# Dashed line in a one variable parametric_plot3d

Say you have a 3d line parametric plot (or `parametric_plot3d`

with one variable). How can you stile the resulting plotted line in a dashed style?

Checked out the documentation and I noticed `parametric_plot3d`

has an option for `border_style`

. However it looks like this has no affect when the area is zero.

There appears to be `linestyle`

available to 2d plots but this has no effect in 3d plots whether specified directly or in `border_style`

.

I also tried giving the colour a colourmap via `colormaps.autumn`

but I get an error:

TypeError: unable to simplify to float approximation

### Example

Below is the specific example I'm trying to dash. It is the second `parametric_plot3d`

with the comments:

```
var(['x', 'y', 'z', 'u', 'v', 'r', 'theta'])
angle = 30 * pi / 180
radius = tan(angle)*z
show(
parametric_plot3d(
(
r*cos(theta),
r*sin(theta),
r/tan(30 * pi / 180)
),
(r, 0, radius(z = 1)),
(theta, 0, 2*pi),
opacity = 0.5
)
+ point3d((radius(z = 0.5), 0, 0.5), color = 'red')
+ parametric_plot3d(
(
radius(z = 0.5)*cos(theta),
radius(z = 0.5)*sin(theta),
0.5
),
(theta, 0, 2*pi),
# color = 'red', # Produces a solid red line
# color = (theta, colormaps.autumn) # Throws an error
# linestyle = '--', # Does not work
# boundary_style = { # Does not work
# 'thickness': 5,
# 'linestyle': '--',
# 'color': 'red'
# }
)
)
```