# BRepExtrema_DistShapeShape

I have have a cylinder of diameter 80 with axis vector (200,-200,170) starting at origin and intersecting a plane offset by -200 from ZX(along y). Picture attached. Intersection is an ellipse and I was testing if I am getting correct distances to other two planes, one offset from YX by -70 (along z) and the other by 350 (along z). Creo2 (Pro/Engineer) gives distances to planes 127.50238101 and 187.50238101, but the code bellow gives

NofSol = 1
Ellipse center @: 200 -200 170
distance to front plane = 282.745 distance to back plane = 137.255

Ellipse center is correct, but the distances are not. Furthermore, for vector of the cylinder axis (0,-200,0) which is just a cylinder along y axis so the intersection is a circle. One point is correct only giving distance 30, the other distance should be 310.

NofSol = 1
Circle center @: 0 -200 0
distance to front plane = 30 distance to back plane = 390

This is all using 6.7.1. I want to think that I am doing something wrong, but I don't see what that might be. Would anybody be willing to run the function bellow and investigate? Thank you in advance.

getStngPts(200,70,350,200,-200,170,80);
getStngPts(200,70,350,0,-200,0,80);

to the function

void getStngPts(double top,double front,double back,double stZbdyAx1, double stZbdyAx2,double stZbdyAx3, double stDia){
gp_Vec xUnit(1,0,0);
gp_Vec yUnit(0,1,0);
gp_Vec zUnit(0,0,1);

gp_Pnt top_pt(0,-top,0);
gp_Pnt front_pt(0,0,-front);
gp_Pnt back_pt(0,0,back);

gp_Pln top_pln(top_pt,gp_Dir(yUnit));
gp_Pln front_pln(front_pt,gp_Dir(zUnit));
gp_Pln back_pln(back_pt,gp_Dir(zUnit));

gp_Pnt orig(0,0,0);
gp_Dir stAxDir(gp_XYZ(stZbdyAx1,stZbdyAx2,stZbdyAx3));
gp_Ax3 stAxis(orig,stAxDir);

gp_Cylinder stCyl(stAxis,stDia/2.0);
std::cout IntAna_ResultType tp=Intrc.TypeInter();

gp_Circ elC;
gp_Elips elE;
TopoDS_Edge elEdge;

if(IntAna_Circle == tp){
elC=Intrc.Circle(1);
std::cout elEdge=BRepBuilderAPI_MakeEdge(elC);
}else{
elE=Intrc.Ellipse(1);
std::cout elEdge=BRepBuilderAPI_MakeEdge(elE);
}

TopoDS_Face frontFace=BRepBuilderAPI_MakeFace(front_pln);
TopoDS_Face backFace=BRepBuilderAPI_MakeFace(back_pln);

BRepExtrema_DistShapeShape dist2front(elEdge, frontFace);
BRepExtrema_DistShapeShape dist2back(elEdge, backFace);

double dist2f,dist2b;

if (dist2front.IsDone()) {
dist2f = dist2front.Value();
}
if (dist2back.IsDone()){
dist2b = dist2back.Value();
}

std::cout }

Attachments:

And it appears that some calculation in BRepExtrema_DistShapeShape is wrong in this case. Distance is to (I guess) a starting and ending point of the ellipse curve (different than what C++ code gave above). Here is the input to drawexe and the front view attached.

Draw[2]> cylinder c 0 0 0 200 -200 170 40
Draw[3]> plane p 0 -200 0 0 1 0
Draw[4]> intersect e c p
e
Draw[5]> plane pf 0 0 -70 0 0 1
Draw[6]> plane pb 0 0 350 0 0 1
Draw[8]> mkedge ed e
Draw[9]> mkface pfa pf
Draw[10]> distmini d1 ed pfa
d1_val d1
Draw[11]> mkface pba pb
Draw[13]> distmini d2 ed pba
d2_val d2
Draw[19]> dval d1_val
215.95836943965736
Draw[20]> dval d2_val
204.04163056034264

Attachments: