def extract_curve(self, u1, v1, u2, v2, basis_shape=None):
"""
Extract a trimmed curve within the reference surface between the
parameters.
:param float u1: First u-parameter.
:param float v1: First v-parameter.
:param float u2: Second u-parameter.
:param float v2: Second v-parameter.
:param basis_shape: The shape that will be used to intersect with
the reference shape. If not provided a plane will be
created using the *extract_plane()* method. The parameters
should create points that are on or very near the intersection
between these two shapes. If they are not they will be projected to
the intersection which could yield unanticipated results.
:type basis_shape: afem.geometry.entities.Surface or
afem.topology.entities.Shape
:return: The curve.
:rtype: afem.geometry.entities.TrimmedCurve
:raise RuntimeError: If method fails.
"""
p1 = self.sref.eval(u1, v1)
p2 = self.sref.eval(u2, v2)
if basis_shape is None:
basis_shape = self.extract_plane(u1, v1, u2, v2)
basis_shape = Shape.to_shape(basis_shape)
bop = IntersectShapes(basis_shape, self.sref_shape, approximate=True)
shape = bop.shape
edges = shape.edges
builder = WiresByConnectedEdges(edges)
if builder.nwires == 0:
msg = 'Failed to extract any curves.'
raise RuntimeError(msg)
if builder.nwires == 1:
wire = builder.wires[0]
else:
dist = DistancePointToShapes(p1, builder.wires)
wire = dist.nearest_shape
crv = wire.curve
proj = ProjectPointToCurve(p1, crv)
if not proj.success:
msg = 'Failed to project point to reference curve.'
raise RuntimeError(msg)
u1c = proj.nearest_param
proj = ProjectPointToCurve(p2, crv)
if not proj.success:
msg = 'Failed to project point to reference curve.'
raise RuntimeError(msg)
u2c = proj.nearest_param
if u1c > u2c:
crv.reverse()
u1c, u2c = crv.reversed_u(u1c), crv.reversed_u(u2c)
return TrimmedCurve.by_parameters(crv, u1c, u2c)