View Issue Details

IDProjectCategoryView StatusDate SubmittedLast Update
0026378CommunityOCCT:Foundation Classespublic2015-06-29 14:192016-03-28 16:16
ReporterBenjaminBihler Assigned Tobugmaster  
PrioritylowSeveritymajor 
Status closedResolutionno change required 
PlatformLinuxOSDebian 6.0 
Product Version6.7.1 
Summary0026378: Curve tangent computed with D1 has wrong direction
DescriptionWhen computing the tangents of curves with D1, sometimes the direction is wrong.

In the example that I have attached, the direction at LastParameter() seemes flipped.
Steps To ReproducePlease check the attached STEP file. It contains one wire. I created tangents along this wire with the following code:

----------------------------------------------------------------------

Handle(BRepAdaptor_HCompCurve) wireAdaptor = new BRepAdaptor_HCompCurve(wire);

double parameter = wireAdaptor->FirstParameter();

while( parameter <= wireAdaptor->LastParameter())
{
gp_Pnt point;
gp_Vec tangent;

wireAdaptor->D1(parameter, point, tangent);
tangent.Normalize();

Business::Visualizer::getInstance()->visualizePoint(point);
Business::Visualizer::getInstance()->visualizeVector(point, tangent);

parameter +=0.01;
}

gp_Pnt point;
gp_Vec tangent;

wireAdaptor->D1(wireAdaptor->LastParameter(), point, tangent);
tangent.Normalize();

Business::Visualizer::getInstance()->visualizePoint(point);
Business::Visualizer::getInstance()->visualizeVector(point, tangent);

----------------------------------------------------------------------

Business::Visualizer::getInstance()->visualize... creates a vertex or an edge from the given objects and adds them to ther interactive context.

All tangents point into the same direction except the last one, which points towards the smaller interpolation parameters.
TagsNo tags attached.
Test case number

Attached Files

Activities

BenjaminBihler

2015-06-29 14:19

developer  

curve.stp (77,067 bytes)

BenjaminBihler

2016-02-03 11:45

developer   ~0050376

The issue is quite old, but the problem still exists. To ease debugging I have rewritten the test code. I hope that helps:

#include <TopoDS_Wire.hxx>
#include <TopoDS_Edge.hxx>
#include <TopoDS.hxx>
#include <STEPControl_Reader.hxx>
#include <Precision.hxx>
#include <TopExp_Explorer.hxx>
#include <BRepAdaptor_HCompCurve.hxx>
#include <BRepBuilderAPI_MakeWire.hxx>

#include <string>
#include <vector>
#include <iostream>

std::vector<TopoDS_Shape> importStep(const std::string file)
{
    std::vector<TopoDS_Shape> shapes;

    STEPControl_Reader reader;

    IFSelect_ReturnStatus status = reader.ReadFile(file.c_str());

    if (status == IFSelect_RetDone)
    {
        //Interface_TraceFile::SetDefault();
        bool failsonly = false;
        reader.PrintCheckLoad(failsonly, IFSelect_ItemsByEntity);

        int rootsNumber = reader.NbRootsForTransfer();
        reader.PrintCheckTransfer(failsonly, IFSelect_ItemsByEntity);
        for (Standard_Integer rootIndex = 1; rootIndex <= rootsNumber; rootIndex++)
        {
            //bool ok =
            reader.TransferRoot(rootIndex);
            int shapesNumber = reader.NbShapes();
            if (shapesNumber > 0)
            {
                for (int shapeIndex = 1; shapeIndex <= shapesNumber; shapeIndex++)
                {
                    TopoDS_Shape shape = reader.Shape(shapeIndex);

                    shapes.push_back(shape);
                }
            }
        }
    }
    else
    {
        throw "Could not read in file.";
    }

    return shapes;
}

int main(int, char**)
{
    std::vector<TopoDS_Shape> shapes = importStep("curve.stp");

