Function gmtplot_gcircle_sub

src/gmt_plot.c:4929–4982

}

GMT_LOCAL void gmtplot_gcircle_sub (struct GMT_CTRL *GMT, double lon0, double lat0, double azimuth, double length, struct GMT_SYMBOL *S, struct GMT_CIRCLE *C) {
	/* We must determine points A and B, whose great-circle connector is the arc we seek to draw */

	int justify = PSL_vec_justify (S->v.status);	/* Return justification as 0-3 */
	double x, y;
	gmt_M_memset (C, 1, struct GMT_CIRCLE);	/* Set all to zero */

	if (S->v.status & PSL_VEC_JUST_S) { /* Was given coordinates of A and B */
		justify = 3;
	}
	switch (justify) {	/* A and B depends on chosen justification */
		case 0: /* Was given coordinates of A; determine B */
			C->lon[0] = lon0;	C->lat[0] = lat0;
			gmt_geo_to_cart (GMT, C->lat[0], C->lon[0], C->A, true);
			C->r0 = C->r = length / GMT->current.proj.DIST_KM_PR_DEG;	/* Arch length in spherical degrees */
			if (C->r > 180.0) {C->longway = true; C->r -= 180.0;}	/* Temporarily adjust if arcs > 180 degrees are chosen */
			gmtlib_get_point_from_r_az (GMT, C->lon[0], C->lat[0], C->r, azimuth, &C->lon[1], &C->lat[1]);
			if (C->longway) C->lon[1] += 180.0, C->lat[1] = -C->lat[1];	/* Undo adjustment */
			gmt_geo_to_cart (GMT, C->lat[1], C->lon[1], C->B, true);	/* Get B */
			break;
		case 1: /* Was given coordinates of halfway point; determine A and B */
			C->r0 = C->r = length / GMT->current.proj.DIST_KM_PR_DEG;	/* Arch length in spherical degrees */
			if (C->r > 180.0) C->longway = true;	/* Temporarily adjust if arcs > 180 degrees are chosen */
			gmtlib_get_point_from_r_az (GMT, lon0, lat0, 0.5*C->r, azimuth, &C->lon[1], &C->lat[1]);
			gmt_geo_to_cart (GMT, C->lat[1], C->lon[1], C->B, true);	/* Get B */
			gmtlib_get_point_from_r_az (GMT, lon0, lat0, 0.5*C->r, azimuth+180.0, &x, &y);
			C->lon[0] = x;	C->lat[0] = y;	/* Replace the original A point */
			gmt_geo_to_cart (GMT, C->lat[0], C->lon[0], C->A, true);	/* Get A */
			break;
		case 2: /* Was given coordinates of B point; determine A */
			C->lon[0] = lon0;	C->lat[0] = lat0;
			gmt_geo_to_cart (GMT, C->lat[0], C->lon[0], C->B, true);
			C->r0 = C->r = length / GMT->current.proj.DIST_KM_PR_DEG;	/* Arch length in spherical degrees */
			if (C->r > 180.0) {C->longway = true; C->r -= 180.0;}	/* Temporarily adjust if arcs > 180 degrees are chosen */
			gmtlib_get_point_from_r_az (GMT, C->lon[0], C->lat[0], C->r, azimuth+180.0, &C->lon[1], &C->lat[1]);
			if (C->longway) C->lon[1] += 180.0, C->lat[1] = -C->lat[1];	/* Undo adjustment */
			gmt_geo_to_cart (GMT, C->lat[1], C->lon[1], C->A, true);	/* Get A */
			gmt_M_double_swap (C->lon[0], C->lon[1]);	gmt_M_double_swap (C->lat[0], C->lat[1]);	/* Now A is first and B is second */
			break;
		case 3: /* Was given coordinates of B instead of azimuth and length; can never be longway */
			C->lon[0] = lon0;	C->lat[0] = lat0;
			C->lat[1] = length;	C->lon[1] = azimuth;
			gmt_geo_to_cart (GMT, C->lat[0], C->lon[0], C->A, true);	/* Get A */
			gmt_geo_to_cart (GMT, C->lat[1], C->lon[1], C->B, true);	/* Get B */
			C->r0 = C->r = d_acosd (gmt_dot3v (GMT, C->A, C->B));		/* Arc length in degrees */
			break;
	}
	gmt_cross3v (GMT, C->A, C->B, C->P);	/* Rotation pole */
	gmt_normalize3v (GMT, C->P);		/* Rotation pole unit vector */

	if (C->longway) {	/* Want to go the long way */
		C->P[0] = -C->P[0], C->P[1] = -C->P[1], C->P[2] = -C->P[2];
	}
}

GMT_LOCAL void gmtplot_scircle_sub (struct GMT_CTRL *GMT, double lon0, double lat0, double angle_1, double angle_2, struct GMT_SYMBOL *S, struct GMT_CIRCLE *C) {
	/* We must determine points A and B, whose small-circle connector about pole P is the arc we seek to draw */