From 9d8ce6bc44055c58f5f465d45f2dfdff5e627827 Mon Sep 17 00:00:00 2001
From: Javier Goizueta <jgoizueta@gmail.com>
Date: Thu, 14 Dec 2017 16:51:55 +0100
Subject: [PATCH] Refactor aggregation resolution

---
 .../models/aggregation/aggregation-query.js      | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/lib/cartodb/models/aggregation/aggregation-query.js b/lib/cartodb/models/aggregation/aggregation-query.js
index ca6d3431..332241d8 100644
--- a/lib/cartodb/models/aggregation/aggregation-query.js
+++ b/lib/cartodb/models/aggregation/aggregation-query.js
@@ -78,9 +78,14 @@ const aggregateColumnDefs = ctx => {
     }).join(', ');
 };
 
+
+// SQL expression to compute the aggregation resolution (grid cell size).
+// This is equivalent to `${256/ctx.res}*CDB_XYZ_Resolution(CDB_ZoomFromScale(!scale_denominator!))`
+// This is defined by the ctx.res parameter, which is the number of grid cells per tile linear dimension
+// (i.e. each tile is divided into ctx.res*ctx.res cells).
+const gridResolution = ctx => `(${256*0.00028/ctx.res}*!scale_denominator!)::double precision`;
+
 // Notes:
-// * ${256*0.00028/ctx.res}*!scale_denominator! is equivalent to
-//   ${256/ctx.res}*CDB_XYZ_Resolution(CDB_ZoomFromScale(!scale_denominator!))
 // * We need to filter spatially using !bbox! to make the queries efficient because
 //   the filter added by Mapnik (wrapping the query)
 //   is only applied after the aggregation.
@@ -90,7 +95,7 @@ const aggregationQueryTemplates = {
     'centroid': ctx => `
         WITH _cdb_params AS (
             SELECT
-            (${256*0.00028/ctx.res}*!scale_denominator!)::double precision AS res,
+            ${gridResolution(ctx)} AS res,
             !bbox! AS bbox
         )
         SELECT
@@ -112,7 +117,7 @@ const aggregationQueryTemplates = {
     'point-grid': ctx => `
     WITH _cdb_params AS (
         SELECT
-        (${256*0.00028/ctx.res}*!scale_denominator!)::double precision AS res,
+        ${gridResolution(ctx)} AS res,
         !bbox! AS bbox
     ),
     _cdb_clusters AS (
@@ -133,8 +138,7 @@ const aggregationQueryTemplates = {
     'point-sample': ctx => `
         WITH _cdb_params AS (
             SELECT
-
-            (${256*0.00028/ctx.res}*!scale_denominator!)::double precision AS res,
+            ${gridResolution(ctx)} AS res,
             !bbox! AS bbox
         ), _cdb_clusters AS (
             SELECT