    TopoDS_Edge edge;

    for (const auto& shape : shapes)
    {
        std::cout << "Searching edges." << std::endl;

        for (TopExp_Explorer edgeExplorer(shape, TopAbs_EDGE); edgeExplorer.More();
                edgeExplorer.Next())
        {
            edge = TopoDS::Edge(edgeExplorer.Current());
            std::cout << "Edge found." << std::endl;
            break;
        }
    }

    if (edge.IsNull())
    {
        std::cout << "Edge not found." << std::endl;
        return 1;
    }

    BRepBuilderAPI_MakeWire wireMaker;
    wireMaker.Add(edge);
    TopoDS_Wire wire = wireMaker.Wire();

    Handle(BRepAdaptor_HCompCurve) wireAdaptor = new BRepAdaptor_HCompCurve(wire);

    gp_Pnt dummyPoint;
    gp_Vec tangentAtStopPoint;
    gp_Vec tangentBeforeStopPoint;

    wireAdaptor->D1(wireAdaptor->LastParameter(), dummyPoint, tangentAtStopPoint);
    wireAdaptor->D1(wireAdaptor->LastParameter() - 0.01, dummyPoint,
            tangentBeforeStopPoint);

    const double angle = tangentAtStopPoint.Angle(tangentBeforeStopPoint);

    std::cout << "Angle: " << angle << std::endl;

    if (angle > M_PI / 2.0)
    {
        std::cerr << "ERROR: the tangent is flipped." << std::endl;

        std::cout << "Tangent at stop point: " << tangentAtStopPoint.X() << ", "
                << tangentAtStopPoint.Y() << ", " << tangentAtStopPoint.Z()
                << std::endl;

        std::cout << "Tangent before stop point: " << tangentBeforeStopPoint.X()
                << ", " << tangentBeforeStopPoint.Y() << ", "
                << tangentBeforeStopPoint.Z() << std::endl;
    }
    else
    {
        std::cout << "Everything is alright." << std::endl;
    }

    return 0;
}

BenjaminBihler

2016-03-22 17:25

developer   ~0051857

I have realized that erroneously I have entered "[OCCT] 6.7.1" as product version. Is this the reason why this issue is not considered? May I emphasize that this is still a problem? Since computing derivatives of curves is very central, this issue seems really important to me.

msv

2016-03-23 11:23

developer   ~0051868

This curve has a flipping at the end. You can see it in the snapshot made in Draw. I have zoomed in the view so that to see the very end of the curve. So, D1 is calculated right in this case.

msv

2016-03-23 11:23

developer  

curve.PNG (19,277 bytes)   

BenjaminBihler

2016-03-24 15:56

developer   ~0051965

Thank you very much for your answer. You are right, it seems as something went wrong during curve construction, but everything was fine with the tangent computation. I am sorry for the erroneous issue report.

msv

2016-03-24 18:35

developer   ~0051967

Dear bugmaster, please close this bug, no changes are required.

Issue History

Date Modified Username Field Change
2015-06-29 14:19 BenjaminBihler New Issue
2015-06-29 14:19 BenjaminBihler Assigned To => abv
2015-06-29 14:19 BenjaminBihler File Added: curve.stp
2016-02-03 11:45 BenjaminBihler Note Added: 0050376
2016-03-22 17:25 BenjaminBihler Note Added: 0051857
2016-03-23 07:11 aml Assigned To abv => msv
2016-03-23 11:23 msv Note Added: 0051868
2016-03-23 11:23 msv Status new => feedback
2016-03-23 11:23 msv File Added: curve.PNG
2016-03-24 15:56 BenjaminBihler Note Added: 0051965
2016-03-24 18:35 msv Note Added: 0051967
2016-03-24 18:35 msv Assigned To msv => bugmaster
2016-03-24 18:35 msv Priority normal => low
2016-03-24 18:35 msv Resolution open => no change required
2016-03-28 16:16 bugmaster Status feedback => closed