Add pipeline for finding station by distance

Signed-off-by: Fred Boniface <fred@fjla.uk>

src/utils/ldbPipeline.utils.ts

@@ -0,0 +1,42 @@
+export function findStationsByDistancePipeline(count: number) {
+  return [
+    {
+      '$geoNear': {
+        'near': {
+          'type': 'Point', 
+          'coordinates': [
+            -5.149929, 58.350661
+          ]
+        }, 
+        'distanceField': 'distance'
+      }
+    }, {
+      '$limit': count
+    }, {
+      '$addFields': {
+        'miles': {
+          '$divide': [
+            {
+              '$round': {
+                '$multiply': [
+                  {
+                    '$divide': [
+                      '$distance', 1609.34
+                    ]
+                  }, 4
+                ]
+              }
+            }, 4
+          ]
+        }
+      }
+    }, {
+      '$project': {
+        '_id': 0, 
+        '3ALPHA': 1, 
+        'NLCDESC': 1, 
+        'miles': 1
+      }
+    }
+  ]
+}