Undesirable grid appears when ParametricPlot is exported as PDF

Question

Writing:

plot = ParametricPlot[{x, Min[1, 2] t}, {x, 0, 2}, {t, 0, 1}, 
                       PlotRange -> {{0, 2}, {-1, 2}}]

I get:

but if I write:

Export["test.pdf", plot]

I get:

How can I get the same image in test.pdf?

Answer 1

UPDATE: See more general solution in this answer.

---

You can solve this problem by joining the polygons using undocumented function Graphics`PolygonUtils`PolygonCombine:

plot = Normal@
   ParametricPlot[{x, Min[1, 2] t}, {x, 0, 2}, {t, 0, 1}, 
    PlotRange -> {{0, 2}, {-1, 2}}] /. 
  p : {__Polygon} :> Graphics`PolygonUtils`PolygonCombine[p];

Export["test.pdf", plot] // SystemOpen

Here is how the file is rendered by Adobe Acrobat:

(checked with version 11.1.0).

Answer 2

Another workaround is to remove transparency from the polygons by specifying the PlotStyle explicitly:

plot = ParametricPlot[{x, Min[1, 2] t}, {x, 0, 2}, {t, 0, 1}, 
  PlotRange -> {{0, 2}, {-1, 2}}, Mesh -> None, 
  PlotStyle -> RGBColor[{0.812, 0.851, 0.914, 1}]]

Now the PDF

Export["test.pdf", %] // SystemOpen

is rendered as