Pipeline: support +omit_fwd and +omit_inv keywords

Inspired from syntax of https://github.com/OSGeo/PROJ/pull/453/files
but 'rebased' on top of previous commit that cleans up the pipeline implementation

Different situations:
- +omit_fwd:
    the step when followed in the forward path will be omitted
    the step when followed in the reverse path will be executed
- +omit_fwd +inv:
    the step when followed in the forward path will be omitted
    the step when followed in the reverse path will be executed (with the inv method)
- +omit_inv:
    the step when followed in the forward path will be executed
    the step when followed in the reverse path will be omitted
- +omit_inv +inv:
    the step when followed in the forward path will be executed (with the inv method)
    the step when followed in the reverse path will be omitted

This will be used in the next commit to optimize constructs like

+step +proj=hgridshift +grids=foo
+step +proj=vgridshift +grids=bar
+step +inv +proj=hgridshift +grids=foo

Such steps are used for CRS to CRS transformations where applying the vertical grid
requires to do a transformation to an interpolating CRS. One can notice that
in the last step will just restore the horizontal coordinates before the first step, so
doing an inverse hgridshift is overkill.

So that could be optimized as:

+step +proj=push +v_1 +v_2
+step +proj=hgridshift +grids=foo +omit_inv
+step +proj=vgridshift +grids=bar
+step +inv +proj=hgridshift +grids=foo +omit_fwd
+step +proj=pop +v_1 +v_2

In the forward path, this will be equivalent to:
+step +proj=push +v_1 +v_2
+step +proj=hgridshift +grids=foo
+step +proj=vgridshift +grids=bar
+step +prop=pop +v_1 +v_2

And similarly in the reverse path, this will be quivalent to:
+step +proj=push +v_1 +v_2
+step +proj=hgridshift +grids=foo
+step +inv +proj=vgridshift +grids=bar
+step +proj=pop +v_1 +v_2

1 files changed, 49 insertions, 0 deletions

diff --git a/test/gie/4D-API_cs2cs-style.gie b/test/gie/4D-API_cs2cs-style.gie
index 19b3ad96..e5722b5e 100644
--- a/test/gie/4D-API_cs2cs-style.gie
+++ b/test/gie/4D-API_cs2cs-style.gie
@@ -386,6 +386,55 @@ operation   +proj=pop +v_3
 accept      12 56 0 0
 expect      12 56 0 0
 
+-------------------------------------------------------------------------------
+Test Pipeline +omit_inv
+-------------------------------------------------------------------------------
+
+operation   +proj=pipeline
+                +step +proj=affine +xoff=1 +yoff=1 +omit_inv
+
+accept      2 49 0 0
+expect      3 50 0 0
+
+direction inverse
+accept      2 49 0 0
+expect      2 49 0 0
+
+
+operation   +proj=pipeline
+                +step +inv +proj=affine +xoff=1 +yoff=1 +omit_inv
+
+accept      2 49 0 0
+expect      1 48 0 0
+
+direction inverse
+accept      2 49 0 0
+expect      2 49 0 0
+
+-------------------------------------------------------------------------------
+Test Pipeline +omit_fwd
+-------------------------------------------------------------------------------
+
+operation   +proj=pipeline
+                +step +proj=affine +xoff=1 +yoff=1 +omit_fwd
+
+accept      2 49 0 0
+expect      2 49 0 0
+
+direction inverse
+accept      2 49 0 0
+expect      1 48 0 0
+
+
+operation   +proj=pipeline
+                +step +inv +proj=affine +xoff=1 +yoff=1 +omit_fwd
+
+accept      2 49 0 0
+expect      2 49 0 0
+
+direction inverse
+accept      2 49 0 0
+expect      3 50 0 0
 
 -------------------------------------------------------------------------------
 Test bugfix of https://github.com/OSGeo/proj.4/issues/1002