add base logick + 1 test

Author: stepan-neretin7

expected/points.out

@@ -385,6 +385,17 @@ SELECT long('(24h 2m 30s ,-90d 0m 0s)'::spoint);
  0.01090830782496
 (1 row)
 
+-- get_gravity_center(array(spoint))
+SELECT get_gravity_center(ARRAY[
+    spoint(40.7128, -74.0060),
+    spoint(34.0522, -118.2437),
+    spoint(37.7749, -122.4194)
+]);
+    get_gravity_center    
+--------------------------
+ (3.0436698 , 0.85893807)
+(1 row)
+
 -- lat(spoint)
 SELECT lat('( 0h 2m 30s , 0d 0m 0s)'::spoint);
  lat 

pgs_point.sql.in

@@ -167,3 +167,8 @@ CREATE OPERATOR  <-> (
 COMMENT ON OPERATOR <-> (spoint, spoint) IS
   'distance between spherical points';
 
+CREATE FUNCTION get_gravity_center(dots_vector SPoint[])
+   RETURNS spoint
+   AS 'MODULE_PATHNAME', 'get_gravity_center'
+   LANGUAGE 'c'
+   IMMUTABLE STRICT PARALLEL SAFE;

sql/points.sql

@@ -138,6 +138,14 @@ SELECT long('(24h 2m 30s ,90d 0m 0s)'::spoint);
 
 SELECT long('(24h 2m 30s ,-90d 0m 0s)'::spoint);
 
+-- get_gravity_center(array(spoint))
+SELECT get_gravity_center(ARRAY[
+    spoint(40.7128, -74.0060),
+    spoint(34.0522, -118.2437),
+    spoint(37.7749, -122.4194)
+]);
+
+
 -- lat(spoint)
 
 SELECT lat('( 0h 2m 30s , 0d 0m 0s)'::spoint);

src/point.c

@@ -12,6 +12,7 @@ PG_FUNCTION_INFO_V1(spherepoint_y);
 PG_FUNCTION_INFO_V1(spherepoint_z);
 PG_FUNCTION_INFO_V1(spherepoint_xyz);
 PG_FUNCTION_INFO_V1(spherepoint_equal);
+PG_FUNCTION_INFO_V1(get_gravity_center);
 
 bool
 spoint_eq(const SPoint *p1, const SPoint *p2)
@@ -263,3 +264,40 @@ spherepoint_equal(PG_FUNCTION_ARGS)
 
 	PG_RETURN_BOOL(spoint_eq(p1, p2));
 }
+
+static SPoint * spherepoint_from_vector3d(Vector3D v){
+	SPoint* p = (SPoint *) palloc(sizeof(SPoint));
+	p->lat = asin(v.z / sqrt(pow(v.x, 2) + pow(v.y, 2)  + pow(v.z, 2)));
+	p->lng = atan2(v.y, v.x);
+	return p;
+}
+
+Datum get_gravity_center(PG_FUNCTION_ARGS) {
+	SPoint * p;
+	SPoint current_point;
+	Vector3D	v;
+	Vector3D	res;
+	ArrayType *dots_vector = PG_GETARG_ARRAYTYPE_P(0);
+	int num_elements = ArrayGetNItems(ARR_NDIM(dots_vector), ARR_DIMS(dots_vector));
+	SPoint *array_data = (SPoint *) ARR_DATA_PTR(dots_vector);
+
+	for (int i = 0; i < num_elements; i++) {
+		current_point = array_data[i];
+		//elog(LOG, "%lf\n", current_point.lat);
+		spoint_vector3d(&v, &current_point);
+		elog(LOG, "%lf\n", v.x);
+		res.x+=v.x;
+		res.y+=v.y;
+		res.z+=v.z;
+	}
+
+	res.x /= num_elements;
+	res.y /= num_elements;
+	res.z /= num_elements;
+
+	p = spherepoint_from_vector3d(res);
+
+	spoint_check(p);
+
+	PG_RETURN_POINTER(p);
+}

src/point.h

@@ -90,4 +90,9 @@ Datum	spherepoint_xyz(PG_FUNCTION_ARGS);
  */
 Datum	spherepoint_equal(PG_FUNCTION_ARGS);
 
+/*
+ * Return gravity center from array of spherical points
+ */
+Datum get_gravity_center(PG_FUNCTION_ARGS);
+
 #endif