Use bounding box of dataviews to select overviews level

lib/cartodb/backends/dataview.js

@@ -136,13 +136,17 @@ DataviewBackend.prototype.getDataview = function (mapConfigProvider, user, param
                     );
                 }
             }
-            var dataviewFactory = DataviewFactoryWithOverviews.getFactory(overviewsQueryRewriter, queryRewriteData);
 
             if (params.bbox) {
                 var bboxFilter = new BBoxFilter({column: 'the_geom', srid: 4326}, {bbox: params.bbox});
                 query = bboxFilter.sql(query);
+                queryRewriteData = _.extend(queryRewriteData, { bbox_filter: bboxFilter });
             }
 
+            var dataviewFactory = DataviewFactoryWithOverviews.getFactory(
+                overviewsQueryRewriter, queryRewriteData, { bbox: params.bbox }
+            );
+
             var overrideParams = _.reduce(_.pick(params, 'start', 'end', 'bins'),
                 function castNumbers(overrides, val, k) {
                     overrides[k] = Number.isFinite(+val) ? +val : val;

lib/cartodb/models/dataview/overviews/factory.js

@@ -1,9 +1,10 @@
 var parentFactory = require('../factory');
 var dataviews = require('./');
 
-function OverviewsDataviewFactory(queryRewriter, queryRewriteData) {
+function OverviewsDataviewFactory(queryRewriter, queryRewriteData, options) {
     this.queryRewriter = queryRewriter;
     this.queryRewriteData = queryRewriteData;
+    this.options = options;
 }
 
 OverviewsDataviewFactory.prototype.getDataview = function(query, dataviewDefinition) {
@@ -12,7 +13,9 @@ OverviewsDataviewFactory.prototype.getDataview = function(query, dataviewDefinit
     if ( !this.queryRewriter || !this.queryRewriteData || !dataviews[type] ) {
         return parentFactory.getDataview(query, dataviewDefinition);
     }
-    return new dataviews[type](query, dataviewDefinition.options, this.queryRewriter, this.queryRewriteData);
+    return new dataviews[type](
+        query, dataviewDefinition.options, this.queryRewriter, this.queryRewriteData, this.options
+    );
 };
 
 var OverviewsDataviewMetaFactory = {
@@ -21,8 +24,8 @@ var OverviewsDataviewMetaFactory = {
         return allDataviews;
     }, {}),
 
-    getFactory: function(queryRewriter, queryRewriteData) {
-        return new OverviewsDataviewFactory(queryRewriter, queryRewriteData);
+    getFactory: function(queryRewriter, queryRewriteData, options) {
+        return new OverviewsDataviewFactory(queryRewriter, queryRewriteData, options);
     },
 };
 

lib/cartodb/models/dataview/overviews/formula.js

@@ -1,3 +1,4 @@
+var _ = require('underscore');
 var BaseWidget = require('../base');
 var BaseDataview = require('../formula');
 
@@ -27,13 +28,14 @@ var formulaQueryTpls = {
   ].join('\n')),
 };
 
-function Formula(query, options, queryRewriter, queryRewriteData) {
+function Formula(query, options, queryRewriter, queryRewriteData, params) {
     this.base_dataview = new BaseDataview(query, options);
     this.query = query;
     this.column = options.column || '1';
     this.operation = options.operation;
     this.queryRewriter = queryRewriter;
     this.queryRewriteData = queryRewriteData;
+    this.options = params;
 }
 
 Formula.prototype = new BaseWidget();
@@ -41,21 +43,39 @@ Formula.prototype.constructor = Formula;
 
 module.exports = Formula;
 
+var zoom_level_factor = 100.0;
+
+// Compute zoom level so that the the resolution grid size of the
+// selected overview is smaller (zoom_level_factor times smaller at least)
+// than the bounding box size.
+function zoom_level_for_bbox(bbox) {
+    var px_per_tile = 256.0;
+    var earth_width = 360.0;
+    // TODO: now we assume overviews are computed for 1-pixel tolerance;
+    // should use extended overviews metadata to compute this properly.
+    if ( bbox ) {
+      var bbox_values = _.map(bbox.split(','), function(v) { return +v; });
+      // TODO: look at possible crossing-180º issues
+      var w = Math.abs(bbox_values[2]-bbox_values[0]);
+      var h = Math.abs(bbox_values[3]-bbox_values[1]);
+      var max_dim = Math.min(w, h);
+
+      // Find minimum suitable z
+      // note that the QueryRewirter will use the minimum level overview
+      // of level >= z if it exists, and otherwise the base table
+      var z = Math.ceil(-Math.log(max_dim*px_per_tile/earth_width/zoom_level_factor)/Math.log(2.0));
+      return Math.max(z, 0);
+    }
+    return 0;
+}
+
 Formula.prototype.sql = function(psql, filters, override, callback) {
     var _query = this.query;
     var formulaQueryTpl = formulaQueryTpls[this.operation];
 
     if ( formulaQueryTpl ) {
         // supported formula for use with overviews
-
-        // TODO: determine zoom level using bounding box so that the resolution
-        // (grid size) of the overview much smaller thatn the bounding box.
-        // This could be left to be computed by the queryRewriter passing the
-        // bounding box to it.
-        // The bounding box could be passed to the dataview constructor, or
-        // it could b extracted from the query.
-        var zoom_level = 0;
-
+        var zoom_level = zoom_level_for_bbox(this.options.bbox);
         _query = this.queryRewriter.query(_query, this.queryRewriteData, { zoom_level: zoom_level });
         var formulaSql = formulaQueryTpl({
             _query: _query,
@@ -64,6 +84,7 @@ Formula.prototype.sql = function(psql, filters, override, callback) {
         });
         debug(formulaSql);
         callback = callback || override;
+
         return callback(null, formulaSql);
     }
 

lib/cartodb/utils/overviews_query_rewriter.js

@@ -3,11 +3,14 @@ var TableNameParser = require('./table_name_parser');
 
 // this is meant as a hack for development
 var queryBuilder = require('camshaft/lib/filter/query-builder');
-function apply_filters_to_query(query, filters) {
+function apply_filters_to_query(query, filters, bbox_filter) {
     // TODO: implement filter application here
     if ( filters && !_.isEmpty(filters)) {
         query = queryBuilder.getSql(query, filters);
     }
+    if ( bbox_filter ) {
+        query = bbox_filter.sql(query);
+    }
     return query;
 }
 
@@ -227,6 +230,7 @@ OverviewsQueryRewriter.prototype.query = function(query, data, options) {
     var overviews        = data && data.overviews;
     var unfiltered_query = data && data.unfiltered_query;
     var filters          = data && data.filters;
+    var bbox_filter      = data && data.bbox_filter;
 
     if ( !unfiltered_query ) {
         unfiltered_query = query;
@@ -252,7 +256,7 @@ OverviewsQueryRewriter.prototype.query = function(query, data, options) {
         // Applicability of the filters should depend both on the expected
         // row count of the result and on the columns to be filter and the
         // way they're agregated in overviews.
-        rewritten_query = apply_filters_to_query(rewritten_query, filters);
+        rewritten_query = apply_filters_to_query(rewritten_query, filters, bbox_filter);
     }
 
     return rewritten_query;