How do draw an angle that is not in the x-y plane?

[uzgit]

I need to draw an angle essentially from a->D->R in the figure, but I'm getting the issue that all the z-coordinates of the vertices defining the angle need to be the same. I have commented the angle at the end. Is there any way to draw this?

#import "@preview/cetz:0.3.4": *
#let matrice_landing_angles = canvas(length: 3cm, {
  import draw: *

  let radius_origin_negative = 0.5
  let radius_origin_positive = 1.5

  let origin = (0, 0, 0)
  let drone = (0, 0, 1.25)
  let ymax = (0, 2, 0)

  let landing_pad = (0.6, 0.75, 0)
  let landing_pad_y = (0, 0.75, 0)
  let landing_pad_angle = -19deg
  let landing_pad_radius = 0.75
  
  ortho(y: 0deg, x: -60deg, z: -55deg, {
    on-xy({
      grid((-radius_origin_negative, -radius_origin_negative), (radius_origin_positive, radius_origin_positive), step: 0.25, stroke: 0.125pt)
    })
    
    set-style(
      mark: (fill: black, scale: 2),
      stroke: (thickness: 0.4pt, cap: "round"),
      content: (padding: 1pt)
    )
    
    line((-0.75, 0, 0), (1.75, 0, 0), mark: (start: "stealth", end: "stealth"))
    content((1.75, 0, 0), anchor: "south-west", padding: 1mm, $x$)
  
    line((0, -0.75, 0), (0, 1.75, 0), mark: (start: "stealth", end: "stealth"))
    content((0, 1.75, 0), anchor: "west", padding: 1mm, $y$)
  
    line((0, 0, -0.75), (0, 0, 1.75), mark: (start: "stealth", end: "stealth"))
    content((0, 0, 1.75), anchor: "north", padding: 1mm, $z$)
  
    content(drone, $D$, anchor: "east", padding: 1mm)
    line(drone, landing_pad, stroke: (dash: "dashed"))
    line(origin, landing_pad, stroke: (dash: "dashed"))
  
    content((origin, 50%, drone), text(fill: red, $a$), anchor: "east", padding: 1mm)
  
    content((landing_pad, 60%, drone), text(fill: red, $R$), anchor: "north-west", padding: 2mm)
  
    angle.angle(origin, landing_pad, ymax, fill: aqua.lighten(50%), label-radius: 0.6, label: $phi$)
  
    angle.angle(landing_pad_y, landing_pad, ymax, fill: aqua.lighten(50%),
      label: $psi$, label-radius: 0.6, radius: 0.5)
  
    circle((0.6,0.75), radius: 1mm, fill: black)
    line(landing_pad, (landing_pad_radius * calc.cos(landing_pad_angle) + 0.75,  landing_pad_radius * calc.sin(landing_pad_angle) + 1, 0), mark: (fill: blue, end: "stealth"), stroke: blue)
    line(landing_pad_y, landing_pad, stroke: (dash: "dashed", paint: blue))

    content(landing_pad, anchor: "south-east", padding: 1mm, "LP")


    // how do I draw this angle
    // angle.angle(drone, landing_pad, origin, fill: aqua.lighten(50%),
    //   label: $theta$, label-radius: 0.6, radius: 0.5)

    // tried rotating things
    // ortho(x: 0deg, y: -0deg, z: 0deg, {
    //   angle.angle((0, 0, 1.25), (1, 0, 1.25), (0, 1, 1.25), fill: aqua.lighten(50%),
    //   label: $tau$, label-radius: 0.6, radius: 0.5)
    // })
  })
})

#figure(
  matrice_landing_angles,
  caption: [Relevant angles.]
)

[johannes-wolf]

Hack Alert! It is possible, but very ugly.
My solution:

• Create anchors for the points needed
• Outsides the ortho-view get the anchors coordinates
• Revert the current view transformation
• Remove the z-component

Allowing a z component in angle coordinats would be useful.
I should also add some function to get non-transformed anchor coordinates.
Ortho returning anchors with a z!=0 seems to be not correct.

#import "@preview/cetz:0.3.4": *
#let matrice_landing_angles = canvas(length: 3cm, {
  import draw: *

  let radius_origin_negative = 0.5
  let radius_origin_positive = 1.5

  let origin = (0, 0, 0)
  let drone = (0, 0, 1.25)
  let ymax = (0, 2, 0)

  let landing_pad = (0.6, 0.75, 0)
  let landing_pad_y = (0, 0.75, 0)
  let landing_pad_angle = -19deg
  let landing_pad_radius = 0.75
  
  ortho(y: 0deg, x: -60deg, z: -55deg, name: "v", {
    on-xy({
      grid((-radius_origin_negative, -radius_origin_negative), (radius_origin_positive, radius_origin_positive), step: 0.25, stroke: 0.125pt)
    })
    
    set-style(
      mark: (fill: black, scale: 2),
      stroke: (thickness: 0.4pt, cap: "round"),
      content: (padding: 1pt)
    )
    
    line((-0.75, 0, 0), (1.75, 0, 0), mark: (start: "stealth", end: "stealth"))
    content((1.75, 0, 0), anchor: "south-west", padding: 1mm, $x$)
  
    line((0, -0.75, 0), (0, 1.75, 0), mark: (start: "stealth", end: "stealth"))
    content((0, 1.75, 0), anchor: "west", padding: 1mm, $y$)
  
    line((0, 0, -0.75), (0, 0, 1.75), mark: (start: "stealth", end: "stealth"))
    content((0, 0, 1.75), anchor: "north", padding: 1mm, $z$)
  
    content(drone, $D$, anchor: "east", padding: 1mm)
    line(drone, landing_pad, stroke: (dash: "dashed"))
    line(origin, landing_pad, stroke: (dash: "dashed"))
  
    content((origin, 50%, drone), text(fill: red, $a$), anchor: "east", padding: 1mm)
  
    content((landing_pad, 60%, drone), text(fill: red, $R$), anchor: "north-west", padding: 2mm)
  
    angle.angle(origin, landing_pad, ymax, fill: aqua.lighten(50%), label-radius: 0.6, label: $phi$)
  
    angle.angle(landing_pad_y, landing_pad, ymax, fill: aqua.lighten(50%),
      label: $psi$, label-radius: 0.6, radius: 0.5)
  
    circle((0.6,0.75), radius: 1mm, fill: black)
    line(landing_pad, (landing_pad_radius * calc.cos(landing_pad_angle) + 0.75,  landing_pad_radius * calc.sin(landing_pad_angle) + 1, 0), mark: (fill: blue, end: "stealth"), stroke: blue)
    line(landing_pad_y, landing_pad, stroke: (dash: "dashed", paint: blue))

    content(landing_pad, anchor: "south-east", padding: 1mm, "LP")

    anchor("landing_pad", landing_pad)
    anchor("drone", drone)
    anchor("origin", origin)
  })

  scope(ctx => {
    let (drone, landing_pad, origin) = coordinate.resolve(
      ctx, "v.drone", "v.landing_pad", "v.origin")
      .slice(1)
      .map(v => {
        // We do not want transformed coordinates
        v = util.revert-transform(ctx.transform, v)
        // Remove the z component
        (v.at(0), v.at(1), 0)
      })
    angle.angle(drone, origin, landing_pad, fill: aqua.lighten(50%),
      label: $theta$, label-radius: 0.6, radius: 0.5, inner: true)
  })
})

#figure(
  matrice_landing_angles,
  caption: [Relevant angles.]
)

[uzgit]

Wow, thank you very much for your lightning fast response! This works great!

It is possible, but very ugly.

If it's ugly and it works, it's beautiful!