FEAT: start to ion->neu grid matchup

Author: aaronjridley

src/grid_match.cpp

@@ -0,0 +1,46 @@
+// Copyright 2025, the Aether Development Team (see doc/dev_team.md for members)
+// Full license can be found in License.md
+
+#include "aether.h"
+
+bool grid_match(Grid gGrid, 
+                Grid mGrid, 
+                Quadtree gQuadtree,
+                Quadtree mQuadtree) {
+
+  // Let's do magnetic to geographic first:
+
+  int64_t iX, mnX = mGrid.get_nX();
+  int64_t iY, mnY = mGrid.get_nY();
+  int64_t iZ, mnZ = mGrid.get_nZ();
+  int64_t mGCs = mGrid.get_nGCs();
+  precision_t lon, lat;
+  precision_t normX, normY, normZ;
+  arma_vec norms(3);
+  int64_t iNode;
+
+  for (iX = mGCs; iX < mnX - mGCs; iX++) {
+    for (iY = mGCs; iY < mnY - mGCs; iY++) {
+      for (iZ = mGCs; iZ < mnZ - mGCs; iZ++) {
+        lon = mGrid.geoLon_scgc(iX, iY, iZ);
+        lat = mGrid.geoLat_scgc(iX, iY, iZ);
+        if (gGrid.iGridShape_ == gGrid.iSphere_) {
+          norms(0) = lon / cPI;
+          norms(1) = lat / cPI;
+          norms(2) = 0.0;
+          iNode = gQuadtree.find_point(norms);
+        } else {
+          norms = sphere_to_cube(lon, lat);
+          iNode = gQuadtree.find_point(norms);
+        }
+        std::cout << "lon, lat, node: " << lon*cRtoD << " "
+        << lat*cRtoD << " "
+        << norms(0) << " "
+        << norms(1) << " "
+        << norms(2) << " "
+        << iNode << "\n";
+      }
+    }
+  }
+  return true;
+}