FEAT: start to ion->neu grid matchup

Author: aaronjridley

include/calc_grid_derived.h

@@ -16,4 +16,12 @@ arma_vec calc_bin_edges(arma_vec centers);
 std::vector<precision_t> calc_bin_widths(std::vector<precision_t> centers);
 arma_vec calc_bin_widths(arma_vec centers);
 
+// ----------------------------------------------------------------------------
+// A helper function for mapping grids
+// ----------------------------------------------------------------------------
+bool grid_match(Grid gGrid, 
+                Grid mGrid, 
+                Quadtree gQuadtree,
+                Quadtree mQuadtree);
+
 #endif  // INCLUDE_CALC_GRID_DERIVED_H_