From 5039b0dbf3af3b93466069927d794f5b1c8ccf81 Mon Sep 17 00:00:00 2001
From: Andrew Harvey <andrew@alantgeo.com.au>
Date: Tue, 4 May 2021 14:50:52 +1000
Subject: add cluster library

---
 cluster.js | 64 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 64 insertions(+)
 create mode 100644 cluster.js

(limited to 'cluster.js')

diff --git a/cluster.js b/cluster.js
new file mode 100644
index 0000000..c716063
--- /dev/null
+++ b/cluster.js
@@ -0,0 +1,64 @@
+const CheapRuler = require('cheap-ruler')
+const ruler = new CheapRuler(-37, 'meters')
+
+/**
+ * Cluster points together where within threshold distance.
+ *
+ * @param {Array} features - GeoJSON Point Features
+ * @param {number} thresholdDistance - Maximum distance between points to cluster together
+ *
+ * @returns {Array} clusters, where unclustered features are returned as single feature clusters
+ */
+module.exports = (features, thresholdDistance) => {
+  // Array of clusters where each cluster is a Set of feature index's
+  const clusters = []
+
+  features.map((a, ai) => {
+    features.map((b, bi) => {
+      // skip comparing with self
+      if (ai === bi) return
+
+      const distance = ruler.distance(a.geometry.coordinates, b.geometry.coordinates)                                                        
+      if (distance < thresholdDistance) {
+        // link into a cluster
+        let addedToExistingCluster = false
+        clusters.forEach((cluster, i) => {
+          if (cluster.has(ai) || cluster.has(bi)) {
+            // insert into this cluster
+            clusters[i].add(ai)
+            clusters[i].add(bi)
+
+            addedToExistingCluster = true
+          }
+        })
+
+        if (!addedToExistingCluster) {
+          // create a new cluster
+          const newCluster = new Set()
+          newCluster.add(ai)
+          newCluster.add(bi)
+          clusters.push(newCluster)
+        }
+      } // else don't cluster together
+    })
+  })
+
+  // result is array of clusters, including non-clustered features as single item clusters
+  const result = clusters.map(cluster => {
+    return Array.from(cluster).map(index => {
+      return features[index]
+    })
+  })
+
+  // find features not clustered
+  features.map((feature, index) => {
+    // if feature not a cluster, return as an single item cluster
+    const featureInACluster = clusters.map(cluster => cluster.has(index)).reduce((acc, cur) => acc || !!cur, false)
+    if (!featureInACluster) {
+      result.push([feature])
+    }
+  })
+
+  return result
+
+}
-- 
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