diff --git a/sources/core/common.h b/sources/core/common.h
index 12c9c6bbb2c1406c0329a429bca2f3819398c691..e6273eabe06c8b3b20f1830116049333c4fd175e 100644
--- a/sources/core/common.h
+++ b/sources/core/common.h
@@ -281,7 +281,7 @@ throw
 
 // Mathematical definition not provided on the Window plateform
 #ifdef _WIN32
-#define M_PI 3.14159265
+#define M_PI 3.1415926535897932384626433832795
 
 template<typename T> bool isnan(T x)
 {
diff --git a/sources/core/data.h b/sources/core/data.h
index 5c7dae270860cc66a414e1ee8c79b409eb62804d..17ad348c50a5c96f0ec84fe057f00b729fe24502 100644
--- a/sources/core/data.h
+++ b/sources/core/data.h
@@ -58,25 +58,19 @@ class data : public parametrized
 		// Acces to data
 		virtual vec get(int i) const = 0 ;
 		virtual vec operator[](int i) const = 0 ;
-		
-		/*
-		//! \brief Provide an evaluation in a BRDF way of the data. 
-		//!
-		//! \details
-		//! The input vector in (can have texture coordinate) and the output
-        //! vector out are taken to grab a value and return it. The two vectors
-		//! should be compliant with the size and parametrization of the data.
-		virtual vec value(vec in, vec out) const = 0;
-		*/
-
-        //! \brief Provide an evaluation in a BRDF way of the data.
+
+        //! \brief Provide an evaluation of the data using interpolation. If
+        //! the data object does not provide an interpolation mechanism, it
+        //! should throw an exception.
         //!
         //! \details
-        //! The input vector must have the parametrization of the data.
-        virtual vec value(vec in) const = 0;
+        //! The input vector must have the parametrization of the data, and
+        //! match the total dimension: dimX + dimY.
+        virtual vec value(const vec& in) const = 0;
 
 		//! \brief Put the sample inside the data
-		virtual void set(vec x) = 0;
+		virtual void set(const vec& x) = 0;
+		virtual void set(int i, const vec& x) = 0;
 
 
 		// Get data size, e.g. the number of samples to fit
@@ -130,11 +124,7 @@ class data_params : public data
 			save(std::string("cluster.gnuplot"));
 		}
 
-		virtual vec value(vec, vec) const 
-		{
-			NOT_IMPLEMENTED();
-		}
-		virtual vec value(vec) const
+		virtual vec value(const vec&) const
 		{
 			NOT_IMPLEMENTED();
 		}
@@ -163,11 +153,16 @@ class data_params : public data
 		}
 
 		//! \todo This should crash at execution.
-		virtual void set(vec x)
+		virtual void set(const vec& x)
 		{
 			this->set(x);
 		}
 
+		virtual void set(int i, const vec& x)
+		{
+			this->set(i, x);
+		}
+
 		// Get data size, e.g. the number of samples to fit
 		virtual int size() const
 		{
diff --git a/sources/core/params.h b/sources/core/params.h
index 0f28c89f99fbcfe97d0089e55e150811b88bb47f..e33fcd89d12dd299c3e93b791c7878bb6e853cf4 100644
--- a/sources/core/params.h
+++ b/sources/core/params.h
@@ -369,6 +369,12 @@ class params
 class parametrized
 {
 	public:
+		parametrized(params::input in_param, params::output out_param) {
+			_in_param  = in_param;
+			_out_param = out_param;
+			_nX = params::dimension(_in_param);
+			_nY = params::dimension(_out_param);
+		}
 		parametrized() : _in_param(params::UNKNOWN_INPUT), 
 		                 _out_param(params::UNKNOWN_OUTPUT) { }
 
diff --git a/sources/core/vertical_segment.cpp b/sources/core/vertical_segment.cpp
index 605a2857973caafd8f79663fdd7df9caa3debcea..227e88e4553c1e338417b2ff809aea5d56157bcc 100644
--- a/sources/core/vertical_segment.cpp
+++ b/sources/core/vertical_segment.cpp
@@ -286,12 +286,18 @@ vec vertical_segment::get(int i) const
 
 //! \todo Check the vertical segment size and if the data
 //! is not already present.
-void vertical_segment::set(vec x)
+void vertical_segment::set(const vec& x)
 {
 //	assert(x.size() == dimX() + dimY() || x.size() == dimX() + 3*dimY());
 	_data.push_back(x);
 }
 
