typedef struct {
	double x, y;
} point_xy;
typedef struct {
	double λ, φ;
} point_λφ;

typedef struct projection projection;
typedef struct elliptic elliptic;
struct projection {
	point_λφ o;
	point_xy false;
	double 
		M₀,	/* arc measure to φ₀*/
		k₀;	/* scale at λ₀ */
	point_λφ	(*λφ)(point_xy, elliptic *, projection *);	/* conversion routines */
	point_xy	(*xy)(point_λφ, elliptic *, projection *);
	int (*init)(projection*, elliptic*, char*);
	char *description;
};

struct elliptic {
	double
		a,	/* major axis */
		b,	/* minor axis */
		f,	/* flattening */
		e⁲,	/* first */
		E⁲,	/* second */
		*en;	/* arc params */
};

double lenMarc(double φ, double Sφ, double Cφ, struct elliptic *ell);
double arcMlen(double y, struct elliptic *ell);
double *ell_en_init(struct elliptic *ell);

int get_ell(struct elliptic *ell, char *name);
int get_projection(projection *p, char *name);

int tmin(projection*, elliptic*, char*);
int utmin(projection*, elliptic*, char*);