Function inside 

pub unsafe extern "C" fn inside(
    p: *const c_double,
    lv: *const c_int,
    xv: *const c_double,
    yv: *const c_double,
    zv: *const c_double,
    nv: *const c_int,
    listv: *const c_int,
    ier: *mut c_int,
) -> bool

Determines if a point is inside a polygonal region.

This function locates a point p relative to a polygonal region r on the surface of the unit sphere, returning inside = true if and only if p is contained in r. r is defined by a cyclically ordered sequence of vertices which form a positively-oriented simple closed curve. Adjacent vertices need not be distinct but the curve must not be self-intersecting. Also, while polygon edges are by definition restricted to a single hemisphere, r is not so restricted. Its interior is the region to the left as the vertices are traversed in order.

The algorithm consists of selecting a point q in r and then finding all points at which the great circle defined by p and q intersects the boundary of r. p lies inside r if and only if there is an even number of intersection points between q and p. q is taken to be a point immediately to the left of a directed boundary edge – the first one that results in no consistency-check failures.

If p is close to the polygon boundary, the problem is ill-conditioned and the decision may be incorrect. Also, an incorrect decision may result from a poor choice of q (if, for example, a boundary edge lies on the great circle defined by p and q). A more reliable result could be obtained by a sequence of calls to inside with the vertices cyclically permuted before each call (to alter the choice of q).

Arguments

• p[3] - Input. The coordinates of the point (unit vector) to be located.
• lv - Input. The length of the arrays xv, yv, and zv.
• xv[lv], yv[lv], zv[lv] - Input. The coordinates of unit vectors (points on the unit sphere).
• nv - Input. The number of vertices in the polygon. 3 <= nv <= lv.
• listv[nv] - Input. The indexes (for xv, yv, and zv) of a cyclically-ordered (and CCW-ordered) sequence of vertices that define r. The last vertex (indexed by listv[nv]) is followed by the first (indexed by listv[1]). listv entries must be in the range 1 to lv.
• ier - Output. Error indicator:
  • 0, if no errors were encountered.
  • 1, if lv or nv is outside its valid range.
  • 2, if a listv entry is outside its valid range.
  • 3, if the polygon boundary was found to be self-intersecting. This error will not necessarily be detected.
  • 4, if every choice of q (one for each boundary edge) led to failure of some internal consistency check. The most likely cause of this error is invalid input: p = (0, 0, 0), a null or self-intersecting polygon, etc.

Returns

True if and only if p lies inside r unless ier != 0, in which case the value is not altered.