+void vertical_segment::set(int i, const vec& x)
+{
+//	assert(x.size() == dimX() + dimY() || x.size() == dimX() + 3*dimY());
+	_data[i] = x;
+}
+
 int vertical_segment::size() const
 {
 	return _data.size() ;
diff --git a/sources/core/vertical_segment.h b/sources/core/vertical_segment.h
index dc989f2cbf673c283d3827eaea1e992503639f4a..a524e92b912fac0fd045fc39842178c8d22ee648 100644
--- a/sources/core/vertical_segment.h
+++ b/sources/core/vertical_segment.h
@@ -90,18 +90,16 @@ class vertical_segment : public data
 
 		// Acces to data
 		virtual vec get(int i) const ;		
-		virtual vec operator[](int i) const ;
-		virtual vec value(vec, vec) const 
-		{
-			NOT_IMPLEMENTED();
-		}
-        virtual vec value(vec) const
+		virtual vec operator[](int i) const;
+
+        virtual vec value(const vec&) const
         {
             NOT_IMPLEMENTED();
         }
 
 		//! \brief Put the sample inside the data
-		virtual void set(vec x);
+		virtual void set(const vec& x);
+		virtual void set(int i, const vec& x);
 		
 		//! \brief Specific accessor to a vertical segment, this gives the
 		//! complete vector, plus the ordinate segment
diff --git a/sources/plugins/SConscript b/sources/plugins/SConscript
index ddffdb2c2442f9293e4b24453fdbffd4d33f969c..46f148390961a8620a1be779e3db5db3588baf7f 100644
--- a/sources/plugins/SConscript
+++ b/sources/plugins/SConscript
@@ -2,6 +2,7 @@
 SConscript('data_merl/SConscript')
 SConscript('data_brdf_slice/SConscript')
 SConscript('data_interpolant/SConscript')
+#SConscript('data_io/SConscript')
 
 # # Building nonlinear fitters
 SConscript('nonlinear_fitter_ceres/SConscript')
@@ -31,6 +32,7 @@ SConscript('rational_fitter_leastsquare/SConscript')
 SConscript('rational_fitter_quadprog/SConscript')
 SConscript('rational_fitter_parallel/SConscript')
 SConscript('rational_fitter_matlab/SConscript')
+SConscript('rational_fitters/SConscript')
 
 
 # # Building rational functions
diff --git a/sources/plugins/data_astm/data.cpp b/sources/plugins/data_astm/data.cpp
index 2bc20914f828fbaa252ba06fb1dc75163a57b7d4..8608490f012d0c008ad6d5b0ef8072d264bce49f 100644
--- a/sources/plugins/data_astm/data.cpp
+++ b/sources/plugins/data_astm/data.cpp
@@ -66,7 +66,7 @@ void data_astm::load(const std::string& filename, const arguments& args)
 }
 
 // Acces to data
-vec data_astm::get(int i) const 
+vec& data_astm::get(int i) 
 {
 	return _data[i];
 }
diff --git a/sources/plugins/data_astm/data.h b/sources/plugins/data_astm/data.h
index 799beaac117cd2e5aa0d458fe0ffece23c1705d0..621623c488bf606ece81a2b7e52f5ecbf553574a 100644
--- a/sources/plugins/data_astm/data.h
+++ b/sources/plugins/data_astm/data.h
@@ -28,7 +28,7 @@ class data_astm : public QObject, public data
 
 		// Acces to data
 		virtual vec get(int i) const ;
-		virtual vec operator[](int i) const ;
+		virtual vec& operator[](int i) ;
 		virtual vec value(vec in, vec out) const ;
 
 		// Get data size, e.g. the number of samples to fit
diff --git a/sources/plugins/data_brdf_slice/EXR_IO.h b/sources/plugins/data_brdf_slice/EXR_IO.h
index a7bd2b281bbb706ed9c934fb3a5ea622143cedab..941c09bfd8a16c48600aab2f762988d081acc048 100644
--- a/sources/plugins/data_brdf_slice/EXR_IO.h
+++ b/sources/plugins/data_brdf_slice/EXR_IO.h
@@ -10,6 +10,10 @@
 
 #ifndef EXR_IO_H_
 #define EXR_IO_H_
+/*
+ * Author: Cyril Soler
+ */
+
 
 #include <stdexcept>
 
diff --git a/sources/plugins/data_brdf_slice/data.cpp b/sources/plugins/data_brdf_slice/data.cpp
index 87bb1dc58ad1027470046737e09294b48f8cabe5..c66ef88e16c851ee5698c9ca7d3d5709a50b0929 100644
--- a/sources/plugins/data_brdf_slice/data.cpp
+++ b/sources/plugins/data_brdf_slice/data.cpp
@@ -78,7 +78,7 @@ vec data_brdf_slice::operator[](int i) const
 }
 
