targetGeogCRS) {
-                if (formatter->convention() ==
-                    io::PROJStringFormatter::Convention::PROJ_4) {
+                if (formatter->getCRSExport()) {
                     targetGeogCRS->addDatumInfoToPROJString(formatter);
                 } else {
                     targetGeogCRS->ellipsoid()->_exportToPROJString(formatter);
@@ -5737,13 +5734,10 @@ void Conversion::_exportToPROJString(
         auto derivedGeographicCRS =
             dynamic_cast<const crs::DerivedGeographicCRS *>(l_targetCRS.get());
         if (derivedGeographicCRS) {
-            if (formatter->convention() ==
-                io::PROJStringFormatter::Convention::PROJ_5) {
-                auto geogCRS = derivedGeographicCRS->baseCRS();
-                formatter->setOmitProjLongLatIfPossible(true);
-                geogCRS->_exportToPROJString(formatter);
-                formatter->setOmitProjLongLatIfPossible(false);
-            }
+            auto baseGeodCRS = derivedGeographicCRS->baseCRS();
+            formatter->setOmitProjLongLatIfPossible(true);
+            baseGeodCRS->_exportToPROJString(formatter);
+            formatter->setOmitProjLongLatIfPossible(false);
         }
     }
 }
@@ -11104,31 +11098,27 @@ CoordinateOperationFactory::Private::createOperations(
         if (!targetProjExportable) {
             throw InvalidOperation("Target CRS is not PROJ exportable");
         }
-        auto projFormatter = io::PROJStringFormatter::create(
-            io::PROJStringFormatter::Convention::PROJ_4);
+        auto projFormatter = io::PROJStringFormatter::create();
+        projFormatter->setCRSExport(true);
         projFormatter->startInversion();
         sourceProjExportable->_exportToPROJString(projFormatter.get());
-
         auto geogSrc =
             dynamic_cast<const crs::GeographicCRS *>(sourceCRS.get());
         if (geogSrc) {
-            auto proj5Formatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_5);
-            geogSrc->addAngularUnitConvertAndAxisSwap(proj5Formatter.get());
-            projFormatter->ingestPROJString(proj5Formatter->toString());
+            auto tmpFormatter = io::PROJStringFormatter::create();
+            geogSrc->addAngularUnitConvertAndAxisSwap(tmpFormatter.get());
+            projFormatter->ingestPROJString(tmpFormatter->toString());
         }
 
         projFormatter->stopInversion();
 
         targetProjExportable->_exportToPROJString(projFormatter.get());
-
         auto geogDst =
             dynamic_cast<const crs::GeographicCRS *>(targetCRS.get());
         if (geogDst) {
-            auto proj5Formatter = io::PROJStringFormatter::create(
-                io::PROJStringFormatter::Convention::PROJ_5);
-            geogDst->addAngularUnitConvertAndAxisSwap(proj5Formatter.get());
-            projFormatter->ingestPROJString(proj5Formatter->toString());
+            auto tmpFormatter = io::PROJStringFormatter::create();
+            geogDst->addAngularUnitConvertAndAxisSwap(tmpFormatter.get());
+            projFormatter->ingestPROJString(tmpFormatter->toString());
         }
 
