Change mapping from zoom levels to geohash precision

src/ui/public/agg_types/__tests__/buckets/_geo_hash.js

@@ -0,0 +1,60 @@
+import expect from 'expect.js';
+import AggTypesBucketsGeoHashProvider from 'ui/agg_types/buckets/geo_hash';
+
+describe('Geohash Agg', function () {
+
+
+  describe('write', function () {
+
+    let paramWriter = new AggTypesBucketsGeoHashProvider(function PrivateMock() {
+      return function BucketMock(geohashProvider) {
+        return geohashProvider.params[4];
+      };
+    }, {});
+
+    describe('interval', function () {
+
+      const zoomToGeoHashPrecision = {
+        0: 1,
+        1: 2,
+        2: 2,
+        3: 2,
+        4: 3,
+        5: 3,
+        6: 4,
+        7: 4,
+        8: 4,
+        9: 5,
+        10: 5,
+        11: 6,
+        12: 6,
+        13: 6,
+        14: 7,
+        15: 7,
+        16: 8,
+        17: 8,
+        18: 8,
+        19: 9,
+        20: 9,
+        21: 10
+      };
+
+      Object.keys(zoomToGeoHashPrecision).forEach((zoomLevel) => {
+        it(`zoom level ${zoomLevel} should correspond to correct geohash-precision`, () => {
+          const output = {params: {}};
+          paramWriter.write({
+            vis: {
+              hasUiState: () => true,
+              uiStateVal: () => zoomLevel
+            },
+            params: {
+              autoPrecision: true
+            }
+          }, output);
+          expect(output.params.precision).to.equal(zoomToGeoHashPrecision[zoomLevel]);
+        });
+      });
+    });
+
+  });
+});

src/ui/public/agg_types/__tests__/index.js

@@ -4,6 +4,7 @@ import './agg_type';
 import './agg_params';
 import './bucket_count_between';
 import './buckets/_histogram';
+import './buckets/_geo_hash';
 import './buckets/_range';
 import AggTypesIndexProvider from 'ui/agg_types/index';
 import AggTypesBucketsBucketAggTypeProvider from 'ui/agg_types/buckets/_bucket_agg_type';

src/ui/public/agg_types/buckets/geo_hash.js

@@ -1,34 +1,30 @@
 import _ from 'lodash';
-import moment from 'moment';
 import AggTypesBucketsBucketAggTypeProvider from 'ui/agg_types/buckets/_bucket_agg_type';
 import precisionTemplate from 'ui/agg_types/controls/precision.html';
+import {geohashColumns} from 'ui/utils/decode_geo_hash';
+
 export default function GeoHashAggDefinition(Private, config) {
   let BucketAggType = Private(AggTypesBucketsBucketAggTypeProvider);
   let defaultPrecision = 2;
 
-  // zoomPrecision maps event.zoom to a geohash precision value
-  // event.limit is the configurable max geohash precision
-  // default max precision is 7, configurable up to 12
-  const zoomPrecision = {
-    1: 2,
-    2: 2,
-    3: 2,
-    4: 3,
-    5: 3,
-    6: 4,
-    7: 4,
-    8: 5,
-    9: 5,
-    10: 6,
-    11: 6,
-    12: 7,
-    13: 7,
-    14: 8,
-    15: 9,
-    16: 10,
-    17: 11,
-    18: 12
-  };
+  /**
+   * Map Leaflet zoom levels to geohash precision levels.
+   * The size of a geohash column-width on the map should be at least `minGeohashPixels` pixels wide.
+   */
+  let zoomPrecision = {};
+  const minGeohashPixels = 16;
+  for (let zoom = 0; zoom <= 21; zoom += 1) {
+    const worldPixels = 256 * Math.pow(2, zoom);
+    zoomPrecision[zoom] = 1;
+    for (let precision = 2; precision <= 12; precision += 1) {
+      const columns = geohashColumns(precision, 0);
+      if (worldPixels / columns >= minGeohashPixels) {
+        zoomPrecision[zoom] = precision;
+      } else {
+        break;
+      }
+    }
+  }
 
   function getPrecision(precision) {
     let maxPrecision = _.parseInt(config.get('visualization:tileMap:maxPrecision'));
@@ -75,8 +71,11 @@ export default function GeoHashAggDefinition(Private, config) {
         },
         write: function (aggConfig, output) {
           const vis = aggConfig.vis;
-          const currZoom = vis.hasUiState() && vis.uiStateVal('mapZoom');
-          const autoPrecisionVal = zoomPrecision[(currZoom || vis.params.mapZoom)];
+          let currZoom;
+          if (vis.hasUiState()) {
+            currZoom = parseInt(vis.uiStateVal('mapZoom'));
+          }
+          const autoPrecisionVal = zoomPrecision[currZoom >= 0 ? currZoom : parseInt(vis.params.mapZoom)];
           output.params.precision = aggConfig.params.autoPrecision ? autoPrecisionVal : getPrecision(aggConfig.params.precision);
         }
       }

src/ui/public/utils/__tests__/decode_geo_hash.js

@@ -0,0 +1,11 @@
+import expect from 'expect.js';
+import {geohashColumns} from 'ui/utils/decode_geo_hash';
+
+describe('decode_geo_hash', function () {
+  it('geohashColumns', function () {
+    expect(geohashColumns(1)).to.equal(8);
+    expect(geohashColumns(2)).to.equal(8 * 4);
+    expect(geohashColumns(3)).to.equal(8 * 4 * 8);
+    expect(geohashColumns(4)).to.equal(8 * 4 * 8 * 4);
+  });
+});

src/ui/public/utils/decode_geo_hash.js

@@ -56,3 +56,29 @@ function refine_interval(interval, cd, mask) {
 }
 
 export default decodeGeoHash;
+
+
+/**
+ * Get the number of geohash cells for a given precision
+ *
+ * @param {number} precision the geohash precision (1<=precision<=12).
+ * @param {number} axis constant for the axis 0=lengthwise (ie. columns, along longitude), 1=heightwise (ie. rows, along latitude).
+ * @returns {number} Number of geohash cells (rows or columns) at that precision
+ */
+function geohashCells(precision, axis) {
+  let cells = 1;
+  for (let i = 1; i <= precision; i += 1) {
+    //On odd precisions, rows divide by 4 and columns by 8. Vice-versa on even precisions.
+    cells *= (i % 2 === axis) ? 4 : 8;
+  }
+  return cells;
+}
+
+/**
+ * Get the number of geohash columns (world-wide) for a given precision
+ * @param precision the geohash precision
+ * @returns {number} the number of columns
+ */
+export function geohashColumns(precision) {
+  return geohashCells(precision, 0);
+}