source: inundation/ga/storm_surge/pyvolution/mesh_factory.py @ 1093

"""Library of standard meshes and facilities for reading various
mesh file formats
"""


def rectangular(m, n, len1=1.0, len2=1.0, origin = (0.0, 0.0)):

    """Setup a rectangular grid of triangles
    with m+1 by n+1 grid points
    and side lengths len1, len2. If side lengths are omitted
    the mesh defaults to the unit square.
    
    len1: x direction (left to right)
    len2: y direction (bottom to top)

    Return to lists: points and elements suitable for creating a Mesh or
    FVMesh object, e.g. Mesh(points, elements) 
    """

    from config import epsilon
    
    #E = m*n*2        #Number of triangular elements
    #P = (m+1)*(n+1)  #Number of initial vertices

    delta1 = float(len1)/m
    delta2 = float(len2)/n    

    #Dictionary of vertex objects
    vertices = {}
    points = []

    for i in range(m+1):
        for j in range(n+1):
            vertices[i,j] = len(points)
            points.append([i*delta1 + origin[0], j*delta2 + origin[1]])



    #Construct 2 triangles per rectangular element and assign tags to boundary
    elements = []
    boundary = {}
    for i in range(m):
        for j in range(n):
            v1 = vertices[i,j+1]
            v2 = vertices[i,j]            
            v3 = vertices[i+1,j+1]            
            v4 = vertices[i+1,j]            

            #Update boundary dictionary and create elements
            if i == m-1:
                boundary[(len(elements), 2)] = 'right'
            if j == 0:
                boundary[(len(elements), 1)] = 'bottom'                
            elements.append([v4,v3,v2]) #Lower element

            if i == 0:
                boundary[(len(elements), 2)] = 'left'
            if j == n-1:
                boundary[(len(elements), 1)] = 'top' 
            elements.append([v1,v2,v3]) #Upper element   

    return points, elements, boundary       


def oblique(m, n, lenx = 1.0, leny = 1.0, theta = 8.95, origin = (0.0, 0.0)):
    """Setup a oblique grid of triangles
    with m segments in the x-direction and n segments in the y-direction

    """

    from Numeric import array
    import math

    from config import epsilon


    deltax = lenx/float(m)
    deltay = leny/float(n)
    a = 0.75*lenx*math.tan(theta/180.*math.pi)
    x1 = lenx
    y1 = 0
    x2 = lenx
    y2 = leny
    x3 = 0.25*lenx
    y3 = leny
    x4 = x3
    y4 = 0
    a2 = a/(x1-x4)
    a1 = -a2*x4
    a4 = ((a1 + a2*x3)/y3-(a1 + a2*x2)/y2)/(x2-x3)
    a3 = 1. - (a1 + a2*x3)/y3 - a4*x3

    # Dictionary of vertex objects
    vertices = {}
    points = []

    for i in range(m+1):
        x = deltax*i
        for j in range(n+1):     
            y = deltay*j
            if x > 0.25*lenx:
                y = a1 + a2*x + a3*y + a4*x*y
                
            vertices[i,j] = len(points)
            points.append([x + origin[0], y + origin[1]])

    # Construct 2 triangles per element        
    elements = []
    boundary = {}
    for i in range(m):
        for j in range(n):
            v1 = vertices[i,j+1]
            v2 = vertices[i,j]            
            v3 = vertices[i+1,j+1]            
            v4 = vertices[i+1,j]
            
            #Update boundary dictionary and create elements
            if i == m-1:
                boundary[(len(elements), 2)] = 'right'
            if j == 0:
                boundary[(len(elements), 1)] = 'bottom'                
            elements.append([v4,v3,v2]) #Lower

            if i == 0:
                boundary[(len(elements), 2)] = 'left'
            if j == n-1:
                boundary[(len(elements), 1)] = 'top' 
             
            elements.append([v1,v2,v3]) #Upper

    return points, elements, boundary       


def circular(m, n, radius=1.0, center = (0.0, 0.0)):
    """Setup a circular grid of triangles with m concentric circles and
    with n radial segments. If radius is are omitted the mesh defaults to
    the unit circle radius.
 
    radius: radius of circle
    
    #FIXME: The triangles become degenerate for large values of m or n.
    """


    
    from math import pi, cos, sin

    radius = float(radius) #Ensure floating point format

    #Dictionary of vertex objects and list of points
    vertices = {}
    points = [[0.0, 0.0]] #Center point
    vertices[0, 0] = 0
    
    for i in range(n):
        theta = 2*i*pi/n
        x = cos(theta)
        y = sin(theta)
        for j in range(1,m+1):
            delta = j*radius/m
            vertices[i,j] = len(points)
            points.append([delta*x, delta*y])