         const auto PROJString = projFormatter->toString();
diff --git a/src/iso19111/crs.cpp b/src/iso19111/crs.cpp
index 190291de..6776093a 100644
--- a/src/iso19111/crs.cpp
+++ b/src/iso19111/crs.cpp
@@ -1142,13 +1142,11 @@ void GeodeticCRS::addGeocentricUnitConversionIntoPROJString(
     const auto &unit = axisList[0]->unit();
     if (!unit._isEquivalentTo(common::UnitOfMeasure::METRE,
                               util::IComparable::Criterion::EQUIVALENT)) {
-        if (formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_4) {
-            io::FormattingException::Throw("GeodeticCRS::exportToPROJString(): "
-                                           "non-meter unit not supported for "
-                                           "PROJ.4");
+        if (formatter->getCRSExport()) {
+            io::FormattingException::Throw(
+                "GeodeticCRS::exportToPROJString() only "
+                "supports metre unit");
         }
-
         formatter->addStep("unitconvert");
         formatter->addParam("xy_in", "m");
         formatter->addParam("z_in", "m");
@@ -1164,8 +1162,7 @@ void GeodeticCRS::addGeocentricUnitConversionIntoPROJString(
         const auto &toSI = unit.conversionToSI();
         formatter->addParam("xy_out", toSI);
         formatter->addParam("z_out", toSI);
-    } else if (formatter->convention() ==
-               io::PROJStringFormatter::Convention::PROJ_4) {
+    } else if (formatter->getCRSExport()) {
         formatter->addParam("units", "m");
     }
 }
@@ -1177,14 +1174,11 @@ void GeodeticCRS::addGeocentricUnitConversionIntoPROJString(
 void GeodeticCRS::_exportToPROJString(
     io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
 {
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_4) {
-        const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
-        if (!extensionProj4.empty()) {
-            formatter->ingestPROJString(extensionProj4);
-            formatter->addNoDefs(false);
-            return;
-        }
+    const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
+    if (!extensionProj4.empty()) {
+        formatter->ingestPROJString(extensionProj4);
+        formatter->addNoDefs(false);
+        return;
     }
 
     if (!isGeocentric()) {
@@ -1193,11 +1187,10 @@ void GeodeticCRS::_exportToPROJString(
             "supports geocentric coordinate systems");
     }
 
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_4) {
-        formatter->addStep("geocent");
-    } else {
+    if (!formatter->getCRSExport()) {
         formatter->addStep("cart");
+    } else {
+        formatter->addStep("geocent");
     }
     addDatumInfoToPROJString(formatter);
     addGeocentricUnitConversionIntoPROJString(formatter);
@@ -1214,9 +1207,8 @@ void GeodeticCRS::addDatumInfoToPROJString(
     bool datumWritten = false;
     const auto &nadgrids = formatter->getHDatumExtension();
     const auto &l_datum = datum();
-    if (formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_4 &&
-        l_datum && TOWGS84Params.empty() && nadgrids.empty()) {
+    if (formatter->getCRSExport() && l_datum && TOWGS84Params.empty() &&
+        nadgrids.empty()) {
         if (l_datum->_isEquivalentTo(
                 datum::GeodeticReferenceFrame::EPSG_6326.get(),
                 util::IComparable::Criterion::EQUIVALENT)) {
@@ -1857,57 +1849,53 @@ void GeographicCRS::addAngularUnitConvertAndAxisSwap(
     io::PROJStringFormatter *formatter) const {
     const auto &axisList = coordinateSystem()->axisList();
 
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_5) {
-
-        formatter->addStep("unitconvert");
-        formatter->addParam("xy_in", "rad");
-        if (axisList.size() == 3 && !formatter->omitZUnitConversion()) {
-            formatter->addParam("z_in", "m");
-        }
-        {
-            const auto &unitHoriz = axisList[0]->unit();
-            const auto projUnit = unitHoriz.exportToPROJString();
-            if (projUnit.empty()) {
-                formatter->addParam("xy_out", unitHoriz.conversionToSI());
-            } else {
-                formatter->addParam("xy_out", projUnit);
-            }
+    formatter->addStep("unitconvert");
+    formatter->addParam("xy_in", "rad");
+    if (axisList.size() == 3 && !formatter->omitZUnitConversion()) {
+        formatter->addParam("z_in", "m");
+    }
+    {
+        const auto &unitHoriz = axisList[0]->unit();
+        const auto projUnit = unitHoriz.exportToPROJString();
+        if (projUnit.empty()) {
+            formatter->addParam("xy_out", unitHoriz.conversionToSI());
+        } else {
+            formatter->addParam("xy_out", projUnit);
         }
-        if (axisList.size() == 3 && !formatter->omitZUnitConversion()) {
-            const auto &unitZ = axisList[2]->unit();
-            auto projVUnit = unitZ.exportToPROJString();
-            if (projVUnit.empty()) {
-                formatter->addParam("z_out", unitZ.conversionToSI());
-            } else {
-                formatter->addParam("z_out", projVUnit);
-            }
+    }
+    if (axisList.size() == 3 && !formatter->omitZUnitConversion()) {
+        const auto &unitZ = axisList[2]->unit();
+        auto projVUnit = unitZ.exportToPROJString();
+        if (projVUnit.empty()) {
+            formatter->addParam("z_out", unitZ.conversionToSI());
+        } else {
+            formatter->addParam("z_out", projVUnit);
         }
+    }
 
