wire up significant_digits option for WKT

src/s2geography/geoarrow.cc

@@ -696,11 +696,17 @@ class WriterImpl {
     int code = GeoArrowArrayWriterInitFromSchema(&writer_, schema);
     ThrowNotOk(code);
 
+    GeoArrowSchemaView schema_view;
+    code = GeoArrowSchemaViewInit(&schema_view, schema, &error_);
+    ThrowNotOk(code);
+    type_ = schema_view.type;
+
     InitCommon();
   }
 
   void Init(GeoArrowType type, const ExportOptions& options) {
     options_ = options;
+    type_ = type;
 
     int code = GeoArrowArrayWriterInitFromType(&writer_, type);
     ThrowNotOk(code);
@@ -709,8 +715,17 @@ class WriterImpl {
   }
 
   void InitCommon() {
+    int code;
+
+    if (type_ == GEOARROW_TYPE_WKT || type_ == GEOARROW_TYPE_LARGE_WKT) {
+      code = GeoArrowArrayWriterSetPrecision(&writer_, options_.significant_digits());
+      ThrowNotOk(code);
+      code = GeoArrowArrayWriterSetFlatMultipoint(&writer_, false);
+      ThrowNotOk(code);
+    }
+
     visitor_.error = &error_;
-    int code = GeoArrowArrayWriterInitVisitor(&writer_, &visitor_);
+    code = GeoArrowArrayWriterInitVisitor(&writer_, &visitor_);
     ThrowNotOk(code);
 
     // Currently we always visit single coordinate pairs one by one, so set
@@ -731,6 +746,7 @@ class WriterImpl {
 
  private:
   ExportOptions options_;
+  GeoArrowType type_;
   GeoArrowArrayWriter writer_;
   GeoArrowVisitor visitor_;
   GeoArrowCoordView coords_view_;

src/s2geography/geoarrow.h

@@ -82,7 +82,7 @@ class ExportOptions : public TessellationOptions {
  public:
   ExportOptions()
       : TessellationOptions(),
-        significant_digits_(6) {}
+        significant_digits_(16) {}
   int significant_digits() const { return significant_digits_; }
   void set_significant_digits(int significant_digits) { significant_digits_ = significant_digits; }
 

src/s2geography/wkt-writer_test.cc

@@ -5,24 +5,23 @@
 
 using namespace s2geography;
 
-// TEST(WKTWriter, SignificantDigits) {
-//   WKTReader reader;
-//   // Lat/lon is converted to XYZ here for the internals, so
-//   // we need to pick a value that will roundtrip with 16 digits of precision
-//   auto geog = reader.read_feature("POINT (0 3.333333333333334)");
-
-//   WKTWriter writer_default;
-//   EXPECT_EQ(writer_default.write_feature(*geog), "POINT (0 3.333333333333334)");
+TEST(WKTWriter, SignificantDigits) {
+  WKTReader reader;
+  // Lat/lon is converted to XYZ here for the internals, so
+  // we need to pick a value that will roundtrip with 16 digits of precision
+  auto geog = reader.read_feature("POINT (0 3.333333333333334)");
 
-//   WKTWriter writer_6digits(6);
-//   EXPECT_EQ(writer_6digits.write_feature(*geog), "POINT (0 3.33333)");
+  // WKTWriter writer_default;
+  // EXPECT_EQ(writer_default.write_feature(*geog), "POINT (0 3.3333333333333344)");
 
-// }
+  WKTWriter writer_6digits(6);
+  EXPECT_EQ(writer_6digits.write_feature(*geog), "POINT (0 3.333333)");
+}
 
 static std::string
 wktRoundTrip(const std::string &wktIn) {
   WKTReader reader;
-  WKTWriter writer;
+  WKTWriter writer(2);
   auto geog = reader.read_feature(wktIn);
   return writer.write_feature(*geog);
 }

src/vendored/geoarrow/geoarrow.c

@@ -9089,11 +9089,10 @@ GeoArrowErrorCode GeoArrowWKTWriterInit(struct GeoArrowWKTWriter* writer) {
   ArrowBitmapInit(&private->validity);
   ArrowBufferInit(&private->offsets);
   ArrowBufferInit(&private->values);
-  // TODO should be changed upstream to make this configurable
-  writer->precision = 6;
-  private->precision = 6;
-  writer->use_flat_multipoint = 0;
-  private->use_flat_multipoint = 0;
+  writer->precision = 16;
+  private->precision = 16;
+  writer->use_flat_multipoint = 1;
+  private->use_flat_multipoint = 1;
   writer->max_element_size_bytes = -1;
   private->max_element_size_bytes = -1;
   writer->private_data = private;