// Error
ldf.h:16:8: erro: redefinition of ‘struct Data’
sphericalfit.h:17:8: erro: previous definition of ‘struct Data’

// sphericalfit.h

#ifndef SPHERICALFIT_H
#define SPHERICALFIT_H

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_vector.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_multifit_nlin.h>
#include <gsl/gsl_sf_gamma.h>
#include <gsl/gsl_blas.h>

#define MAXITER    50000 // Maximum number of tries
#define LIGHTSPEED 0.299792458

struct Data
{
    size_t Stations;

    double * dX;
    double * dY;
    double * dT;

    double dSigma;
};


int sphericalfit(gsl_vector *pData, gsl_vector *pLinFit, gsl_vector *pResult);

#endif


// ldf.h

#ifndef LDF_H
#define LDF_H

#include <cstdio>
#include <cstdlib>
#include <cmath>
#include <gsl/gsl_errno.h>
#include <gsl/gsl_vector.h>
#include <gsl/gsl_matrix.h>
#include <gsl/gsl_multifit_nlin.h>
#include <gsl/gsl_sf_gamma.h>
#include <gsl/gsl_blas.h>

#define MAXITER    50000 // Maximum number of tries

struct Data
{
  size_t Stations;
  
  double *Xi;
  double *Yi;
  double *Si;
  double u;
  double v;

  double Sigma;

};

int ldf(gsl_vector *pData, gsl_vector *pSphData, gsl_vector *pResult);

#endif