1 files changed, 127 insertions, 0 deletions
diff --git a/bin/reportOverlap.js b/bin/reportOverlap.js
new file mode 100755
index 0000000..902d036
--- /dev/null
+++ b/bin/reportOverlap.js
@@ -0,0 +1,127 @@
+#!/usr/bin/env node
+
+/**
+ * Report features which overlap
+ */
+
+const fs = require('fs')
+const { Readable, Transform, pipeline } = require('stream')
+const ndjson = require('ndjson')
+
+const argv = require('yargs/yargs')(process.argv.slice(2))
+  .argv
+
+if (argv._.length < 2) {
+  console.error("Usage: ./reportOverlap.js input.geojson output.geojson")
+  process.exit(1)
+}
+
+const inputFile = argv._[0]
+const outputFile = argv._[1]
+
+if (!fs.existsSync(inputFile)) {
+  console.error(`${inputFile} not found`)
+  process.exit(1)
+}
+
+let sourceCount = 0
+const features = {}
+
+/**
+ * Index features by geometry. Used as a first pass, so a second pass can easily compare
+ * features with the same geometry.
+ */
+const index = new Transform({
+  readableObjectMode: true,
+  writableObjectMode: true,
+  transform(feature, encoding, callback) {
+    sourceCount++
+
+    if (!argv.quiet) {
+      if (process.stdout.isTTY && sourceCount % 10000 === 0) {
+        process.stdout.write(` ${sourceCount.toLocaleString()}\r`)
+      }
+    }
+
+    const geometryKey = feature.geometry.coordinates.join(',')
+
+    if (!(geometryKey in features)) {
+      features[geometryKey] = []
+    }
+    features[geometryKey].push(feature)
+
+    callback()
+  }
+})
+
+let totalFeaturesWhichOverlap = 0
+let countGroupsOfOverlaps = 0
+
+/**
+ * Report features with the same geometry.
+ */
+let featureIndex = 0
+const reportOverlap = new Transform({
+  readableObjectMode: true,
+  writableObjectMode: true,
+  transform(key, encoding, callback) {
+    featureIndex++
+    if (!argv.quiet) {
+      if (process.stdout.isTTY && featureIndex % 10000 === 0) {
+        process.stdout.write(` ${featureIndex.toLocaleString()} / ${sourceCount.toLocaleString()} (${Math.round(featureIndex / sourceCount * 100)}%)\r`)
+      }
+    }
+
+    const sharedGeometry = features[key]
+
+    if (sharedGeometry.length === 1) {
+      // only one feature with this geometry
+    } else {
+      totalFeaturesWhichOverlap += sharedGeometry.length
+      countGroupsOfOverlaps++
+      this.push({
+        type: 'Feature',
+        properties: {
+          count: sharedGeometry.length
+        },
+        geometry: sharedGeometry[0].geometry
+      })
+    }
+
+    callback()
+  }
+})
+
+// first pass to index by geometry
+console.log('Pass 1/2: index by geometry')
+pipeline(
+  fs.createReadStream(inputFile),
+  ndjson.parse(),
+  index,
+  err => {
+    if (err) {
+      console.log(err)
+      process.exit(1)
+    } else {
+      console.log(`  of ${sourceCount.toLocaleString()} features found ${Object.keys(features).length.toLocaleString()} unique geometries`)
+      // second pass to report overlapping features
+      console.log('Pass 2/2: report overlapping features')
+      pipeline(
+        Readable.from(Object.keys(features)),
+        reportOverlap,
+        ndjson.stringify(),
+        fs.createWriteStream(outputFile),
+        err => {
+          if (err) {
+            console.log(err)
+            process.exit(1)
+          } else {
+            console.log(`Total overlapping features: ${totalFeaturesWhichOverlap}`)
+            console.log(`Locations with overlapping features: ${countGroupsOfOverlaps}`)
+            process.exit(0)
+          }
+        }
+      )
+    }
+  }
+)