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I've computed the intersection of a plane with some lines. It looks OK until I try to make a 3D graph from intersec_lines.

alpha = Pi/5;
r1 = 5;
r2 = 2;
h = 3;
n = 20;
plane = InfinitePlane[{{0, 0, 0}, {Cos[alpha], 0, Sin[alpha]}, {0, 1, 0}}];
lines = 
  Table[
    InfiniteLine[
      {r1*Cos[2*Pi*x/n], r1*Sin[2*Pi*x/n], 0}, 
      {r2*Cos[2*Pi*x/n], r2*Sin[2*Pi*x/n], h}], 
   {x, n}];
intersec_points = NSolve[{x, y, z} ∈ plane && {x, y, z} ∈ #]& /@ lines

Does anyone know how to do it? It seem it should be pretty basic, but I'm just starting to use Mathematica.

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  • 2
    $\begingroup$ Do not use _ in variable names, since _ has a special meaning in Mathematica. $\endgroup$
    – J. M.'s persistent exhaustion ♦
    Sep 29, 2018 at 14:06
  • $\begingroup$ To make it even clearer: Your code works except the variable named in not allowed because it has "_" in it. Then you have to write {x,y,z} /. Flatten[intersecPoints, 1] to get a list of points. $\endgroup$
    – C. E.
    Sep 29, 2018 at 16:17

1 Answer 1

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Using RegionIntersection[] is the most straightforward route for finding the intersection points:

With[{α = π/5, r1 = 5, r2 = 2, h = 3, n = 20},
     plane = InfinitePlane[{{0, 0, 0}, {Cos[α], 0, Sin[α]}, {0, 1, 0}}];
     lines = Table[InfiniteLine[{r1 Cos[2 π x/n], r1 Sin[2 π x/n], 0},
                                {r2 Cos[2 π x/n], r2 Sin[2 π x/n], h}], {x, n}];]

pts = RegionIntersection[plane, #] & /@ lines;

Graphics3D[{plane, lines, Sphere[#, 1/4] & @@@ pts}, Axes -> True, PlotRange -> 10]

intersection points of a cone and a plane

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