Add fallback_strategy to tinshift transform

 - this bumps format_version of tinshift JSON to 1.1 for the new field
   fallback_strategy
 - the default behaviour without that field is retained
 - if fallback_strategy is set to "nearest_side", then points that do not fall
   into any of the triangles will be transformed according to the nearest
   triangle
 - if fallback_centroid is set to "nearest_side", then points that do not fall
   into any of the triangles will be transformed according to the triangle
   with the nearest centroid

2 files changed, 79 insertions, 0 deletions

diff --git a/test/gie/tinshift.gie b/test/gie/tinshift.gie
index f16c16bb..85009537 100644
--- a/test/gie/tinshift.gie
+++ b/test/gie/tinshift.gie
@@ -47,4 +47,16 @@ accept      3210000.0000 6700000.0000   10.0
 expect      3210000.0000 6700000.0000   10.2886
 roundtrip   1
 
+# Test fallback strategy nearest_side
+operation   +proj=tinshift +file=tests/tinshift_fallback_nearest_side.json
+accept    2    3
+expect    4    6
+roundtrip 1
+
+# Test fallback strategy nearest_centroid
+operation   +proj=tinshift +file=tests/tinshift_fallback_nearest_centroid.json
+accept    3    0
+expect    3    0
+roundtrip 1
+
 </gie-strict>
diff --git a/test/unit/test_tinshift.cpp b/test/unit/test_tinshift.cpp
index 96da6e25..2b42294f 100644
--- a/test/unit/test_tinshift.cpp
+++ b/test/unit/test_tinshift.cpp
@@ -65,6 +65,7 @@ TEST(tinshift, basic) {
         EXPECT_EQ(f->formatVersion(), "1.0");
         EXPECT_EQ(f->inputCRS(), "EPSG:2393");
         EXPECT_EQ(f->outputCRS(), "EPSG:3067");
+        EXPECT_EQ(f->fallbackStrategy(), FALLBACK_NONE);
 
         auto eval = Evaluator(std::move(f));
         double x_out = 0;
@@ -206,6 +207,72 @@ TEST(tinshift, basic) {
         EXPECT_EQ(y_out, 0.75);
         EXPECT_EQ(z_out, 1000.0);
     }
+
+    // invalid fallback_strategy field with 1.0 version
+    {
+        auto j(jMinValid);
+        j["fallback_strategy"] = "none";
+        EXPECT_THROW(TINShiftFile::parse(j.dump()), ParsingException);
+    }
+
+    // invalid fallback_strategy field with 1.1 version
+    {
+        auto j(jMinValid);
+        j["format_version"] = "1.1";
+        j["fallback_strategy"] = "invalid";
+        EXPECT_THROW(TINShiftFile::parse(j.dump()), ParsingException);
+    }
+
+    // fail with no triangles and fallback nearest_side
+    {
+        auto j(jMinValid);
+        j["format_version"] = "1.1";
+        j["fallback_strategy"] = "nearest_side";
+        j["triangles"] = json::array(); // empty
+
+        auto f = TINShiftFile::parse(j.dump());
+        auto eval = Evaluator(std::move(f));
+        double x_out = 0;
+        double y_out = 0;
+        double z_out = 0;
+
+        EXPECT_FALSE(eval.forward(1.0, 1.0, 1.0, x_out, y_out, z_out));
+    }
+
+    // fail with only degenerate triangles (one size is zero length) and
+    // fallback nearest_side
+    {
+        auto j(jMinValid);
+        j["format_version"] = "1.1";
+        j["fallback_strategy"] = "nearest_side";
+        j["vertices"] = {{0, 0, 101, 101}, {0, 1, 100, 101}, {0, 1, 100, 100}};
+
+        auto f = TINShiftFile::parse(j.dump());
+        auto eval = Evaluator(std::move(f));
+        double x_out = 0;
+        double y_out = 0;
+        double z_out = 0;
+
+        EXPECT_FALSE(eval.forward(1.0, 1.0, 1.0, x_out, y_out, z_out));
+    }
+
+    // fail with only degenerate triangles (two angles are 0°) and fallback
+    // nearest_side
+    {
+        auto j(jMinValid);
+        j["format_version"] = "1.1";
+        j["fallback_strategy"] = "nearest_side";
+        j["vertices"] = {
+            {0, 0, 101, 101}, {0, 0.5, 100, 101}, {0, 1, 100, 100}};
+
+        auto f = TINShiftFile::parse(j.dump());
+        auto eval = Evaluator(std::move(f));
+        double x_out = 0;
+        double y_out = 0;
+        double z_out = 0;
+
+        EXPECT_FALSE(eval.forward(1.0, 1.0, 1.0, x_out, y_out, z_out));
+    }
 }
 
 } // namespace