    #Construct 2 triangles per element        
    elements = []
    for i in range(n):
        for j in range(1,m):

            i1 = (i + 1) % n  #Wrap around  
            
            v1 = vertices[i,j+1]
            v2 = vertices[i,j]            
            v3 = vertices[i1,j+1]            
            v4 = vertices[i1,j]

            elements.append([v4,v2,v3]) #Lower                
            elements.append([v1,v3,v2]) #Upper


    #Do the center
    v1 = vertices[0,0]
    for i in range(n):
        i1 = (i + 1) % n  #Wrap around          
        v2 = vertices[i,1]
        v3 = vertices[i1,1]

        elements.append([v1,v2,v3]) #center
         
    return points, elements


def from_polyfile(name):
    """Read mesh from .poly file, an obj like file format
    listing first vertex coordinates and then connectivity
    """

    from util import anglediff
    from math import pi
    import os.path
    root, ext = os.path.splitext(name)

    if ext == 'poly':
        filename = name
    else:
        filename = name + '.poly'

    
    fid = open(filename)

    points = []    #x, y
    values = []    #z
    ##vertex_values = []    #Repeated z    
    triangles = [] #v0, v1, v2
    
    lines = fid.readlines()

    keyword = lines[0].strip()
    msg = 'First line in .poly file must contain the keyword: POINTS'
    assert keyword == 'POINTS', msg

    offending = 0
    i = 1
    while keyword == 'POINTS':
        line = lines[i].strip()
        i += 1

        if line == 'POLYS':
            keyword = line
            break

        fields = line.split(':')
        assert int(fields[0]) == i-1, 'Point indices not consecutive'

        #Split the three floats
        xyz = fields[1].split()

        x = float(xyz[0])
        y = float(xyz[1])
        z = float(xyz[2])        

        points.append([x, y])
        values.append(z)
        

    k = i    
    while keyword == 'POLYS':
        line = lines[i].strip()
        i += 1

        if line == 'END':
            keyword = line
            break
        

        fields = line.split(':')
        assert int(fields[0]) == i-k, 'Poly indices not consecutive'

        #Split the three indices
        vvv = fields[1].split()

        i0 = int(vvv[0])-1
        i1 = int(vvv[1])-1
        i2 = int(vvv[2])-1

        #Check for and exclude degenerate areas
        x0 = points[i0][0]
        y0 = points[i0][1]
        x1 = points[i1][0]
        y1 = points[i1][1]
        x2 = points[i2][0]
        y2 = points[i2][1]                

        area = abs((x1*y0-x0*y1)+(x2*y1-x1*y2)+(x0*y2-x2*y0))/2
        if area > 0:

            #Ensure that points are arranged in counter clock-wise order
            v0 = [x1-x0, y1-y0]
            v1 = [x2-x1, y2-y1]
            v2 = [x0-x2, y0-y2]

            a0 = anglediff(v1, v0)
            a1 = anglediff(v2, v1)
            a2 = anglediff(v0, v2)        

            
            if a0 < pi and a1 < pi and a2 < pi:
                #all is well
                j0 = i0
                j1 = i1
                j2 = i2
            else:
                #Swap two vertices
                j0 = i1
                j1 = i0
                j2 = i2
                
            triangles.append([j0, j1, j2])
            ##vertex_values.append([values[j0], values[j1], values[j2]])
        else:
            offending +=1 

    print 'Removed %d offending triangles out of %d' %(offending, len(lines))
    return points, triangles, values



def strang_mesh(filename):
    """Read Strang generated mesh.
    """

    from math import pi
    from util import anglediff
    
    
    fid = open(filename)
    points = []    # List of x, y coordinates
    triangles = [] # List of vertex ids as listed in the file
    
    for line in fid.readlines():
        fields = line.split()
        if len(fields) == 2:
            # we are reading vertex coordinates
            points.append([float(fields[0]), float(fields[1])])
        elif len(fields) == 3:
            # we are reading triangle point id's (format ae+b)
            triangles.append([int(float(fields[0]))-1,
                              int(float(fields[1]))-1,
                              int(float(fields[2]))-1])
        else:
            raise 'wrong format in ' + filename

    elements = [] #Final list of elements

    for t in triangles:
        #Get vertex coordinates
        v0 = t[0]
        v1 = t[1]
        v2 = t[2]
        
        x0 = points[v0][0]
        y0 = points[v0][1]
        x1 = points[v1][0]
        y1 = points[v1][1]
        x2 = points[v2][0]
        y2 = points[v2][1]                

        #Check that points are arranged in counter clock-wise order
        vec0 = [x1-x0, y1-y0]
        vec1 = [x2-x1, y2-y1]
        vec2 = [x0-x2, y0-y2]

        a0 = anglediff(vec1, vec0)
        a1 = anglediff(vec2, vec1)
        a2 = anglediff(vec0, vec2)        

        if a0 < pi and a1 < pi and a2 < pi:
            elements.append([v0, v1, v2])
        else:
            elements.append([v0, v2, v1])       

    return points, elements                             

# #Map from edge number to indices of associated vertices
# edge_map = ((1,2), (0,2), (0,1))