 //! \todo Test this function
-void data_brdf_slice::set(vec x)
+void data_brdf_slice::set(const vec& x)
 {
 	assert(x.size() == 6);
 	assert(x[0] <= 0.5*M_PI && x[0] >= 0.0);
@@ -93,13 +93,16 @@ void data_brdf_slice::set(vec x)
 	_data[3*id + 1] = x[4];
 	_data[3*id + 2] = x[5];
 }
-
-vec data_brdf_slice::value(vec, vec) const
+void data_brdf_slice::set(int id, const vec& x)
 {
-	vec res(3);
-	return res;
+	assert(x.size() == 3);
+
+	_data[3*id + 0] = x[0];
+	_data[3*id + 1] = x[1];
+	_data[3*id + 2] = x[2];
 }
-vec data_brdf_slice::value(vec x) const
+
+vec data_brdf_slice::value(const vec& x) const
 {
 	assert(x[0] <= 0.5*M_PI && x[0] >= 0.0);
 	assert(x[1] <= 0.5*M_PI && x[1] >= 0.0);
diff --git a/sources/plugins/data_brdf_slice/data.h b/sources/plugins/data_brdf_slice/data.h
index 0e04abfdf0499035d6a22f63c745b9fbeb84926b..d89a6fd419e633ca2e7bfacb9e6c479598239732 100644
--- a/sources/plugins/data_brdf_slice/data.h
+++ b/sources/plugins/data_brdf_slice/data.h
@@ -31,11 +31,11 @@ class data_brdf_slice : public data
 		virtual vec get(int i) const ;
 		virtual vec operator[](int i) const ;
 
-		virtual vec value(vec in, vec out) const;
-		virtual vec value(vec x) const;
+		virtual vec value(const vec& x) const;
 
 		// Set data
-		virtual void set(vec x);
+		virtual void set(int i, const vec& x);
+		virtual void set(const vec& x);
 
 		// Get data size, e.g. the number of samples to fit
 		virtual int size() const ;
diff --git a/sources/plugins/data_merl/data.cpp b/sources/plugins/data_merl/data.cpp
index c0fa283c6b26d89d1c929b3c9c130337e135324e..e77d931cfedb377ef6519c9375feb3238b54979c 100644
--- a/sources/plugins/data_merl/data.cpp
+++ b/sources/plugins/data_merl/data.cpp
@@ -342,13 +342,13 @@ vec data_merl::get(int i) const
 	res[5] = brdf[i + BRDF_SAMPLING_RES_THETA_H*BRDF_SAMPLING_RES_THETA_D*BRDF_SAMPLING_RES_PHI_D] * BLUE_SCALE;
 	return res ;
 }
-vec data_merl::operator[](int i) const 
+vec data_merl::operator[](int i) const
 {
 	return get(i) ;
 }
 
 //! \todo Test this function
-void data_merl::set(vec x)
+void data_merl::set(const vec& x)
 {
 	assert(x.size() == 6);
 	const int phid_ind = phi_diff_index(x[2]);
@@ -366,7 +366,15 @@ void data_merl::set(vec x)
 	brdf[i + BRDF_SAMPLING_RES_THETA_H*BRDF_SAMPLING_RES_THETA_D*BRDF_SAMPLING_RES_PHI_D] = x[5] / BLUE_SCALE;
 }
 
-vec data_merl::value(vec in) const
+void data_merl::set(int i, const vec& x)
+{
+	assert(x.size() == 3);
+	brdf[i] = x[0] / RED_SCALE;
+	brdf[i + BRDF_SAMPLING_RES_THETA_H*BRDF_SAMPLING_RES_THETA_D*BRDF_SAMPLING_RES_PHI_D/2] = x[1] / GREEN_SCALE;
+	brdf[i + BRDF_SAMPLING_RES_THETA_H*BRDF_SAMPLING_RES_THETA_D*BRDF_SAMPLING_RES_PHI_D] = x[2] / BLUE_SCALE;
+}
+
+vec data_merl::value(const vec& in) const
 {
     double r, g, b;
     lookup_brdf_val(brdf, in[0], in[1], in[2], r, g, b) ;
diff --git a/sources/plugins/data_merl/data.h b/sources/plugins/data_merl/data.h
index 4d96a49cb61dc88bac91f347ad759a043b62c243..0c0d81d7ca3d4d98a6f7b66f0593e4cf177ab1d0 100644
--- a/sources/plugins/data_merl/data.h
+++ b/sources/plugins/data_merl/data.h
@@ -27,13 +27,14 @@ class data_merl : public data
 		virtual void save(const std::string& filename) const ;
 
 		// Acces to data
-		virtual vec get(int i) const ;
-		virtual vec operator[](int i) const ;
+		virtual vec get(int i) const;
+		virtual vec operator[](int i) const;
 
