CFSimpleIndexer.md

@@ -100,7 +100,7 @@ We next must define mappings from indexes in the space defined by `subset_indexe
   unsigned mueller_map[]{0, 5, 10, 15};
 ```
 
-Finally we define the CF values through a `CFArray` sub-class instance with the appropriate element indexing operator (taking some liberties with C++ and CASA syntax):
+We next define the CF values through a `CFArray` sub-class instance with the appropriate element indexing operator (taking some liberties with C++ and CASA syntax):
 ```c++
 class MyCFArray : public hpg::CFArray {
   unsigned m_w_map[1];
@@ -117,7 +117,7 @@ class MyCFArray : public hpg::CFArray {
   operator()(unsigned x, unsigned y, unsigned mueller, unsigned cube, unsigned group)
     const override {
 
-    hpg::CellIndex ci = m_subset_indexer({mueller, cube, group});
+    hpg::CellIndex ci = m_subset_indexer.cell_index({mueller, cube, group});
     assert(ci.m_w_plane == 0);
     assert(ci.m_mueller < 4);
     return m_store(ci.m_baseline_class, ci.m_time, m_w_map[ci.m_w_plane], ci.m_frequency, m_mueller_map[ci.m_mueller], x, y);
@@ -126,3 +126,17 @@ class MyCFArray : public hpg::CFArray {
   //...
 };
 ```
+
+Finally, the values of `hpg::VisData<N>::m_cf_index` may be computed as in the following
+```c++
+  hpg::VisData<N> vis;
+  hpg::CellIndex cell_index;
+  // initialize fields of cell_index using visibility metadata
+  cell_index.m_baseline_type = 0;
+  cell_index.m_time = /*... from visibility time */;
+  cell_index.m_w_plane = W_0;
+  cell_index.m_frequency = /*... from visibility frequency */
+  cell_index.m_mueller = 0; // not significant, 0 is always valid
+  auto [mueller, cube, group] = subset_indexer.cf_index(cell_index);
+  vis.m_cf_index = {cube, group};
+```
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