diff --git a/istsoslib/renderers/GCresponseRender.py b/istsoslib/renderers/GCresponseRender.py
index f25b6fe0..9366abac 100755
--- a/istsoslib/renderers/GCresponseRender.py
+++ b/istsoslib/renderers/GCresponseRender.py
@@ -292,6 +292,9 @@ def render_2_0_0(GC,sosConfig):
                     r += "        </ows:Range>\n"
                     
                 r += "      </ows:AllowedValues>\n"
+                # add ReferenceSystem tag
+                if p.referenceSystem:
+                    r += "      <ows:ReferenceSystem reference='" + str(p.referenceSystem) + "' />\n"
                 r += "    </ows:Parameter>\n"
                 
             if o.name != 'GlobalOperations':
@@ -427,4 +430,4 @@ def render_2_0_0(GC,sosConfig):
         r += "    </sos:contents>\n" 
         
     r += "    </sos:Capabilities>"
-    return r
\ No newline at end of file
+    return r
diff --git a/istsoslib/responders/GCresponse.py b/istsoslib/responders/GCresponse.py
index fd80e8c0..17e2df17 100755
--- a/istsoslib/responders/GCresponse.py
+++ b/istsoslib/responders/GCresponse.py
@@ -90,11 +90,12 @@ class Parameter:
         allowedValues (list): allowed values
         range (list): ranges
     """
-    def __init__(self,name,use = "optional",allowedValues=[],range=[]):
+    def __init__(self,name,use = "optional",allowedValues=[],range=[], referenceSystem=False):
         self.name=name
         self.use=use
         self.allowedValues=allowedValues
         self.range=range
+        self.referenceSystem=referenceSystem
 
 class Operation:
     """Operation object
@@ -111,8 +112,8 @@ def __init__(self,name,get="",post=""):
         self.get=get
         self.post=post
         self.parameters=[]
-    def addParameter(self,name,use = "optional",allowedValues=[],range=[]):
-        self.parameters.append(Parameter(name,use,allowedValues,range))
+    def addParameter(self,name,use = "optional",allowedValues=[],range=[], referenceSystem=False):
+        self.parameters.append(Parameter(name,use,allowedValues,range,referenceSystem))
 
 def BuildSensorIdList(pgdb,sosConfig):
     """Generate the sensor list
@@ -197,6 +198,9 @@ def BuildEventTimeRange(pgdb,sosConfig):
     return [rows[0]["b"],rows[0]["e"]]
 
 def BuildEnvelopeMinMax(pgdb,sosConfig):
+    sosEpsgList = [sosConfig.istsosepsg,]*2
+    sosSchemaList = [sosConfig.schema,]*3
+    sqlParamsList = sosEpsgList+sosSchemaList+[sosConfig.istsosepsg, sosConfig.schema]
     sql = """
         SELECT 
             st_XMin(envelope) as mix,
@@ -205,10 +209,10 @@ def BuildEnvelopeMinMax(pgdb,sosConfig):
             st_YMax(envelope) as may
         FROM
         (
-        	select ST_ENVELOPE(ST_Collect(ST_Transform(envelope,3857))) as envelope 
+        	select ST_ENVELOPE(ST_Collect(ST_Transform(envelope,%s))) as envelope 
         	from (
         			select 
-        			  ST_ENVELOPE(ST_Collect(ST_Transform(geom_pos,3857))) as envelope 
+        			  ST_ENVELOPE(ST_Collect(ST_Transform(geom_pos,%s))) as envelope 
         			FROM 
         			  %s.positions, %s.event_time, %s.procedures
         			WHERE 
@@ -217,12 +221,12 @@ def BuildEnvelopeMinMax(pgdb,sosConfig):
         			  id_eti = id_eti_fk
         		union
         			select 
-        			  ST_ENVELOPE(ST_Collect(ST_Transform(geom_foi,3857))) as envelope 
+        			  ST_ENVELOPE(ST_Collect(ST_Transform(geom_foi,%s))) as envelope 
         			FROM 
         			  %s.foi
         	) as g
         ) as s
-    """ % ((sosConfig.schema,)*4)
+    """ % (tuple(sqlParamsList))
     result = [0,0,0,0]
     rows=pgdb.select(sql)
     if len(rows) == 1:
@@ -543,7 +547,7 @@ def __init__(self,pgdb,sosConfig):
         GetObservation=Operation(name="GetObservation", get = sosConfig.serviceUrl["get"])
         GetObservation.addParameter(name="offering", use = "required", allowedValues = BuildOfferingList_2_0_0(pgdb,sosConfig))
         GetObservation.addParameter(name="temporalFilter", use = "optional", allowedValues = [], range=BuildEventTimeRange(pgdb,sosConfig))
-        GetObservation.addParameter(name="spatialFilter", use = "optional", allowedValues = [], range=BuildEnvelopeMinMax(pgdb,sosConfig))
+        GetObservation.addParameter(name="spatialFilter", use = "optional", allowedValues = [], range=BuildEnvelopeMinMax(pgdb,sosConfig), referenceSystem="http://www.opengis.net/def/crs/EPSG/0/"+sosConfig.istsosepsg)
         GetObservation.addParameter(name="procedure", use = "optional", allowedValues = BuildSensorIdList(pgdb,sosConfig))
         GetObservation.addParameter(name="observedProperty", use = "optional", allowedValues = BuildobservedPropertyList(pgdb,sosConfig))
         GetObservation.addParameter(name="featureOfInterest", use = "optional", allowedValues = BuildfeatureOfInterestList(pgdb,sosConfig))