Plotting a disk with a z-value different to zero

Question

I'm plotting a disk with ParametricPlot3d, but I need it to be drawn at z = 0.4, in order to join it with another plot.

ParametricPlot3D[
  {r*Sin[Pi/2]*Cos[ϕ], r*Sin[Pi/2]*Sin[ϕ], r*Cos[Pi/2]},
  {r, 0, 1}, {ϕ, 0, 2*Pi},
  Mesh -> None]

This is the result joining it with the other graph:

I tried with PlotRange -> {{-1, 1}, {-1, 1}, {0.4, 1}} but that just set the way it is graphed, doesn´t solve the problem:

I just need the disk to be graphed at z = 0.4 instead of z = 0.

Please help.

Answer 1

If you specify the BoxRatios you can see a cone rather than a disk. The cone is essentially at 0. It looks like a cone due to machine precision in calculating r*Cos[Pi/2] which is exactly 0.

r*Cos[Pi/2]

(* 0 *)

ParametricPlot3D[{r*Sin[Pi/2]*Cos[ϕ], r*Sin[Pi/2]*Sin[ϕ], 
  r*Cos[Pi/2]}, {r, 0, 1}, {ϕ, 0, 2*Pi}, Mesh -> None, 
 BoxRatios -> {1, 1, 1}]

Your disc is exactly at 0 if you Evaluate the argument.

ParametricPlot3D[
 Evaluate@{r*Sin[Pi/2]*Cos[ϕ], r*Sin[Pi/2]*Sin[ϕ], 
   r*Cos[Pi/2]}, {r, 0, 1}, {ϕ, 0, 2*Pi}, Mesh -> None, 
 BoxRatios -> {1, 1, 1}]

To draw a disc at z == 0.4 specify the z function as a constant.

ParametricPlot3D[{r*Sin[Pi/2]*Cos[ϕ], r*Sin[Pi/2]*Sin[ϕ], 0.4}, {r, 
  0, 1}, {ϕ, 0, 2*Pi}, Mesh -> None]