Add no-op operation. It does nothing.

7 files changed, 68 insertions, 0 deletions

diff --git a/docs/source/operations/conversions/index.rst b/docs/source/operations/conversions/index.rst
index a9d137ab..42ad079d 100644
--- a/docs/source/operations/conversions/index.rst
+++ b/docs/source/operations/conversions/index.rst
@@ -15,6 +15,7 @@ conversions.
    cart
    geoc
    latlon
+   noop
    pop
    push
    unitconvert
diff --git a/docs/source/operations/conversions/noop.rst b/docs/source/operations/conversions/noop.rst
new file mode 100644
index 00000000..a35b2b58
--- /dev/null
+++ b/docs/source/operations/conversions/noop.rst
@@ -0,0 +1,28 @@
+.. _noop:
+
+================================================================================
+No operation
+================================================================================
+
+.. versionadded:: 6.1.0
+
+Pass a coordinate through unchanged.
+
++---------------------+--------------------------------------------------------+
+| **Alias**           | noop                                                   |
++---------------------+--------------------------------------------------------+
+| **Domain**          | 4D                                                     |
++---------------------+--------------------------------------------------------+
+| **Input type**      | Any                                                    |
++---------------------+--------------------------------------------------------+
+| **Output type**     | Any                                                    |
++---------------------+--------------------------------------------------------+
+
+The no operation is a dummy operation that returns whatever is passed to it
+as seen in this example::
+
+    $ echo 12 34 56 78 | cct +proj=noop
+      12.0000        34.0000       56.0000       78.0000
+
+The operation has no options and default options will not affect the output.
+
diff --git a/src/Makefile.am b/src/Makefile.am
index b62a11b0..9858d78f 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -173,6 +173,7 @@ libproj_la_SOURCES = \
 	conversions/cart.cpp \
 	conversions/geoc.cpp \
 	conversions/geocent.cpp \
+	conversions/noop.cpp \
 	conversions/unitconvert.cpp \
 	\
 	transformations/affine.cpp \
diff --git a/src/conversions/noop.cpp b/src/conversions/noop.cpp
new file mode 100644
index 00000000..a5dd6023
--- /dev/null
+++ b/src/conversions/noop.cpp
@@ -0,0 +1,19 @@
+#define PJ_LIB__
+
+#include "proj_internal.h"
+
+PROJ_HEAD(noop,    "No operation");
+
+static PJ_COORD noop(PJ_COORD coord, PJ *P) {
+    (void) P;
+    return coord;
+}
+
+PJ *CONVERSION(noop, 0) {
+    P->fwd4d = noop;
+    P->inv4d = noop;
+    P->left  = PJ_IO_UNITS_WHATEVER;
+    P->right = PJ_IO_UNITS_WHATEVER;
+    return P;
+}
+
diff --git a/src/lib_proj.cmake b/src/lib_proj.cmake
index 72a8cc59..38bc05d8 100644
--- a/src/lib_proj.cmake
+++ b/src/lib_proj.cmake
@@ -174,6 +174,7 @@ set(SRC_LIBPROJ_CONVERSIONS
   conversions/cart.cpp
   conversions/geoc.cpp
   conversions/geocent.cpp
+  conversions/noop.cpp
   conversions/unitconvert.cpp
 )
 
diff --git a/src/pj_list.h b/src/pj_list.h
index 8ab4cdc0..0923bba8 100644
--- a/src/pj_list.h
+++ b/src/pj_list.h
@@ -106,6 +106,7 @@ PROJ_HEAD(nell_h, "Nell-Hammer")
 PROJ_HEAD(nicol, "Nicolosi Globular")
 PROJ_HEAD(nsper, "Near-sided perspective")
 PROJ_HEAD(nzmg, "New Zealand Map Grid")
+PROJ_HEAD(noop, "No operation")
 PROJ_HEAD(ob_tran, "General Oblique Transformation")
 PROJ_HEAD(ocea, "Oblique Cylindrical Equal Area")
 PROJ_HEAD(oea, "Oblated Equal Area")
diff --git a/test/gie/more_builtins.gie b/test/gie/more_builtins.gie
index e16443d4..f6b52ea3 100644
--- a/test/gie/more_builtins.gie
+++ b/test/gie/more_builtins.gie
@@ -756,4 +756,21 @@ expect    359 10 0
 
 -------------------------------------------------------------------------------
 
+-------------------------------------------------------------------------------
+# No-op
+-------------------------------------------------------------------------------
+operation +proj=noop
+direction forward
+accept  25  25
+expect  25  25
+
+accept  25  25  25
+expect  25  25  25
+
+accept  25  25  25  25
+expect  25  25  25  25
+-------------------------------------------------------------------------------
+
+
+
 </gie>