Make tmerc an alias for etmerc. (#1234)

* Make tmerc an alias for etmerc

This switches the algorithm used in tmerc to the Poder/Engsager
tmerc algorithm. The original tmerc algorithm of Evenden/Snyder
origin can still be accessed by adding the +approx flag when
initializing a tmerc projection. The +approx flag can also
be used when initializing UTM projections, in which case the
Evenden/Snyder algorithm is used as well.

If a tmerc projection is instantiated on a spherical earth
the Evenden/Snyder algorithm is used as well since the
Poder/Engsager algorithm is only defined on the ellipsoid.

+proj=etmerc can still be instantiated for backwards compatibility
reasons.

Co-authored-by: Kristian Evers <kristianevers@gmail.com>
Co-authored-by: Even Rouault <even.rouault@spatialys.com>

1 files changed, 8 insertions, 8 deletions

diff --git a/test/unit/test_operation.cpp b/test/unit/test_operation.cpp
index 6c1ecf1c..586226e2 100644
--- a/test/unit/test_operation.cpp
+++ b/test/unit/test_operation.cpp
@@ -1237,9 +1237,9 @@ TEST(operation, tmerc_export) {
 
     {
         auto formatter = PROJStringFormatter::create();
-        formatter->setUseETMercForTMerc(true);
+        formatter->setUseApproxTMerc(true);
         EXPECT_EQ(conv->exportToPROJString(formatter.get()),
-                  "+proj=etmerc +lat_0=1 +lon_0=2 +k=3 +x_0=4 +y_0=5");
+                  "+proj=tmerc +approx +lat_0=1 +lon_0=2 +k=3 +x_0=4 +y_0=5");
     }
 
     EXPECT_EQ(conv->exportToWKT(WKTFormatter::create().get()),
@@ -6061,21 +6061,21 @@ TEST(operation, compoundCRS_to_compoundCRS_with_vertical_transform) {
               "+ellps=WGS84");
     {
         auto formatter = PROJStringFormatter::create();
-        formatter->setUseETMercForTMerc(true);
+        formatter->setUseApproxTMerc(true);
         EXPECT_EQ(op->exportToPROJString(formatter.get()),
-                  "+proj=pipeline +step +inv +proj=etmerc +lat_0=1 +lon_0=2 "
+                  "+proj=pipeline +step +inv +proj=tmerc +approx +lat_0=1 +lon_0=2 "
                   "+k=3 +x_0=4 +y_0=5 +ellps=WGS84 +step "
                   "+proj=vgridshift +grids=bla.gtx +multiplier=0.001 +step "
-                  "+proj=utm +zone=32 "
+                  "+proj=utm +approx +zone=32 "
                   "+ellps=WGS84");
     }
     {
         auto formatter = PROJStringFormatter::create();
-        formatter->setUseETMercForTMerc(true);
+        formatter->setUseApproxTMerc(true);
         EXPECT_EQ(op->inverse()->exportToPROJString(formatter.get()),
-                  "+proj=pipeline +step +inv +proj=utm +zone=32 +ellps=WGS84 "
+                  "+proj=pipeline +step +inv +proj=utm +approx +zone=32 +ellps=WGS84 "
                   "+step +inv +proj=vgridshift +grids=bla.gtx "
-                  "+multiplier=0.001 +step +proj=etmerc +lat_0=1 +lon_0=2 "
+                  "+multiplier=0.001 +step +proj=tmerc +approx +lat_0=1 +lon_0=2 "
                   "+k=3 +x_0=4 +y_0=5 +ellps=WGS84");
     }