-      virtual vec value(vec in) const;
+      virtual vec value(const vec& in) const;
 		
 		// Set data
-		virtual void set(vec x);
+		virtual void set(int i, const vec& x);
+		virtual void set(const vec& x);
 
 		// Get data size, e.g. the number of samples to fit
 		virtual int size() const ;
diff --git a/sources/python/alta.cpp b/sources/python/alta.cpp
index 6d81eeb260612140eeed2d1c103092257858d5e9..c788de7525972de3162af54bf745441817577ffc 100644
--- a/sources/python/alta.cpp
+++ b/sources/python/alta.cpp
@@ -155,7 +155,7 @@ BOOST_PYTHON_MODULE(alta)
 	bp::class_<data, ptr<data>, boost::noncopyable>("data", bp::no_init)
 		.def("size", &data::size)
 		.def("get",  &data::get)
-		.def("set",  &data::set)
+		//.def("set",  &data::set)
 		.def("load", static_cast< void(data::*)(const std::string&)>(&data::load))
 		.def("save", &data::save);
 	bp::def("get_data",  plugins_manager::get_data);
diff --git a/sources/softs/SConscript b/sources/softs/SConscript
index 13d68410f781c24e330e75ac07a0ed42cd4a0869..71aff6523ac797d597943e994923a93e7dba0cfa 100644
--- a/sources/softs/SConscript
+++ b/sources/softs/SConscript
@@ -4,4 +4,6 @@ SConscript('data2moments/SConscript')
 
 SConscript('brdf2brdf/SConscript')
 SConscript('brdf2data/SConscript')
-SConscript('brdf2gnuplot/SConscript')
\ No newline at end of file
+SConscript('brdf2gnuplot/SConscript')
+
+#SConscript('tests/SConscript')
diff --git a/sources/softs/brdf2data/main.cpp b/sources/softs/brdf2data/main.cpp
index 1c849402228483f7979895308edfd58b1da7ae77..a7dabe625670c27519ef7a711394c5728665f8fa 100644
--- a/sources/softs/brdf2data/main.cpp
+++ b/sources/softs/brdf2data/main.cpp
@@ -95,6 +95,11 @@ int main(int argc, char** argv)
 
 	if(d && f != NULL)
 	{
+		// Is the output data file already allocated and has the same size
+		// than the training data ?
+		const bool out_filled = d->size() == d_out->size();
+		const bool output_dif = args.is_defined("export-diff");
+
 		vec temp(f->dimX());
 		for(int i=0; i<d->size(); ++i)
 		{
@@ -111,12 +116,17 @@ int main(int argc, char** argv)
 			}
 			vec y = f->value(temp);
 
-			for(int j=0; j<d->dimY(); ++j)
-			{
-				x[d->dimX() + j] = y[j];
+			for(int j=0; j<d->dimY(); ++j) {
+				x[d->dimX() + j] = (output_dif) ? x[d->dimX() + j] - y[j] : y[j];
 			}
 
-            d_out->set(x);
+			// If the output data is already allocated and has the same size
+			// than the training data, we do simple copy of the index elements.
+			if(out_filled) {
+				d_out->set(i, y);
+			} else {
+            	d_out->set(x);
+            }
 		}	
 
         d_out->save(args["output"]);
diff --git a/sources/softs/tests/main.cpp b/sources/softs/tests/main.cpp
index 028683f21947b0c760cb0872dbd367132fe03b18..301c6dc9a456816e0966a97b72530b1bcfd705d4 100644
--- a/sources/softs/tests/main.cpp
+++ b/sources/softs/tests/main.cpp
@@ -1,3 +1,4 @@
+
 /* ALTA --- Analysis of Bidirectional Reflectance Distribution Functions
 
    Copyright (C) 2013 Inria
@@ -8,6 +9,29 @@
    License, v. 2.0.  If a copy of the MPL was not distributed with this
    file, You can obtain one at http://mozilla.org/MPL/2.0/.  */
 
+#include <core/param.h>
+
+int main(int argc, char** argv) {
+
+	spherical sphericalParam;
+	isotropic_tl_tv isotropicParam;
+
+	vec in(4);
+	in[0] = 0.0;
+	in[1] = 0.0;
+	in[2] = 0.0;
+	in[3] = 0.0;
+
+	vec out(2);
+	sphericalParam.convert_to(in, isotropicParam, out);
+
+	return 0;
+}
+
+
+#ifdef OLD
+
+
 #include <core/args.h>
 #include <core/data.h>
 #include <core/function.h>
@@ -208,3 +232,5 @@ int parametrization_tests()
 */
 	return nb_tests_failed;
 }
+
+#endif