```--- a
+++ b/src/_op_fwd.cc
@@ -0,0 +1,160 @@
+/* -*- coding: utf-8 -*- */
+/* Copyright (C) 2009  José Luis García Pallero, <jgpallero@gmail.com>
+ *
+ * This file is part of OctPROJ.
+ *
+ * OctPROJ is free software; you can redistribute it and/or modify
+ * the Free Software Foundation; either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this software; see the file COPYING.  If not, see
+ */
+/******************************************************************************/
+/******************************************************************************/
+#define HELPTEXT "\
+-*- texinfo -*-\n\
+_op_fwd(@var{lon},@var{lat},@var{params})\n\
+\n\
+@cindex Performs forward projection step.\n\
+\n\
+This function projects geodetic coordinates into cartesian projected\n\
+coordinates in the defined cartographic projection using the PROJ.4 function \
+pj_fwd().\n\
+\n\
+@var{lon} is a column vector containing the geodetic longitude, in radians.\n\
+@var{lat} is a column vector containing the geodetic latitude, in radians.\n\
+@var{params} is a text string containing the projection parameters in PROJ.4 \
+format.\n\
+\n\
+The coordinate vectors @var{lon} and @var{lat} must be both scalars or both\n\
+column vectors (of the same size).\n\
+\n\
+@var{X} is a column vector containing the X projected coordinates.\n\
+@var{Y} is a column vector containing the Y projected coordinates.\n\
+\n\
+If a projection error occurs, the resultant coordinates for the affected\n\
+points have both Inf value and a warning message is emitted (one for each\n\
+erroneous point).\n\
+@seealso{_op_inv}\n\
+@end deftypefn"
+/******************************************************************************/
+/******************************************************************************/
+#include<octave/oct.h>
+#include<cstdio>
+#include<cstring>
+#include<cstdlib>
+#include<cmath>
+#include"projwrap.h"
+/******************************************************************************/
+/******************************************************************************/
+#define ERRORTEXT 1000
+/******************************************************************************/
+/******************************************************************************/
+DEFUN_DLD(_op_fwd,args,,HELPTEXT)
+{
+    //error message
+    char errorText[ERRORTEXT]="_op_fwd:\n\t";
+    //output list
+    octave_value_list outputList;
+    ////////////////////////////////////////////////////////////////////////////
+    ////////////////////////////////////////////////////////////////////////////
+    //checking input arguments
+    if(args.length()!=3)
+    {
+        //error text
+        sprintf(&errorText[strlen(errorText)],
+                "Incorrect number of input arguments\n\t"
+                "See help _op_fwd");
+        //error message
+        error(errorText);
+    }
+    else
+    {
+        //error code
+        int idErr=0;
+        //error in projection
+        int projectionError=0;
+        //auxiliar message
+        char auxErrorText[ERRORTEXT];
+        //loop index
+        size_t i=0;
+        //geodetic coordinates
+        ColumnVector lon=args(0).column_vector_value();
+        ColumnVector lat=args(1).column_vector_value();
+        //projection parameters
+        std::string params=args(2).string_value();
+        //number of elements
+        size_t nElem=static_cast<size_t>(lon.rows());
+        //projected coordinates
+        ColumnVector xOut(nElem);
+        ColumnVector yOut(nElem);
+        //computation vectors
+        double* x=NULL;
+        double* y=NULL;
+        ////////////////////////////////////////////////////////////////////////
+        ////////////////////////////////////////////////////////////////////////
+        //copy input data
+        for(i=0;i<nElem;i++)
+        {
+            xOut(i) = lon(i);
+            yOut(i) = lat(i);
+        }
+        //pointers to output data
+        x = const_cast<double*>(xOut.data());
+        y = const_cast<double*>(yOut.data());
+        ////////////////////////////////////////////////////////////////////////
+        ////////////////////////////////////////////////////////////////////////
+        //projection
+        idErr = proj_fwd(x,y,nElem,params.c_str(),&errorText[strlen(errorText)],
+                         &projectionError);
+        //error checking
+        if(idErr)
+        {
+            //type of error
+            if(projectionError)
+            {
+                //warning message
+                warning(errorText);
+                //positions of projection errors
+                for(i=0;i<nElem;i++)
+                {
+                    //testing for HUGE_VAL
+                    if((x[i]==HUGE_VAL)&&(y[i]==HUGE_VAL))
+                    {
+                        //error text
+                        sprintf(auxErrorText,
+                             "Projection error in point %d (index starts at 1)",
+                                i+1);
+                        //warning
+                        warning(auxErrorText);
+                    }
+                }
+            }
+            else
+            {
+                //error message
+                error(errorText);
+                //exit
+                return outputList;
+            }
+        }
+        ////////////////////////////////////////////////////////////////////////
+        ////////////////////////////////////////////////////////////////////////
+        //output parameters list
+        outputList(0) = xOut;
+        outputList(1) = yOut;
+    }
+    ////////////////////////////////////////////////////////////////////////////
+    ////////////////////////////////////////////////////////////////////////////
+    //exit
+    return outputList;
+}
```