-        const char *order[2] = {nullptr, nullptr};
-        const char *one = "1";
-        const char *two = "2";
-        for (int i = 0; i < 2; i++) {
-            const auto &dir = axisList[i]->direction();
-            if (&dir == &cs::AxisDirection::WEST) {
-                order[i] = "-1";
-            } else if (&dir == &cs::AxisDirection::EAST) {
-                order[i] = one;
-            } else if (&dir == &cs::AxisDirection::SOUTH) {
-                order[i] = "-2";
-            } else if (&dir == &cs::AxisDirection::NORTH) {
-                order[i] = two;
-            }
-        }
-        if (order[0] && order[1] && (order[0] != one || order[1] != two)) {
-            formatter->addStep("axisswap");
-            char orderStr[10];
-            strcpy(orderStr, order[0]);
-            strcat(orderStr, ",");
-            strcat(orderStr, order[1]);
-            formatter->addParam("order", orderStr);
+    const char *order[2] = {nullptr, nullptr};
+    const char *one = "1";
+    const char *two = "2";
+    for (int i = 0; i < 2; i++) {
+        const auto &dir = axisList[i]->direction();
+        if (&dir == &cs::AxisDirection::WEST) {
+            order[i] = "-1";
+        } else if (&dir == &cs::AxisDirection::EAST) {
+            order[i] = one;
+        } else if (&dir == &cs::AxisDirection::SOUTH) {
+            order[i] = "-2";
+        } else if (&dir == &cs::AxisDirection::NORTH) {
+            order[i] = two;
         }
     }
+    if (order[0] && order[1] && (order[0] != one || order[1] != two)) {
+        formatter->addStep("axisswap");
+        char orderStr[10];
+        strcpy(orderStr, order[0]);
+        strcat(orderStr, ",");
+        strcat(orderStr, order[1]);
+        formatter->addParam("order", orderStr);
+    }
 }
 //! @endcond
 
@@ -1917,14 +1905,11 @@ void GeographicCRS::addAngularUnitConvertAndAxisSwap(
 void GeographicCRS::_exportToPROJString(
     io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
 {
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_4) {
-        const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
-        if (!extensionProj4.empty()) {
-            formatter->ingestPROJString(extensionProj4);
-            formatter->addNoDefs(false);
-            return;
-        }
+    const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
+    if (!extensionProj4.empty()) {
+        formatter->ingestPROJString(extensionProj4);
+        formatter->addNoDefs(false);
+        return;
     }
 
     if (!formatter->omitProjLongLatIfPossible() ||
@@ -1934,8 +1919,9 @@ void GeographicCRS::_exportToPROJString(
         formatter->addStep("longlat");
         addDatumInfoToPROJString(formatter);
     }
-
-    addAngularUnitConvertAndAxisSwap(formatter);
+    if (!formatter->getCRSExport()) {
+        addAngularUnitConvertAndAxisSwap(formatter);
+    }
 }
 //! @endcond
 
@@ -2107,20 +2093,17 @@ void VerticalCRS::addLinearUnitConvert(
     io::PROJStringFormatter *formatter) const {
     auto &axisList = coordinateSystem()->axisList();
 
