Curvature Calculation Inaccurate for B-Spline Curves in DiffGeomCurve Class

[stp34650]

Description:

The current implementation of the curvature function in the DiffGeomCurve class from OCC.Utils.edge_py appears to provide inaccurate results when applied to B-spline curves. While the function successfully calculates curvature for circular edges, it consistently returns a value of 0 for B-spline curves, indicating inaccurate behavior.

Steps to Reproduce:

1. Obtain the attached TXT file (sin_curve.txt) containing a B-spline representation of a sine curve.
2. Change the file extension from .txt to .step.
3. Load the STEP file using pythonocc.
4. Obtain the curvature of the B-spline curve using the curvature function from the DiffGeomCurve class.

Expected Behavior:

The curvature function should accurately compute the curvature of B-spline curves, providing meaningful non-zero values consistent with the curvature of the curve at various points.

Actual Behavior:

The curvature function consistently returns 0 when applied to B-spline curves, while it correctly computes curvature for circular edges. This discrepancy indicates inaccurate behavior specific to B-spline curves.

Code Snippet:

from OCC.Core.TopExp import TopExp_Explorer
from OCC.Core.TopAbs import TopAbs_EDGE
from OCC.Core.GCPnts import GCPnts_UniformAbscissa
from OCC.Core.BRepAdaptor import BRepAdaptor_Curve
from OCC.Core.TDocStd import TDocStd_Document
from OCC.Core.XCAFDoc import XCAFDoc_DocumentTool
from OCC.Core.STEPCAFControl import STEPCAFControl_Reader
from OCC.Core.IFSelect import IFSelect_RetDone
from OCC.Core.TDF import TDF_LabelSequence

from OCCUtils.edge import Edge


doc = TDocStd_Document("pythonocc-doc")
shape_tool = XCAFDoc_DocumentTool.ShapeTool(doc.Main())

step_reader = STEPCAFControl_Reader()
step_reader.SetNameMode(True)

status = step_reader.ReadFile("sin_curve.step")
if status != IFSelect_RetDone:
    raise IOError("Failed to read STEP file")

step_reader.Transfer(doc)
labels = TDF_LabelSequence()
shape_tool.GetFreeShapes(labels)

shape = shape_tool.GetShape(labels.Value(1))

explorer = TopExp_Explorer(shape, TopAbs_EDGE)
while explorer.More():
    edge = explorer.Current()
    curve_adaptor = BRepAdaptor_Curve(edge)
    curve_edge = Edge(edge)
    curvatures = []
    _lower_bound, _upper_bound = curve_adaptor.FirstParameter(), curve_adaptor.LastParameter()

    num_eval_points = 100
    npts = GCPnts_UniformAbscissa(curve_adaptor, num_eval_points, _lower_bound, _upper_bound)
    if npts.IsDone():
        for i in range(1, npts.NbPoints() + 1):
            param = npts.Parameter(i)
            curvature = curve_edge.DiffGeom.curvature(param)
            curvatures.append(curvature)
            # Print or store the curvature value at each evaluation point
            print("Parameter:", param, "Curvature:", curvature)

    # Print all curvature values calculated for the current edge
    print("Curvatures for current edge:", curvatures)

    explorer.Next()

Geometry File:

Changed the file ending to .txt as Github doesn't allow uploads of .step files. Attached TXT file: sin_curve.txt

Any assistance from the community in diagnosing and resolving this issue would be greatly appreciated. Thank you in advance for your help!