diff --git a/doc/08_interpolation.md b/doc/08_interpolation.md
index 22fc1bc..c17269e 100644
--- a/doc/08_interpolation.md
+++ b/doc/08_interpolation.md
@@ -2,7 +2,7 @@
 
 Function to interpolate a numeric attribute of a point in a scatter dataset of points, using one of three methos:
 
-* [Nearest neighbor](https://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
+* [Nearest neighbor(s)](https://en.wikipedia.org/wiki/Nearest-neighbor_interpolation)
 * [Barycentric](https://en.wikipedia.org/wiki/Barycentric_coordinate_system)
 * [IDW](https://en.wikipedia.org/wiki/Inverse_distance_weighting)
 
@@ -15,7 +15,7 @@ Function to interpolate a numeric attribute of a point in a scatter dataset of p
 | query   | text | query that returns at least `the_geom` and a numeric value as `attrib` |
 | point   | geometry | The target point to calc the value |
 | method   | integer     | 0:nearest neighbor, 1: barycentric, 2: IDW|
-| p1   | integer     | IDW: limit the number of neighbors, 0->no limit|
+| p1   | integer     | limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one|
 | p2   | integer     | IDW: order of distance decay, 0-> order 1|
 
 ### CDB_SpatialInterpolation (geom geometry[], values numeric[], point geometry, method integer DEFAULT 1, p1 integer DEFAULT 0, ps integer DEFAULT 0)
@@ -28,7 +28,7 @@ Function to interpolate a numeric attribute of a point in a scatter dataset of p
 | values | numeric[]   | Array of points' values for the param under study|
 | point   | geometry | The target point to calc the value |
 | method   | integer     | 0:nearest neighbor, 1: barycentric, 2: IDW|
-| p1   | integer     | IDW: limit the number of neighbors, 0->no limit|
+| p1   | integer     | limit the number of neighbors, IDW: 0->no limit, NN: 0-> closest one|
 | p2   | integer     | IDW: order of distance decay, 0-> order 1|
 
 ### Returns
@@ -37,6 +37,9 @@ Function to interpolate a numeric attribute of a point in a scatter dataset of p
 |-------------|------|-------------|
 | value  | numeric | Interpolated value at the given point, `-888.888` if the given point is out of the boundaries of the source points set |
 
+Default values:
+* -888.888: when using Barycentric, the target point is out of the realm of the input points
+* -777.777: asking for a method not available
 
 #### Example Usage
 
diff --git a/src/pg/sql/08_interpolation.sql b/src/pg/sql/08_interpolation.sql
index 0937f09..cb0a20a 100644
--- a/src/pg/sql/08_interpolation.sql
+++ b/src/pg/sql/08_interpolation.sql
@@ -1,6 +1,8 @@
--- 0: nearest neighbor
+-- 0: nearest neighbor(s)
 -- 1: barymetric
 -- 2: IDW
+-- 3: krigin ---> TO DO
+
 
 CREATE OR REPLACE FUNCTION CDB_SpatialInterpolation(
     IN query text,
@@ -50,12 +52,19 @@ DECLARE
     vc numeric;
     output numeric;
 BEGIN
-    output :=  -999.999;
-    -- nearest
+    -- output :=  -999.999;
+
+    -- nearest neighbors
+    -- p1: limit the number of neighbors, 0-> closest one
     IF method = 0 THEN
 
-        WITH    a as (SELECT unnest(geomin) as g, unnest(colin) as v)
-        SELECT a.v INTO output FROM a ORDER BY point<->a.g LIMIT 1;
+        IF p1 = 0 THEN
+            p1 := 1;
+        END IF;
+
+        WITH    a as (SELECT unnest(geomin) as g, unnest(colin) as v),
+                b as (SELECT a.v as v FROM a ORDER BY point<->a.g LIMIT p1::integer)
+        SELECT avg(b.v) INTO output FROM b;
         RETURN output;
 
     -- barymetric
@@ -121,6 +130,11 @@ BEGIN
         SELECT sum(b.f)/sum(b.k) INTO output FROM b;
         RETURN output;
 
+    -- krigin
+    ELSIF method = 3 THEN
+
+    --  TO DO
+
     END IF;
 
     RETURN -777.777;
diff --git a/src/pg/test/expected/08_interpolation_test.out b/src/pg/test/expected/08_interpolation_test.out
index 1e4502a..e2c9287 100644
--- a/src/pg/test/expected/08_interpolation_test.out
+++ b/src/pg/test/expected/08_interpolation_test.out
@@ -1,7 +1,7 @@
 SET client_min_messages TO WARNING;
 \set ECHO none
- nn  |           nni            |       idw       
------+--------------------------+-----------------
- 200 | 238.41059602632179224595 | 341.46260750526
+          nn          |           nni            |       idw       
+----------------------+--------------------------+-----------------
+ 200.0000000000000000 | 238.41059602632179224595 | 341.46260750526
 (1 row)