/Proj4/PJ_eck4.c

http://github.com/route-me/route-me · C · 47 lines · 45 code · 2 blank · 0 comment · 5 complexity · a6d24e3fbfe0f994db7dff15595f2caf MD5 · raw file 

    

  1. #ifndef lint
    2. 

  2. static const char SCCSID[]="@(#)PJ_eck4.c	4.1	94/02/15	GIE	REL";
    3. 

  3. #endif
    4. 

  4. #define PJ_LIB__
    5. 

  5. #include	"projects.h"
    6. 

  6. PROJ_HEAD(eck4, "Eckert IV") "\n\tPCyl, Sph.";
    7. 

  7. #define C_x	.42223820031577120149
    8. 

  8. #define C_y	1.32650042817700232218
    9. 

  9. #define RC_y	.75386330736002178205
    10. 

  10. #define C_p	3.57079632679489661922
    11. 

  11. #define RC_p	.28004957675577868795
    12. 

  12. #define EPS	1e-7
    13. 

  13. #define NITER	6
    14. 

  14. FORWARD(s_forward); /* spheroid */
    15. 

  15. 	double p, V, s, c;
    16. 

  16. 	int i;
    17. 

  17. 

  18. 	p = C_p * sin(lp.phi);
    19. 

  19. 	V = lp.phi * lp.phi;
    20. 

  20. 	lp.phi *= 0.895168 + V * ( 0.0218849 + V * 0.00826809 );
    21. 

  21. 	for (i = NITER; i ; --i) {
    22. 

  22. 		c = cos(lp.phi);
    23. 

  23. 		s = sin(lp.phi);
    24. 

  24. 		lp.phi -= V = (lp.phi + s * (c + 2.) - p) /
    25. 

  25. 			(1. + c * (c + 2.) - s * s);
    26. 

  26. 		if (fabs(V) < EPS)
    27. 

  27. 			break;
    28. 

  28. 	}
    29. 

  29. 	if (!i) {
    30. 

  30. 		xy.x = C_x * lp.lam;
    31. 

  31. 		xy.y = lp.phi < 0. ? -C_y : C_y;
    32. 

  32. 	} else {
    33. 

  33. 		xy.x = C_x * lp.lam * (1. + cos(lp.phi));
    34. 

  34. 		xy.y = C_y * sin(lp.phi);
    35. 

  35. 	}
    36. 

  36. 	return (xy);
    37. 

  37. }
    38. 

  38. INVERSE(s_inverse); /* spheroid */
    39. 

  39. 	double c;
    40. 

  40. 

  41. 	lp.phi = aasin(xy.y / C_y);
    42. 

  42. 	lp.lam = xy.x / (C_x * (1. + (c = cos(lp.phi))));
    43. 

  43. 	lp.phi = aasin((lp.phi + sin(lp.phi) * (c + 2.)) / C_p);
    44. 

  44. 	return (lp);
    45. 

  45. }
    46. 

  46. FREEUP; if (P) pj_dalloc(P); }
    47. 

  47. ENTRY0(eck4); P->es = 0.; P->inv = s_inverse; P->fwd = s_forward; ENDENTRY(P)
    48.