simple linux cam

gp_Pnt Util3D::calcLine(Handle(Geom_Line) l, double param) const {
  const gp_Ax1& axis  = l->Position();
  gp_Pnt        start(axis.Location().X(), axis.Location().Y(), axis.Location().Z());
  gp_Dir        dir(axis.Direction().X(), axis.Direction().Y(), axis.Direction().Z());
  gp_Pnt        ap = l->Value(param);
  gp_Pnt        rv = start;

  rv.SetX(start.X() + param * dir.X());
  rv.SetY(start.Y() + param * dir.Y());
  rv.SetZ(start.Z() + param * dir.Z());

  l->D0(param, ap);

  return rv;
  }

gp_Pnt Util3D::calcCircle(Handle(Geom_Circle) c, double param) const {
  const gp_Ax2& axis  = c->Position();
  gp_Pnt        center(axis.Location().X(), axis.Location().Y(), axis.Location().Z());
  gp_Dir        dir(axis.Direction());
  gp_Dir        xDir(axis.XDirection());
  gp_Dir        yDir(axis.YDirection());
  double        r  = c->Radius();
  double        cp = cos(param);
  double        sp = sin(param);
  gp_Pnt        ap = c->Value(param);
  gp_Pnt        rv;

  rv.SetX(center.X() + r * cp * xDir.X() + r * sp * yDir.X());
  rv.SetY(center.Y() + r * cp * xDir.Y() + r * sp * yDir.Y());
  rv.SetZ(center.Z() + r * cp * xDir.Z() + r * sp * yDir.Z());

  c->D0(param, ap);

  return rv;
  }

ElClib
//! Provides functions for basic geometric computations on
//! elementary curves such as conics and lines in 2D and 3D space.
//! This includes:
//! -   calculation of a point or derived vector on a 2D or
//! 3D curve where:
//! -   the curve is provided by the gp package, or
//! defined in reference form (as in the gp package),
//! and
//! -   the point is defined by a parameter,
//! -   evaluation of the parameter corresponding to a point
//! on a 2D or 3D curve from gp,
//! -   various elementary computations which allow you to
//! position parameterized values within the period of a curve.
//! Notes:
//! -   ElCLib stands for Elementary Curves Library.
//! -   If the curves provided by the gp package are not
//! explicitly parameterized, they still have an implicit
//! parameterization, analogous to that which they infer
//! for the equivalent Geom or Geom2d curves.

#include <Geom_Line.hxx>
#include <Geom_Circle.hxx>
#include <gp_Pnt.hxx>
#include <AIS_Shape.hxx>
#include <BRepBuilderAPI_MakeWire.hxx>
#include <BRepBuilderAPI_MakeEdge.hxx>
#include <ElCLib.hxx>

void OcctQtControl::on_pushButton_line_pressed()
{
    //! The line example :
    gp_Pnt a{0,0,0};
    gp_Pnt b{100,100,0};
    double linelenght=a.Distance(b);
    std::cout<<"linelenght:"<<linelenght<<std::endl;
    
    //! A non normalized line direction :
    gp_Dir dir(b.X()-a.X(), b.Y()-a.Y(), b.Z()-a.Z());

    //! Question is : how to calculate the "param" from given position.
    //!
    //! Input position : x50, y50, z50.
    //! Output

    gp_Pnt givenpos(50,50,0);
    const gp_Ax1 Axis(a,dir);
    double param=ElCLib::LineParameter(Axis,givenpos);

    std::cout<<"param:"<<param<<std::endl;
}

linelenght:141.421
param:70.7107

void function()
{
    //! The arc example :
    gp_Pnt start{0,0,0};
    gp_Pnt end{100,100,0};
    gp_Pnt center{50,0,0};

    gp_Ax2 PlaneTop=gp::XOY();
    PlaneTop.SetLocation(center);

    gp_Pnt givenleftpos(0,0,0);
    double param=ElCLib::CircleParameter(PlaneTop,givenleftpos);
    std::cout<<"leftpos param in radians:"<<param<<std::endl;

    gp_Pnt givenrightpos(100,0,0);
    param=ElCLib::CircleParameter(PlaneTop,givenrightpos);
    std::cout<<"rightpos param in radians:"<<param<<std::endl;
}

leftpos param in radians:3.14159
rightpos param in radians:0

OBJECT *lineA = new OBJECT();
lineA->setType(TYPE::line);
lineA->setPoints({{0,50,0},{100,50,0}});
occt_viewer->show_shape(lineA->getShape());

OBJECT *lineB = new OBJECT();
lineB->setType(TYPE::line);
lineB->setPoints({{50,0,0},{50,100,0}});
occt_viewer->show_shape(lineB->getShape());

gp_PntVec pvec;
lineA->getIntersections(*lineB,pvec);
pvec.push_back({100,1,1}); // To show the gp_Pnt vector usage.
pvec.print();

Output :
gp_PntVec at i:0 Value x: 50.000000 y: 50.000000 z: 0.000000
gp_PntVec at i:1 Value x: 100.000000 y: 1.000000 z: 1.000000

Handle(Geom_Line) line = Handle(Geom_Line)::DownCast(c);
     qDebug() << "cutCurve (line):" << first << " | " << last << " <> " << orientation;
     double dx  = p1.X() - p0.X();
     double dy  = p1.Y() - p0.Y();
     double gf  = dy / dx;
     double cf  = rMaster / sqrt(1 + gf * gf);
     double dr  = sqrt(dx * dx + dy * dy);
     double D   = p0.X() * p1.Y() - p1.X() * p0.Y();
     double res = rMaster * rMaster * dr * dr - D * D;
     double cx0 = cf * gf;
     double cy0 = -cf;
     double cx1 = -cx0;
     double cy1 = -cy0;

     if (res <= 0) qDebug() << "OUPS - fine calculations means no cutpoints?!?";
     qDebug() << "cutpoints: " << cx0 << " / " << cy0
              <<   "   and   " << cx1 << " / " << cy1;

     Core().view3D()->createAxisCross({cx0, cy0, 0}, 2, nullptr, Quantity_NOC_BLACK);
     Core().view3D()->createAxisCross({cx1, cy1, 0}, 2, nullptr, Quantity_NOC_WHITE);

     double param0 = ElCLib::Parameter(line->Lin(), {cx0, cy0, p0.Z()});
     double param1 = ElCLib::Parameter(line->Lin(), {cx1, cy1, p0.Z()});

     if (param0 >= first && param0 <= last) {
        qDebug() << "first cutpoint is part of line segment ==> "
                 << first << " <> "  << param0 << " <> " << last;
//        edge = BRepBuilderAPI_MakeEdge(c, {cx0, cy0, p0.Z()}, p1);
        }
     else if (param1 >= first && param1 <= last) {
        qDebug() << "second cutpoint is part of line segment ==> "
                 << first << " <> "  << param1 << " <> " << last;
//        edge = BRepBuilderAPI_MakeEdge(c, p0, {cx1, cy1, p0.Z()});
        }
     else {
        qDebug() << "?!?!? - none of the calculated cutpoints is inside of line parameters?!?"
                 << first << " <> " << param0 << "|" << param1 << last;
        edge = BRepBuilderAPI_MakeEdge(c, first, last);
        }