source: inundation/utilities/polygon.py @ 1906

#####################################
#POLYGON STUFF
#
#FIXME: All these should be put into new module polygon.py



def point_on_line(x, y, x0, y0, x1, y1):
    """Determine whether a point is on a line segment

    Input: x, y, x0, x0, x1, y1: where
        point is given by x, y
        line is given by (x0, y0) and (x1, y1)

    """

    from Numeric import array, dot, allclose
    from math import sqrt

    a = array([x - x0, y - y0])
    a_normal = array([a[1], -a[0]])

    b = array([x1 - x0, y1 - y0])

    if dot(a_normal, b) == 0:
        #Point is somewhere on the infinite extension of the line

        len_a = sqrt(sum(a**2))
        len_b = sqrt(sum(b**2))
        if dot(a, b) >= 0 and len_a <= len_b:
           return True
        else:
           return False
    else:
      return False



#These have been redefined to use separate_by_polygon which will
#put all inside indices in the first part of the indices array and
#outside indices in the last

def inside_polygon(points, polygon, closed = True, verbose = False):
    """See separate_points_by_polygon for documentation
    """

    from Numeric import array, Float, reshape

    if verbose: print 'Checking input to inside_polygon'
    try:
        points = ensure_numeric(points, Float)
    except:
        msg = 'Points could not be converted to Numeric array'
        raise msg

    try:
        polygon = ensure_numeric(polygon, Float)
    except:
        msg = 'Polygon could not be converted to Numeric array'
        raise msg



    if len(points.shape) == 1:
        one_point = True
        points = reshape(points, (1,2))
    else:
        one_point = False

    indices, count = separate_points_by_polygon(points, polygon,
                                                closed, verbose)

    if one_point:
        return count == 1
    else:
        return indices[:count]

def outside_polygon(points, polygon, closed = True, verbose = False):
    """See separate_points_by_polygon for documentation
    """

    from Numeric import array, Float, reshape

    if verbose: print 'Checking input to outside_polygon'
    try:
        points = ensure_numeric(points, Float)
    except:
        msg = 'Points could not be converted to Numeric array'
        raise msg

    try:
        polygon = ensure_numeric(polygon, Float)
    except:
        msg = 'Polygon could not be converted to Numeric array'
        raise msg



    if len(points.shape) == 1:
        one_point = True
        points = reshape(points, (1,2))
    else:
        one_point = False

    indices, count = separate_points_by_polygon(points, polygon,
                                                closed, verbose)

    if one_point:
        return count != 1
    else:
        return indices[count:][::-1]  #return reversed


def separate_points_by_polygon(points, polygon,
                               closed = True, verbose = False):
    """Determine whether points are inside or outside a polygon

    Input:
       points - Tuple of (x, y) coordinates, or list of tuples
       polygon - list of vertices of polygon
       closed - (optional) determine whether points on boundary should be
       regarded as belonging to the polygon (closed = True)
       or not (closed = False)

    Outputs:
       indices: array of same length as points with indices of points falling
       inside the polygon listed from the beginning and indices of points
       falling outside listed from the end.

       count: count of points falling inside the polygon

       The indices of points inside are obtained as indices[:count]
       The indices of points outside are obtained as indices[count:]


    Examples:
       U = [[0,0], [1,0], [1,1], [0,1]] #Unit square

       separate_points_by_polygon( [[0.5, 0.5], [1, -0.5], [0.3, 0.2]], U)
       will return the indices [0, 2, 1] and count == 2 as only the first
       and the last point are inside the unit square

    Remarks:
       The vertices may be listed clockwise or counterclockwise and
       the first point may optionally be repeated.
       Polygons do not need to be convex.
       Polygons can have holes in them and points inside a hole is
       regarded as being outside the polygon.

    Algorithm is based on work by Darel Finley,
    http://www.alienryderflex.com/polygon/

    """

    from Numeric import array, Float, reshape, Int, zeros


    #Input checks
    try:
        points = ensure_numeric(points, Float)
    except:
        msg = 'Points could not be converted to Numeric array'
        raise msg

    try:
        polygon = ensure_numeric(polygon, Float)
    except:
        msg = 'Polygon could not be converted to Numeric array'
        raise msg

    assert len(polygon.shape) == 2,\
       'Polygon array must be a 2d array of vertices'

    assert polygon.shape[1] == 2,\
       'Polygon array must have two columns'

    assert len(points.shape) == 2,\
       'Points array must be a 2d array'

    assert points.shape[1] == 2,\
       'Points array must have two columns'

    N = polygon.shape[0] #Number of vertices in polygon
    M = points.shape[0]  #Number of points

    px = polygon[:,0]
    py = polygon[:,1]

    #Used for an optimisation when points are far away from polygon
    minpx = min(px); maxpx = max(px)
    minpy = min(py); maxpy = max(py)


    #Begin main loop
    indices = zeros(M, Int)

    inside_index = 0    #Keep track of points inside
    outside_index = M-1 #Keep track of points outside (starting from end)

    for k in range(M):

        if verbose:
            if k %((M+10)/10)==0: print 'Doing %d of %d' %(k, M)

        #for each point
        x = points[k, 0]
        y = points[k, 1]

        inside = False

        if not x > maxpx or x < minpx or y > maxpy or y < minpy:
            #Check polygon
            for i in range(N):
                j = (i+1)%N

