def surfpt(self, u=-1, v=-1, check_vars=True, get_ctrlpts=False):
""" Evaluates the NURBS surface at the given (u,v) parameters.
:param u: parameter in the U direction
:type u: float
:param v: parameter in the V direction
:type v: float
:param check_vars: flag to disable variable checking (only for internal eval functions)
:type check_vars: bool
:param get_ctrlpts: flag to add a list of control points associated with the surface evaluation to the return value
:param get_ctrlpts: bool
:return: evaluated surface point at the given knot values
:rtype: list
"""
if check_vars:
# Check all parameters are set before the surface evaluation
self._check_variables()
# Check u and v parameters are correct
utils.check_uv(u, v)
# Initialize an empty list which will contain the list of associated control points
ctrlpts = []
# Algorithm A4.3
span_v = utils.find_span(self._degree_v, tuple(self._knot_vector_v),
self._control_points_size_v, v)
basis_v = utils.basis_functions(self._degree_v,
tuple(self._knot_vector_v), span_v, v)
span_u = utils.find_span(self._degree_u, tuple(self._knot_vector_u),
self._control_points_size_u, u)
basis_u = utils.basis_functions(self._degree_u,
tuple(self._knot_vector_u), span_u, u)
idx_u = span_u - self._degree_u
sptw = [0.0 for x in range(self._dimension)]
for l in range(0, self._degree_v + 1):
temp = [0.0 for x in range(self._dimension)]
idx_v = span_v - self._degree_v + l
for k in range(0, self._degree_u + 1):
temp[:] = [
tmp + (basis_u[k] * cp) for tmp, cp in zip(
temp, self._control_points2D[idx_u + k][idx_v])
]
if get_ctrlpts:
ctrlpts.append(self._control_points2D[idx_u + k][idx_v])
sptw[:] = [
ptw + (basis_v[l] * tmp) for ptw, tmp in zip(sptw, temp)
]
# Divide by weight
spt = []
for idx in range(self._dimension - 1):
spt.append(float(sptw[idx] / sptw[-1]))
if get_ctrlpts:
return spt, ctrlpts
return spt
def test_check_uv4():
with pytest.raises(ValueError):
v = 2
u = 0.1
utilities.check_uv(u, v)
def test_check_uv2():
with pytest.raises(ValueError):
u = 2
v = 0.1
utilities.check_uv(u, v)