# Parametrized Helicoid plot becomes a cone + "Arrow=True" is not working for 3-D

**URL:** <https://discourse.julialang.org/t/parametrized-helicoid-plot-becomes-a-cone-arrow-true-is-not-working-for-3-d/100735>\
**Category:** General Usage\
**Tags:** plotting\
**Created:** [June 23, 2023, 10:32am UTC](https://discourse.julialang.org/t/parametrized-helicoid-plot-becomes-a-cone-arrow-true-is-not-working-for-3-d/100735 "2023-06-23T10:32:31Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Freya\_the\_Goddess](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/freya_the_goddess/32/36835_2.png) [@Freya\_the\_Goddess](https://discourse.julialang.org/u/Freya_the_Goddess)\
**Post date:** [June 23, 2023, 10:32am UTC](https://discourse.julialang.org/t/parametrized-helicoid-plot-becomes-a-cone-arrow-true-is-not-working-for-3-d/100735/1 "2023-06-23T10:32:31Z")

</div>

Hi all,

I might misunderstood the parametrized conversion to the code from this site:

> **[An introduction to parametrized surfaces - Math Insight](https://mathinsight.org/parametrized_surface_introduction)**
>
> An introduction to how a vector-valued function of two variables can be viewed as parametrizing a surface. Interactive graphics illustrate the way in which the function maps a planar region onto a surface.

I follow the parametrized helicoid and it becomes a cone:

![Capture d’écran_2023-06-23_17-30-02](https://global.discourse-cdn.com/julialang/original/3X/c/5/c562287271789e5fefdf1c19954d2de450817732.png)

```julia
using Plots;
gr() 

function helicoid(r)   
    n = 100
    θ = range(0, 2π; length = n)
    u = range(0, 1; length = n)
    x = r*u*cos.(θ)'
    y = r*u*sin.(θ)'
    z = θ*ones(size(u))'
    return x, y, z
end
my_cg = cgrad([:red,:blue])
surface(helicoid(3), c=my_cg, label="helicoid", arrow=true, arrowsize=5)

```

another one, the `arrow=true` does not showing any arrow. I try with helix that is working and the arrow is not there.

```julia
using Plots;
gr() 
#plotlyjs()

# a helix is a curve in 3-dimensional space. 
# The following parametrisation in Cartesian coordinates defines a particular helix;

function helix(r)   
    n = 100
    θ = range(-10, 10; length = n)
    x = r*cos.(θ)
    y = r*sin.(θ)
    z = θ
    return x, y, z
end
my_cg = cgrad([:red,:blue])
plot(helix(5), c=my_cg, label="helix", arrow=true, arrowsize=5)

```

---

<div class="post-metadata">

**Author:** ![JM\_Beckers](https://sea2.discourse-cdn.com/julialang/user_avatar/discourse.julialang.org/jm_beckers/32/22482_2.png) [@JM\_Beckers](https://discourse.julialang.org/u/JM_Beckers)\
**Post date:** [June 23, 2023, 12:36pm UTC](https://discourse.julialang.org/t/parametrized-helicoid-plot-becomes-a-cone-arrow-true-is-not-working-for-3-d/100735/2 "2023-06-23T12:36:35Z")

</div>

using Plots;  
gr()

```julia
function helicoid(r)   
    n = 100
    θ = range(-2pi, 2π; length = n)
    u = range(-10, 10; length = n)
    x = r*u*cos.(θ)'
    y = r*u*sin.(θ)'
    z = ones(size(u))*θ'
    return x, y, z
end
my_cg = cgrad([:red,:blue])
surface(helicoid(3), label="helicoid")

```