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_5) {
-        if (!axisList.empty()) {
-            auto projUnit = axisList[0]->unit().exportToPROJString();
-            if (axisList[0]->unit().conversionToSI() != 1.0) {
-                formatter->addStep("unitconvert");
-                formatter->addParam("z_in", "m");
-                auto projVUnit = axisList[0]->unit().exportToPROJString();
-                if (projVUnit.empty()) {
-                    formatter->addParam("z_out",
-                                        axisList[0]->unit().conversionToSI());
-                } else {
-                    formatter->addParam("z_out", projVUnit);
-                }
+    if (!axisList.empty()) {
+        auto projUnit = axisList[0]->unit().exportToPROJString();
+        if (axisList[0]->unit().conversionToSI() != 1.0) {
+            formatter->addStep("unitconvert");
+            formatter->addParam("z_in", "m");
+            auto projVUnit = axisList[0]->unit().exportToPROJString();
+            if (projVUnit.empty()) {
+                formatter->addParam("z_out",
+                                    axisList[0]->unit().conversionToSI());
+            } else {
+                formatter->addParam("z_out", projVUnit);
             }
         }
     }
@@ -2437,14 +2420,6 @@ void DerivedCRS::setDerivingConversionCRS() {
 
 // ---------------------------------------------------------------------------
 
-void DerivedCRS::baseExportToPROJString(
-    io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
-{
-    d->derivingConversion_->_exportToPROJString(formatter);
-}
-
-// ---------------------------------------------------------------------------
-
 void DerivedCRS::baseExportToWKT(io::WKTFormatter *&formatter,
                                  const std::string &keyword,
                                  const std::string &baseKeyword) const {
@@ -2742,17 +2717,14 @@ void ProjectedCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 void ProjectedCRS::_exportToPROJString(
     io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
 {
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_4) {
-        const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
-        if (!extensionProj4.empty()) {
-            formatter->ingestPROJString(extensionProj4);
-            formatter->addNoDefs(false);
-            return;
-        }
+    const auto &extensionProj4 = CRS::getPrivate()->extensionProj4_;
+    if (!extensionProj4.empty()) {
+        formatter->ingestPROJString(extensionProj4);
+        formatter->addNoDefs(false);
+        return;
     }
 
-    baseExportToPROJString(formatter);
+    derivingConversionRef()->_exportToPROJString(formatter);
 }
 
 // ---------------------------------------------------------------------------
@@ -2821,8 +2793,7 @@ void ProjectedCRS::addUnitConvertAndAxisSwap(io::PROJStringFormatter *formatter,
                               util::IComparable::Criterion::EQUIVALENT)) {
         auto projUnit = unit.exportToPROJString();
         const double toSI = unit.conversionToSI();
-        if (formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_5) {
+        if (!formatter->getCRSExport()) {
             formatter->addStep("unitconvert");
             formatter->addParam("xy_in", "m");
             formatter->addParam("z_in", "m");
@@ -2840,17 +2811,11 @@ void ProjectedCRS::addUnitConvertAndAxisSwap(io::PROJStringFormatter *formatter,
                 formatter->addParam("units", projUnit);
             }
         }
-    } else if (formatter->convention() ==
-               io::PROJStringFormatter::Convention::PROJ_4) {
-        // could come from the hardcoded def of webmerc
-        if (!formatter->hasParam("units")) {
-            formatter->addParam("units", "m");
-        }
+    } else if (formatter->getCRSExport()) {
+        formatter->addParam("units", "m");
     }
 
-    if (formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_5 &&
-        !axisSpecFound) {
+    if (!axisSpecFound && !formatter->getCRSExport()) {
         const auto &dir0 = axisList[0]->direction();
         const auto &dir1 = axisList[1]->direction();
         if (!(&dir0 == &cs::AxisDirection::EAST &&
@@ -3792,13 +3757,6 @@ void BoundCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 void BoundCRS::_exportToPROJString(
     io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
 {
-    if (formatter->convention() ==
-        io::PROJStringFormatter::Convention::PROJ_5) {
-        io::FormattingException::Throw(
-            "BoundCRS cannot be exported as a PROJ.5 string, but its baseCRS "
-            "might");
-    }
-
     auto crs_exportable =
         dynamic_cast<const io::IPROJStringExportable *>(d->baseCRS_.get());
     if (!crs_exportable) {
@@ -4086,9 +4044,10 @@ void DerivedGeodeticCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 // ---------------------------------------------------------------------------
 
 void DerivedGeodeticCRS::_exportToPROJString(
-    io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
+    io::PROJStringFormatter *) const // throw(io::FormattingException)
 {
-    baseExportToPROJString(formatter);
+    throw io::FormattingException(
+        "DerivedGeodeticCRS cannot be exported to PROJ string");
 }
 
