Using Evaluators

NURBS-Python (geomdl) 4.x series come with a nice feature called Evaluators. In simple words, an Evaluator allows users to change the evaluation algorithms, such as finding curve & surface points, taking derivatives, inserting knots and similar. You may also call it more technically as an evaluation strategy.

The following code example illustrates switching between alternative derivative algorithms of the Curve class which are previously implemented as derivatives() and derivatives2().

from geomdl import BSpline
from geomdl import utilities
from geomdl import evaluators

# Create a B-Spline curve instance
curve = BSpline.Curve()

# Set degree
curve.degree = 3

# Set control points
curve.ctrlpts = [[5.0, 5.0], [10.0, 20.0], [20.0, 35.0], 
                 [35.0, 35.0], [45.0, 20.0], [50.0, 5.0]]

# Auto-generate knot vector
curve.knotvector = utilities.generate_knot_vector(curve.degree, len(curve.ctrlpts))

# Evaluate derivatives at u = 0.6
ders1 = curve.derivatives(0.6, 2)

# Change evaluator
curve.evaluator = evaluators.CurveEvaluator2()

# Evaluate derivatives at u = 0.6 using the new evaluator
ders2 = curve.derivatives(0.6, 2)