                #Check for case where point is contained in line segment
                if point_on_line(x, y, px[i], py[i], px[j], py[j]):
                    if closed:
                        inside = True
                    else:
                        inside = False
                    break
                else:
                    #Check if truly inside polygon
                    if py[i] < y and py[j] >= y or\
                       py[j] < y and py[i] >= y:
                        if px[i] + (y-py[i])/(py[j]-py[i])*(px[j]-px[i]) < x:
                            inside = not inside

        if inside:
            indices[inside_index] = k
            inside_index += 1
        else:
            indices[outside_index] = k
            outside_index -= 1

    return indices, inside_index


def separate_points_by_polygon_c(points, polygon,
                                 closed = True, verbose = False):
    """Determine whether points are inside or outside a polygon

    C-wrapper
    """

    from Numeric import array, Float, reshape, zeros, Int


    if verbose: print 'Checking input to separate_points_by_polygon'
    #Input checks
    try:
        points = ensure_numeric(points, Float)
    except:
        msg = 'Points could not be converted to Numeric array'
        raise msg

    #if verbose: print 'Checking input to separate_points_by_polygon 2'
    try:
        polygon = ensure_numeric(polygon, Float)
    except:
        msg = 'Polygon could not be converted to Numeric array'
        raise msg

    if verbose: print 'check'

    assert len(polygon.shape) == 2,\
       'Polygon array must be a 2d array of vertices'

    assert polygon.shape[1] == 2,\
       'Polygon array must have two columns'

    assert len(points.shape) == 2,\
       'Points array must be a 2d array'

    assert points.shape[1] == 2,\
       'Points array must have two columns'

    N = polygon.shape[0] #Number of vertices in polygon
    M = points.shape[0]  #Number of points

    from util_ext import separate_points_by_polygon

    if verbose: print 'Allocating array for indices'

    indices = zeros( M, Int )

    if verbose: print 'Calling C-version of inside poly'
    count = separate_points_by_polygon(points, polygon, indices,
                                       int(closed), int(verbose))

    return indices, count



class Polygon_function:
    """Create callable object f: x,y -> z, where a,y,z are vectors and
    where f will return different values depending on whether x,y belongs
    to specified polygons.

    To instantiate:

       Polygon_function(polygons)

    where polygons is a list of tuples of the form

      [ (P0, v0), (P1, v1), ...]

      with Pi being lists of vertices defining polygons and vi either
      constants or functions of x,y to be applied to points with the polygon.

    The function takes an optional argument, default which is the value
    (or function) to used for points not belonging to any polygon.
    For example:

       Polygon_function(polygons, default = 0.03)

    If omitted the default value will be 0.0

    Note: If two polygons overlap, the one last in the list takes precedence

    FIXME? : Currently, coordinates specified here are assumed to be relative to the origin (georeference) used by domain. This function is more general than domain so perhaps it'd be an idea to allow the optional argument georeference???

    """

    def __init__(self, regions, default = 0.0):

        try:
            len(regions)
        except:
            msg = 'Polygon_function takes a list of pairs (polygon, value). Got %s' %polygons
            raise msg


        T = regions[0]
        try:
            a = len(T)
        except:
            msg = 'Polygon_function takes a list of pairs (polygon, value). Got %s' %polygons
            raise msg

        assert a == 2, 'Must have two component each: %s' %T

        self.regions = regions
        self.default = default


    def __call__(self, x, y):
        from util import inside_polygon
        from Numeric import ones, Float, concatenate, array, reshape, choose

        x = array(x).astype(Float)
        y = array(y).astype(Float)

        N = len(x)
        assert len(y) == N

        points = concatenate( (reshape(x, (N, 1)),
                               reshape(y, (N, 1))), axis=1 )

        if callable(self.default):
            z = self.default(x,y)
        else:
            z = ones(N, Float) * self.default

        for polygon, value in self.regions:
            indices = inside_polygon(points, polygon)

            #FIXME: This needs to be vectorised
            if callable(value):
                for i in indices:
                    xx = array([x[i]])
                    yy = array([y[i]])
                    z[i] = value(xx, yy)[0]
            else:
                for i in indices:
                    z[i] = value

        return z

def read_polygon(filename):
    """Read points assumed to form a polygon
       There must be exactly two numbers in each line
    """

    #Get polygon
    fid = open(filename)
    lines = fid.readlines()
    fid.close()
    polygon = []
    for line in lines:
        fields = line.split(',')
        polygon.append( [float(fields[0]), float(fields[1])] )

    return polygon

def populate_polygon(polygon, number_of_points, seed = None, exclude = None):
    """Populate given polygon with uniformly distributed points.

    Input:
       polygon - list of vertices of polygon
       number_of_points - (optional) number of points
       seed - seed for random number generator (default=None)
       exclude - list of polygons (inside main polygon) from where points should be excluded 

    Output:
       points - list of points inside polygon

    Examples:
       populate_polygon( [[0,0], [1,0], [1,1], [0,1]], 5 )
       will return five randomly selected points inside the unit square
    """

    from random import uniform, seed

    seed(seed)

    points = []

    #Find outer extent of polygon
    max_x = min_x = polygon[0][0]
    max_y = min_y = polygon[0][1]
    for point in polygon[1:]:
        x = point[0]
        if x > max_x: max_x = x
        if x < min_x: min_x = x
        y = point[1]
        if y > max_y: max_y = y
        if y < min_y: min_y = y


    while len(points) < number_of_points:
        x = uniform(min_x, max_x)
        y = uniform(min_y, max_y)

        append = False
        if inside_polygon( [x,y], polygon ):

            append = True
            
            #Check exclusions
            if exclude is not None:
                for ex_poly in exclude:
                    if inside_polygon( [x,y], ex_poly ):
                        append = False
                        
                    
        if append is True:                
            points.append([x,y])                

    return points





##############################################
#Initialise module

import compile
if compile.can_use_C_extension('polygon_ext.c'):
    from polygon_ext import point_on_line
    separate_points_by_polygon = separate_points_by_polygon_c


if __name__ == "__main__":
    pass