Function gmtplot_geo_vector_greatcircle

src/gmt_plot.c:5397–5618

}

GMT_LOCAL unsigned int gmtplot_geo_vector_greatcircle (struct GMT_CTRL *GMT, double lon0, double lat0, double azimuth, double length, struct GMT_PEN *ppen, struct GMT_SYMBOL *S) {
	/* Draws a great-circle vector with our without heads, etc. There are some complications to consider:
	 * When there are no heads it is simple.  If +n is on we may shrink the line thickness.
	 * With heads there are these cases:
	 * Head length is longer than 90% of the vector length.  We then skip the head and return 1
	 * +n<norm> is in effect.  We shrink vector pen and head length.  Still, the shrunk head
	 * may be longer than 90% of the vector length.  We then shrink head (not pen) further and return 2
	*/

	uint64_t n1, n2, n, add;
	int heads, side[2], outline = 0;
	unsigned int warn = 0;
	size_t n_alloc;
	bool perspective, pure;
	double tlon, tlat, mlon, mlat, P[3], Ax[3], Bx[3], h_length_limit;
	double dr[2] = {0.0, 0.0}, az[2] = {0.0, 0.0}, oaz[2] = {0.0, 0.0}, off[2] = {0.0, 0.0};
	double da = 0.0, dshift[2] = {0.0, 0.0}, s = 1.0, s1 = 1.0, s2 = 1.0, olon[2], olat[2], head_length, arc_width, rot, scl[2];
	double *xp = NULL, *yp = NULL, *xp2 = NULL, *yp2 = NULL;
	double *rgb = S->v.fill.rgb;
	struct GMT_CIRCLE C;

	/* We must determine points A and B, whose great-circle connector is the arc we seek to draw */
	gmtplot_gcircle_sub (GMT, lon0, lat0, azimuth, length, S, &C);
	perspective = gmt_M_is_perspective (GMT);

	/* Here we have the endpoints A and B of the great (or small) circle arc */

	/* If shrink-option (+n) is active we may have to scale down head attributes and pen width */
	pure = (S->v.v_norm == -1.0f);	/* True if no shrinking has been specified */
	heads = PSL_vec_head (S->v.status);	/* Return head selection as 0-3 */
	h_length_limit = C.r0;	/* Max length of arrow in degrees to ensure the stem is still showing */
	if (heads == 3) h_length_limit *= 0.5;		/* Split this length between the two heads */
	if (heads && !pure) {	/* Need to determine head length in degrees */
		double max_length;
		az[0]  = gmt_az_backaz (GMT, C.lon[0], C.lat[0], C.lon[1], C.lat[1], false);	/* Compute the azimuth from A to B at A along great circle */
		scl[0] = (perspective) ? S->v.scale : gmtplot_get_local_scale (GMT, C.lon[0], C.lat[0], 0.001 * C.r, az[0]);	/* Get local deg/inch scale at A in az[0] direction */
		dr[0] = scl[0] * S->size_x;	/* This is arrow head length in degrees, approximately */
		az[1]  = gmt_az_backaz (GMT, C.lon[1], C.lat[1], C.lon[0], C.lat[0], false);	/* Compute the azimuth from B to A at B along great circle */
		scl[1] = (perspective) ? S->v.scale : gmtplot_get_local_scale (GMT, C.lon[1], C.lat[1], 0.01 * C.r, az[1]);	/* Get local deg/inch scale */
		dr[1] = scl[1] * S->size_x;	/* This is arrow head length in degrees, approximately, adjusted for ~pen thickness to ensure no gap between head and line */
		max_length = MAX (dr[0], dr[1]);
		if (max_length > h_length_limit) {
			s2 = h_length_limit / max_length;
			if (s2 < S->v.v_norm_limit) s2 = S->v.v_norm_limit;
			warn = 2;
		}
	}

	/* Might have to shrink things */

	s1 = gmt_get_vector_shrinking (GMT, &(S->v), S->v.value, C.r0); /* Vector attribute shrinking factor or 1 */

	if (s1 < s2) {	/* Pick the smallest scale required for head shrinking */
		s = s1;
		warn = 0;	/* When requesting +n there is no warning unless s2 is the smaller scale */
	}
	else
		s = s2;