 // ---------------------------------------------------------------------------
@@ -4223,9 +4182,10 @@ void DerivedGeographicCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 // ---------------------------------------------------------------------------
 
 void DerivedGeographicCRS::_exportToPROJString(
-    io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
+    io::PROJStringFormatter *) const // throw(io::FormattingException)
 {
-    baseExportToPROJString(formatter);
+    throw io::FormattingException(
+        "DerivedGeographicCRS cannot be exported to PROJ string");
 }
 
 // ---------------------------------------------------------------------------
@@ -4377,14 +4337,6 @@ void DerivedProjectedCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 
 // ---------------------------------------------------------------------------
 
-void DerivedProjectedCRS::_exportToPROJString(
-    io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
-{
-    baseExportToPROJString(formatter);
-}
-
-// ---------------------------------------------------------------------------
-
 bool DerivedProjectedCRS::_isEquivalentTo(
     const util::IComparable *other,
     util::IComparable::Criterion criterion) const {
@@ -4792,9 +4744,10 @@ void DerivedVerticalCRS::_exportToWKT(io::WKTFormatter *formatter) const {
 // ---------------------------------------------------------------------------
 
 void DerivedVerticalCRS::_exportToPROJString(
-    io::PROJStringFormatter *formatter) const // throw(io::FormattingException)
+    io::PROJStringFormatter *) const // throw(io::FormattingException)
 {
-    baseExportToPROJString(formatter);
+    throw io::FormattingException(
+        "DerivedVerticalCRS cannot be exported to PROJ string");
 }
 
 // ---------------------------------------------------------------------------
diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index cfccd70f..13a8f236 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -4596,15 +4596,19 @@ IPROJStringExportable::~IPROJStringExportable() = default;
 
 std::string IPROJStringExportable::exportToPROJString(
     PROJStringFormatter *formatter) const {
+    const bool bIsCRS = dynamic_cast<const crs::CRS *>(this) != nullptr;
+    if (bIsCRS) {
+        formatter->setCRSExport(true);
+    }
     _exportToPROJString(formatter);
-    if (formatter->getAddNoDefs() &&
-        formatter->convention() ==
-            io::PROJStringFormatter::Convention::PROJ_4 &&
-        dynamic_cast<const crs::CRS *>(this)) {
+    if (formatter->getAddNoDefs() && bIsCRS) {
         if (!formatter->hasParam("no_defs")) {
             formatter->addParam("no_defs");
         }
     }
+    if (bIsCRS) {
+        formatter->setCRSExport(false);
+    }
     return formatter->toString();
 }
 //! @endcond
@@ -4673,6 +4677,7 @@ struct PROJStringFormatter::Private {
     bool useETMercForTMercSet_ = false;
     bool addNoDefs_ = true;
     bool coordOperationOptimizations_ = false;
+    bool crsExport_ = false;
 
     std::string result_{};
 
@@ -5311,6 +5316,14 @@ void PROJStringFormatter::ingestPROJString(
 
 // ---------------------------------------------------------------------------
 
+void PROJStringFormatter::setCRSExport(bool b) { d->crsExport_ = b; }
+
+// ---------------------------------------------------------------------------
+
+bool PROJStringFormatter::getCRSExport() const { return d->crsExport_; }
+
+// ---------------------------------------------------------------------------
+
 void PROJStringFormatter::startInversion() {
     PROJStringFormatter::Private::InversionStackElt elt;
     elt.startIter = d->steps_.end();