Cluster: Use new webmercator utilities

lib/cartodb/backends/cluster.js

@@ -5,6 +5,9 @@ const dbParamsFromReqParams = require('../utils/database-params');
 const debug = require('debug')('backend:cluster');
 const AggregationMapConfig = require('../models/aggregation/aggregation-mapconfig');
 
+const windshaftUtils = require('windshaft').utils;
+const wmh = new windshaftUtils.WebMercatorHelper();
+
 module.exports = class ClusterBackend {
     getClusterFeatures (mapConfigProvider, params, callback) {
         mapConfigProvider.getMapConfig((err, _mapConfig) => {
@@ -156,8 +159,8 @@ const clusterFeaturesQuery = ctx => `
 `;
 
 const gridResolution = ctx => {
-    const minimumResolution = 2*Math.PI*6378137/Math.pow(2,38);
-    return `${256/ctx.res} * GREATEST(!pixel_height!, ${minimumResolution})::numeric`;
+    const zoom_resolution = wmh.getResolution({ z : Math.min(38, ctx.zoom) });
+    return `${256/ctx.res} * (${zoom_resolution})::double precision`;
 };
 
 const aggregationQuery = ctx => `

lib/cartodb/models/aggregation/aggregation-query.js

@@ -429,7 +429,7 @@ SELECT * FROM
             OFFSET 0
         ) __cdb_src_get_x_y, __cdb_grid_params
         WHERE cdb_x < __cdb_grid_params.cdb_xmax AND cdb_y < __cdb_grid_params.cdb_ymax
-    ) __cdb_src_gridded, __cdb_grid_params
+    ) __cdb_src_gridded
     GROUP BY cdb_pos_grid_x, cdb_pos_grid_y ${dimensionNames(ctx)}
     ${havingClause(ctx)}
 ) __cdb_aggregation_src