add helper functions

nifty_gridder.cc

@@ -384,6 +384,30 @@ a_c_c to_grid (const a_d_c &uv_, const a_c_c &vis_,
   return res;
   }
 
+a_d_c to_grid_post (const a_c_c &grid_)
+  {
+  myassert(grid_.ndim()==2, "grid array must be 2D");
+  int nu = grid_.shape(0), nv = grid_.shape(1);
+  auto grid = grid_.data();
+
+  int odim[] = {nu,nv};
+  a_d_c res(odim);
+  auto grid2 = res.mutable_data();
+  for (int u=0; u<nu; ++u)
+    {
+    int xu = (u==0) ? 0 : nu-u;
+    for (int v=0; v<nv; ++v)
+      {
+      int xv = (v==0) ? 0 : nv-v;
+      int i1 = u*nv+v;
+      int i2 = xu*nv+xv;
+      grid2[i1] = 0.5*(grid[i1].real()+grid[i1].imag()+
+                       grid[i2].real()-grid[i2].imag());
+      }
+    }
+  return res;
+  }
+
 a_c_c from_grid (const a_d_c &uv_, const a_c_c &grid_,
   int nu, int nv, int nspread, double r2lamb)
   {
@@ -425,6 +449,31 @@ a_c_c from_grid (const a_d_c &uv_, const a_c_c &grid_,
   return res;
   }
 
+a_c_c from_grid_pre (const a_d_c &grid_)
+  {
+  myassert(grid_.ndim()==2, "grid array must be 2D");
+  int nu = grid_.shape(0), nv = grid_.shape(1);
+  auto grid = grid_.data();
+
+  int odim[] = {nu,nv};
+  a_c_c res(odim);
+  auto grid2 = res.mutable_data();
+  for (int u=0; u<nu; ++u)
+    {
+    int xu = (u==0) ? 0 : nu-u;
+    for (int v=0; v<nv; ++v)
+      {
+      int xv = (v==0) ? 0 : nv-v;
+      int i1 = u*nv+v;
+      int i2 = xu*nv+xv;
+      double v1 = 0.5*grid[i1];
+      double v2 = 0.5*grid[i2];
+      grid2[i1] = complex<double>(v1+v2, v1-v2);
+      }
+    }
+  return res;
+  }
+
 } // unnamed namespace
 
 PYBIND11_MODULE(nifty_gridder, m)
@@ -433,5 +482,7 @@ PYBIND11_MODULE(nifty_gridder, m)
 
   m.def("peanoindex",&peanoindex);
   m.def("to_grid",&to_grid);
+  m.def("to_grid_post",&to_grid_post);
   m.def("from_grid",&from_grid);
+  m.def("from_grid_pre",&from_grid_pre);
   }