PROJStringFormatter::toString(): optimize hgridshift, vgridshift, hgridshift inv constructs

Given an initial pipeline with

+step +proj=hgridshift +grids=foo
+step +proj=vgridshift +grids=bar
+step +inv +proj=hgridshift +grids=foo

Transform it as

+step +proj=push +v_1 +v_2
+step +proj=hgridshift +grids=foo +omit_inv
+step +proj=vgridshift +grids=bar
+step +inv +proj=hgridshift +grids=foo +omit_fwd
+step +proj=pop +v_1 +v_2

So as to avoid doing a double application of the hgridshift.

2 files changed, 133 insertions, 0 deletions

diff --git a/src/iso19111/io.cpp b/src/iso19111/io.cpp
index d994277b..0d98e2de 100644
--- a/src/iso19111/io.cpp
+++ b/src/iso19111/io.cpp
@@ -6278,6 +6278,10 @@ struct Step {
             return key == otherKey && value == otherVal;
         }
 
+        bool operator==(const KeyValue &other) const noexcept {
+            return key == other.key && value == other.value;
+        }
+
         bool operator!=(const KeyValue &other) const noexcept {
             return key != other.key || value != other.value;
         }
@@ -6799,6 +6803,46 @@ const std::string &PROJStringFormatter::toString() const {
                 }
             }
 
+            // +step +proj=hgridshift +grids=grid_A
+            // +step +proj=vgridshift [...] <== curStep
+            // +step +inv +proj=hgridshift +grids=grid_A
+            // ==>
+            // +step +proj=push +v_1 +v_2
+            // +step +proj=hgridshift +grids=grid_A +omit_inv
+            // +step +proj=vgridshift [...]
+            // +step +inv +proj=hgridshift +grids=grid_A +omit_fwd
+            // +step +proj=pop +v_1 +v_2
+            if (i + 1 < d->steps_.size() && prevStep.name == "hgridshift" &&
+                prevStepParamCount == 1 && curStep.name == "vgridshift") {
+                auto iterNext = iterCur;
+                ++iterNext;
+                auto &nextStep = *iterNext;
+                if (nextStep.name == "hgridshift" &&
+                    nextStep.inverted != prevStep.inverted &&
+                    nextStep.paramValues.size() == 1 &&
+                    prevStep.paramValues[0] == nextStep.paramValues[0]) {
+                    Step pushStep;
+                    pushStep.name = "push";
+                    pushStep.paramValues.emplace_back("v_1");
+                    pushStep.paramValues.emplace_back("v_2");
+                    d->steps_.insert(iterPrev, pushStep);
+
+                    prevStep.paramValues.emplace_back("omit_inv");
+
+                    nextStep.paramValues.emplace_back("omit_fwd");
+
+                    Step popStep;
+                    popStep.name = "pop";
+                    popStep.paramValues.emplace_back("v_1");
+                    popStep.paramValues.emplace_back("v_2");
+                    ++iterNext;
+                    d->steps_.insert(iterNext, popStep);
+
+                    changeDone = true;
+                    break;
+                }
+            }
+
             // detect a step and its inverse
             if (curStep.inverted != prevStep.inverted &&
                 curStep.name == prevStep.name &&
diff --git a/test/unit/test_io.cpp b/test/unit/test_io.cpp
index 07c4c6f1..0dc0dc1c 100644
--- a/test/unit/test_io.cpp
+++ b/test/unit/test_io.cpp
@@ -6832,6 +6832,95 @@ TEST(io, projstringformatter_axisswap_unitconvert_axisswap) {
 
 // ---------------------------------------------------------------------------
 
+TEST(io, projstringformatter_optim_hgridshift_vgridshift_hgridshift_inv) {
+    // Nominal case
+    {
+        auto fmt = PROJStringFormatter::create();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+
+        fmt->addStep("vgridshift");
+        fmt->addParam("grids", "bar");
+
+        fmt->startInversion();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+        fmt->stopInversion();
+
+        EXPECT_EQ(fmt->toString(),
+                  "+proj=pipeline "
+                  "+step +proj=push +v_1 +v_2 "
+                  "+step +proj=hgridshift +grids=foo +omit_inv "
+                  "+step +proj=vgridshift +grids=bar "
+                  "+step +inv +proj=hgridshift +grids=foo +omit_fwd "
+                  "+step +proj=pop +v_1 +v_2");
+    }
+
+    // Variant with first hgridshift inverted, and second forward
+    {
+        auto fmt = PROJStringFormatter::create();
+
+        fmt->startInversion();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+        fmt->stopInversion();
+
+        fmt->addStep("vgridshift");
+        fmt->addParam("grids", "bar");
+
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+
+        EXPECT_EQ(fmt->toString(),
+                  "+proj=pipeline "
+                  "+step +proj=push +v_1 +v_2 "
+                  "+step +inv +proj=hgridshift +grids=foo +omit_inv "
+                  "+step +proj=vgridshift +grids=bar "
+                  "+step +proj=hgridshift +grids=foo +omit_fwd "
+                  "+step +proj=pop +v_1 +v_2");
+    }
+
+    // Do not apply ! not same grid name
+    {
+        auto fmt = PROJStringFormatter::create();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+
+        fmt->addStep("vgridshift");
+        fmt->addParam("grids", "bar");
+
+        fmt->startInversion();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo2");
+        fmt->stopInversion();
+
+        EXPECT_EQ(fmt->toString(), "+proj=pipeline "
+                                   "+step +proj=hgridshift +grids=foo "
+                                   "+step +proj=vgridshift +grids=bar "
+                                   "+step +inv +proj=hgridshift +grids=foo2");
+    }
+
+    // Do not apply ! missing inversion
+    {
+        auto fmt = PROJStringFormatter::create();
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+
+        fmt->addStep("vgridshift");
+        fmt->addParam("grids", "bar");
+
+        fmt->addStep("hgridshift");
+        fmt->addParam("grids", "foo");
+
+        EXPECT_EQ(fmt->toString(), "+proj=pipeline "
+                                   "+step +proj=hgridshift +grids=foo "
+                                   "+step +proj=vgridshift +grids=bar "
+                                   "+step +proj=hgridshift +grids=foo");
+    }
+}
+
+// ---------------------------------------------------------------------------
+
 TEST(io, projparse_longlat) {
 
     auto expected = "GEODCRS[\"unknown\",\n"