True if polygon vertices are in clockwise order
tf = ispolycw(x,y)
tf = ispolycw(x,y) returns true if the polygonal
contour vertices represented by x and y are
ordered in the clockwise direction. x and y are
Cartesian vectors with the same number of elements.
Alternatively, x and y can
contain multiple contours, either in NaN-separated
vector form or in cell array form. In that case, ispolycw returns
a logical array containing one true or false value per contour.
ispolycw always returns true for polygonal
contours containing two or fewer vertices.
Vertex ordering is not well defined for self-intersecting polygonal contours. For such
contours, ispolycw returns a result based on the order or vertices
immediately before and after the left-most of the lowest vertices. In other words, of
the vertices with the lowest y value, find the vertex with the lowest
x value. For a few special cases of self-intersecting contours,
the vertex ordering cannot be determined using only the left-most of the lowest
vertices; for these cases, ispolycw uses a signed area test to
determine the ordering.
x and y may be any numeric
class.
Orientation of a square:
x = [0 1 1 0 0]; y = [0 0 1 1 0]; ispolycw(x, y) % Returns 0 ispolycw(fliplr(x), fliplr(y)) % Returns 1
You can use ispolycw for geographic coordinates if the polygon
does not cross the Antimeridian or contain a pole. A polygon contains a pole if the
longitude data spans 360 degrees. To use ispolycw with geographic
coordinates, specify the longitude vector as x and the latitude
vector as y.