Let splipy.utils.refinement take SplineModel as input

In particular https://github.com/sintefmath/Splipy/blob/f7bf4ef8e2a15433ec9ac16498b2275cc44e265f/splipy/utils/refinement.py#L14 should accept as input argument obj a SplineModel. This should take advantage of neighbourhood information to propagate refinement across the domain.

In particular, the following script:

from splipy import *
from splipy.io import G2
from splipy.utils import refinement
import splipy.curve_factory as cf
import splipy.surface_factory as sf
import numpy as np
from numpy import sin, cos, arctan2, pi, sqrt, tan

# units in mm
R = 3      # radius
α = pi/6   # inlet angle
l1 = 20    # counterflow length (left side)
l2 = 10    # directedflow length (right side)
l3 = 10    # length before circular arc
w  =  4    # channel width

# first patch
patches = [Surface()*[l3, w]]
patches[-1][0,-1] = [-w/2/sin(α),w]

# compute the circle-channel intersection point(s)
b = -2*R*sin(α)-2*l3*cos(α)
c = l3**2
t1 = (-b+sqrt(b**2-4*c))/2
x1 =  t1*cos(α)
y1 = -t1*sin(α)
crv1 = cf.circle_segment_from_three_points([l3,0], [l3+R,-R], [x1,y1])
b = -2*R*sin(α)-2*l3*cos(α)
c = l3**2 - 2*R*w - w**2
t2 = (-b+sqrt(b**2-4*c))/2
x2 =  t2*cos(α)
y2 = -t2*sin(α)
crv2 = cf.circle_segment_from_three_points([l3,w], [l3+R+w,-R], [x2,y2])
# crv0 = cf.circle(center=[l3,-R], r=R) # debug help curve

patches.append(sf.edge_curves(crv1,crv2))

crv3 = cf.line([ 0,0],        t1*          np.array([cos(α), -sin(α)]))
crv4 = cf.line([-w/sin(α),0],(t1+w*cos(α))*np.array([cos(α), -sin(α)]), relative=True)
patches.append(sf.edge_curves(crv3,crv4))

crv3 = cf.line([x1,y1],         (t2-t1)*np.array([cos(α), -sin(α)]), relative=True)
crv4 = cf.line(patches[-1][-1], patches[1][-1][:2] + w*np.array([-sin(α), -cos(α)]))
patches.append(sf.edge_curves(crv3,crv4))

crv3 = cf.line([ 0,0], [-w/2/sin(α),w])
crv4 = cf.line([-w/sin(α),0], -w/sin(α)*np.array([cos(α), -sin(α)]), relative=True)
patches.append(sf.edge_curves(crv3,crv4))

crv3 = patches[-1].edges()[-1]
crv4 = cf.line([-l1,0], [-l1,w])
patches.append(sf.edge_curves(crv3,crv4))

crv3 = patches[3].edges()[1]
crv4 = crv3 + l2*np.array([cos(α), -sin(α)])
patches.append(sf.edge_curves(crv3,crv4))

# make all patches compatible
for p in patches:
  p.force_rational()
  dp = np.array([3,3]) - p.order()
  p.set_order(3,3)

with G2("multipatch.g2") as f:
    f.write(patches)

Which is producing the following 6-patch geometry

Screenshot from 2020-01-24 13-57-37

Should after calling

refinement.edge_refine(patches[0], S=3, direction='v', n=15)
refinement.edge_refine(patches[-1], S=3, direction='u', n=15)

Produce the following refinement Screenshot from 2020-01-24 13-58-20

SINTEF / Splipy

Let splipy.utils.refinement take SplineModel as input #107