createUnitOfMeasure(): use full double resolution for the conversion factor (#2011)

Fixes https://github.com/OSGeo/gdal/issues/2290 where it was found that
PROJ returned value for conversion factor of US Survey Foot unit wasn't
at the maximum resolution, but only accurate to 15 significant digits.

1 files changed, 8 insertions, 0 deletions

diff --git a/test/unit/test_factory.cpp b/test/unit/test_factory.cpp
index 4f6f2c93..c7ae458e 100644
--- a/test/unit/test_factory.cpp
+++ b/test/unit/test_factory.cpp
@@ -95,6 +95,14 @@ TEST(factory, AuthorityFactory_createUnitOfMeasure_linear) {
 
 // ---------------------------------------------------------------------------
 
+TEST(factory, AuthorityFactory_createUnitOfMeasure_linear_us_survey_foot) {
+    auto factory = AuthorityFactory::create(DatabaseContext::create(), "EPSG");
+    auto uom = factory->createUnitOfMeasure("9003");
+    EXPECT_EQ(uom->conversionToSI(), 12. / 39.37);
+}
+
+// ---------------------------------------------------------------------------
+
 TEST(factory, AuthorityFactory_createUnitOfMeasure_angular) {
     auto factory = AuthorityFactory::create(DatabaseContext::create(), "EPSG");
     auto uom = factory->createUnitOfMeasure("9102");