How to find the distance between a point and a curve or between two curve using extrema in OCC

senthilsp
Wed, 11/15/2006 - 07:34

Forums:

I am having two interpolated Geom2d_BSplineCurve curves.Using extrema , how i can find the distance between the two curves.

for my work , I doesn't need of any visualization.Basically I need only the normal distance values between the curves.

It would be grateful if explained with any sample code.

Thanks in advance.

rgds
Senthil

Rob Bachrach
Wed, 11/15/2006 - 14:46

The most reliable way is to create edges from your curves and use BRepExtrema_DistShapeShape. For example (untested):

TopoDS_Edge edge1 = BRepBuilderAPI_MakeEdge2d(curve1);
TopoDS_Edge edge2 = BRepBuilderAPI_MakeEdge2d(curve2);
BRepExtrema_DistShapeShape extrema(edge1, edge2);
if (extrema.IsDone()) minDist = extrema.Value();

senthilsp
Wed, 11/15/2006 - 15:04

hi Rob ,

my code as follow

Handle(TColgp_HArray1OfPnt2d) harray =
new TColgp_HArray1OfPnt2d (1,5); // sizing harray
harray->SetValue(1,gp_Pnt2d (7+ 0,0));
harray->SetValue(2,gp_Pnt2d (7+ 1,2));
harray->SetValue(3,gp_Pnt2d (7+ 2,3));
harray->SetValue(4,gp_Pnt2d (7+ 4,3));
harray->SetValue(5,gp_Pnt2d (7+ 5,5));
Geom2dAPI_Interpolate anInterpolation(harray,Standard_False,0.01);
anInterpolation.Perform();
Handle(Geom2d_BSplineCurve) SPL1 = anInterpolation.Curve();

Handle(TColgp_HArray1OfPnt2d) harray2 =
new TColgp_HArray1OfPnt2d (1,5); // sizing harray
harray2->SetValue(1,gp_Pnt2d (11+ 0,0));
harray2->SetValue(2,gp_Pnt2d (11+ 1,2));
harray2->SetValue(3,gp_Pnt2d (11+ 2,3));
harray2->SetValue(4,gp_Pnt2d (11+ 4,3));
harray2->SetValue(5,gp_Pnt2d (11+ 5,5));
Geom2dAPI_Interpolate anInterpolation2(harray2,Standard_True,0.01);
anInterpolation2.Perform();
Handle(Geom2d_BSplineCurve) SPL2 = anInterpolation2.Curve();

TopoDS_Edge edge1 = BRepBuilderAPI_MakeEdge2d(SPL1);
TopoDS_Edge edge2 = BRepBuilderAPI_MakeEdge2d(SPL2);
BRepExtrema_DistShapeShape extrema(edge1, edge2);
if (extrema.IsDone())
int minDist = extrema.Value();

while executing the code , i am receiving Zero in the minDist .

I am new to OCC , correct me if the code is not addressing to my requirements

Thanks in advance for effective inputs to address my requirements

rgds
Senthil

senthilsp
Wed, 11/15/2006 - 15:08

hi Rob ,

my code as follow

while executing the code , i am receiving Zero in the minDist .

I am new to OCC , correct me if the code is not addressing to my requirements

Thanks in advance for effective inputs to address my requirements

rgds
Senthil

Rob Bachrach
Wed, 11/15/2006 - 15:14

The computed distance is about 0.997. You are placing this value in an "int", so it is getting truncated to 0. Try placing the value in a "Standard_Real" or "double".

senthilsp
Wed, 11/15/2006 - 15:43

Hi Rob,

Thanks for your inputs to show the correct way.

is it possible to find the particular points which makes the closest distance?

similiarly how I can find the distance between a point and a Geom2d_BSplineCurve curve.

Need your inputs regarding the same.

rgds
Senthil

Rob Bachrach
Wed, 11/15/2006 - 16:11

Look at the documentation on BRepExtrema_DistShapeShape.
NbSolution() gives the number of point pairs giving the minimum distance.
PointOnShape1 & PointOnShape2 allow you to access the point pairs.
ParOnEdgeS1 & ParOnEdgeS2 allow you to access the parametric locations on the curves.

To find the distance between a point and the curve, make an edge from the curve and make a TopoDS_Vertex from the point. Then use the extrema as before.