0030722: Modeling Algorithms - BRepExtrema_DistShapeShape computes wrong distances

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0030722

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[OCCT] OCCT:Modeling Algorithms

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2019-05-21 15:37

2019-05-21 16:37

Reporter

BenjaminBihler

Assigned To

ifv

Priority

normal

Severity

minor

Status

assigned

Resolution

open

Platform

OS Version

Product Version

[OCCT] 7.3.0

Target Version

[OCCT] 7.4.0*

Fixed in Version

Summary

0030722: Modeling Algorithms - BRepExtrema_DistShapeShape computes wrong distances

Description

When computing the intersections of a wire and an edge, the result is wrong. Checking the wire's edges against the given edge shows that there is a major computation error.

Steps To Reproduce

Draw script:

restore Wire.brep w
restore Edge.brep e
explode w
mkcurve c1 w_1
mkcurve c2 e
extrema c1 c2

Original steps:

Please check the following program with the two uploaded files:

#include <TopoDS_Edge.hxx>
#include <TopoDS_Wire.hxx>
#include <BRepExtrema_DistShapeShape.hxx>
#include <TopoDS.hxx>
#include <Precision.hxx>
#include <TopExp_Explorer.hxx>
#include <BRepTools.hxx>
#include <BRep_Builder.hxx>
#include <BRepAdaptor_Curve.hxx>
#include <BRepAdaptor_CompCurve.hxx>
#include <BRepCheck_Analyzer.hxx>
#include <BRepBuilderAPI_MakeVertex.hxx>

#include <iostream>

int main(int, char**)
{
    BRep_Builder builder;

    TopoDS_Shape shape1;
    BRepTools::Read(shape1, "Edge.brep", builder);

    TopoDS_Shape shape2;
    BRepTools::Read(shape2, "Wire.brep", builder);

    TopoDS_Edge edge;
    TopoDS_Wire wire;

    for (TopExp_Explorer edgeExplorer(shape1, TopAbs_EDGE); edgeExplorer.More();
            edgeExplorer.Next())
    {
        edge = TopoDS::Edge(edgeExplorer.Current());
        break;
    }

    for (TopExp_Explorer wireExplorer(shape2, TopAbs_WIRE); wireExplorer.More();
            wireExplorer.Next())
    {
        wire = TopoDS::Wire(wireExplorer.Current());
        break;
    }

    if (edge.IsNull())
    {
        std::cerr << "Edge is null." << std::endl;
        exit(1);
    }

    if (wire.IsNull())
    {
        std::cerr << "Wire is null." << std::endl;
        exit(1);
    }

    BRepCheck_Analyzer edgeAnalyzer(edge);

    if (!edgeAnalyzer.IsValid())
    {
        std::cerr << "Edge is invalid." << std::endl;
        exit(1);
    }

    BRepCheck_Analyzer wireAnalyzer(wire);

    if (!wireAnalyzer.IsValid())
    {
        std::cerr << "Wire is invalid." << std::endl;
        exit(1);
    }

    BRepExtrema_DistShapeShape distanceComputer;
    distanceComputer.SetFlag(Extrema_ExtFlag_MIN);
    distanceComputer.LoadS1(wire);
    distanceComputer.LoadS2(edge);
    distanceComputer.Perform();

    if (!distanceComputer.IsDone())
    {
        std::cerr << "Calculation failed." << std::endl;
        exit(1);
    }

    if (2 != distanceComputer.NbSolution())
    {
        std::cout << "Two solutions are expected, but there are "
                << distanceComputer.NbSolution() << " solutions." << std::endl;
    }

    for (TopExp_Explorer edgeExplorer(wire, TopAbs_EDGE); edgeExplorer.More();
            edgeExplorer.Next())
    {
        TopoDS_Edge wireEdge = TopoDS::Edge(edgeExplorer.Current());

        BRepExtrema_DistShapeShape wireEdgeDistanceComputer;
        wireEdgeDistanceComputer.SetFlag(Extrema_ExtFlag_MIN);
        wireEdgeDistanceComputer.LoadS1(wireEdge);
        wireEdgeDistanceComputer.LoadS2(edge);
        wireEdgeDistanceComputer.Perform();

        double smallestDistance = std::numeric_limits<double>::max();

        BRepAdaptor_Curve adaptor(wireEdge);

        for (double parameter = adaptor.FirstParameter();
                parameter <= adaptor.LastParameter(); parameter += 0.01)
        {
            BRepExtrema_DistShapeShape edgePointDistanceComputer;
            edgePointDistanceComputer.SetFlag(Extrema_ExtFlag_MIN);
            edgePointDistanceComputer.LoadS1(edge);

            TopoDS_Vertex vertex = BRepBuilderAPI_MakeVertex(
                    adaptor.Value(parameter));

            edgePointDistanceComputer.LoadS2(vertex);
            edgePointDistanceComputer.Perform();

            const double pointDistance = edgePointDistanceComputer.Value();

            if (pointDistance < smallestDistance)
            {
                smallestDistance = pointDistance;
            }
        }

        if (smallestDistance
                < wireEdgeDistanceComputer.Value() - Precision::Confusion())
        {
            std::cout << "Error in distance computation: "
                    << wireEdgeDistanceComputer.Value()
                    << " has been computed but the distance is " << smallestDistance
                    << " at most!" << std::endl;
        }
    }

    return 0;
}

Notes
(0084508) BenjaminBihler (developer) 2019-05-21 15:41	There are quite a lot of similar issues like 0030164, 0030367, 0027087. After having been using Open CASCADE for several years, I would claim that BRepExtrema_DistShapeShape errors are a major quality issue of Open CASCADE.

(0084515) msv (developer) 2019-05-21 16:33	There is a real issue in extrema computation between the trimmed ellipse (first edge of the wire) and the trimmed line. It finds no solution, but must find the single solution. I have provided the Draw script in steps to reproduce.

Issue History
Date Modified	Username	Field	Change
2019-05-21 15:37	BenjaminBihler	New Issue
2019-05-21 15:37	BenjaminBihler	Assigned To	=> msv
2019-05-21 15:37	BenjaminBihler	File Added: Edge.brep
2019-05-21 15:37	BenjaminBihler	File Added: Wire.brep
2019-05-21 15:41	BenjaminBihler	Note Added: 0084508
2019-05-21 16:33	msv	Note Added: 0084515
2019-05-21 16:34	msv	Steps to Reproduce Updated	View Revisions
2019-05-21 16:37	msv	Assigned To	msv => ifv
2019-05-21 16:37	msv	Status	new => assigned

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