Default 3D coordinate system is left-handed?

[KronosTheLate]

Relevant issue: #274

The following screenshot shows how a simple 3D coordinate system I made appears to be left-handed:

Code:

#import "@preview/cetz:0.2.0"  // Drawing diagrams directly in Document
#[
  #cetz.canvas(length: 2cm, {
  import cetz.draw: *
  rotate(y: 30deg)

  let grid_sidelength = 3
  grid(
    (-grid_sidelength/2, -grid_sidelength/2, -grid_sidelength/2), 
    (grid_sidelength/2, grid_sidelength/2, -grid_sidelength/2), 
    step: 0.5, stroke: gray + 0.2pt
  )

  line((-grid_sidelength/2, 0, 0), (grid_sidelength/2, 0, 0), name: "xaxis", mark: (end: "stealth"))
  content((name: "xaxis", anchor: 98%), [#v(1.5em)$ x $])
  line((0, -grid_sidelength/2, 0), (0, grid_sidelength/2, 0), name: "yaxis", mark: (end: "stealth"))
  content((name: "yaxis", anchor: 98%), [#h(-0.9em)$y$])
  line((0, 0, -grid_sidelength/2), (0, 0, grid_sidelength/2), name: "zaxis", mark: (end: "stealth"))
  content((name: "zaxis", anchor: 98%), [#h(-1em)$z$], anchor: "south-east")

  let ccol = red.darken(30%)
  line((0, 0, 0), (1, 0, 0), name: "ihat", mark:(end: "stealth", fill: ccol), stroke: ccol)
  content((name: "ihat", anchor: 65%, ), text(ccol)[#v(1.5em)$hat(i)$])

  let ccol = green.darken(30%)
  line((0, 0, 0), (0, 1, 0), name: "jhat", mark:(end: "stealth", fill: ccol), stroke: ccol)
  content((name: "jhat", anchor: 65%), text(ccol)[#h(-0.75em)$hat(j)$])

  let ccol = blue.darken(30%)
  line((0, 0, 0), (0, 0, 1), name: "khat", mark:(end: "stealth", fill: ccol), stroke: ccol)
  content((name: "khat", anchor: 65%), text(ccol)[#v(-1em)$hat(k)$])
})]

This seems like an odd choice to me. I tried changing `z-up` and `xy-up` in `set-style`, but I could not see any difference. Am I doing it wrong, or is the default coordinate system left-handed?

P.S: Awesome package. Easy to use, reaults look great.

[johannes-wolf]

3D support is very limited right now. To set up your coordinate system, call set-transform(<matrix>) to overwrite the transformation matrix. We should definitely add some functions to set up 3D coordinate systems more easily.

The system is left-handed because TikZ' also is, tbh.
A scale(z: -1) should flip the coordinates.

Some elements, like marks, have z-up and xy-up style-keys to set up their orientation, but this does not change the coordinate system.

[KronosTheLate]

Thanks, scale(z: -1) works as expected.

I am super impressed by the limited 3D support, awesome work ^_^

As this is a young package, it is not too late to improve upon it's ancestors. Would it not make a lot of sense to make the default coordinate system right-handed, and basically all coordinate systems anyone works with are? If not, the burden of inverting the z-axis will be inherited by every user wanting to visualize a normal coordinate system, forever. Unless there is a clear benefit (other than consistency with TikZ), I would vote hard in the direction of changing the default.

[johannes-wolf]

@KronosTheLate what do you think about #504

[KronosTheLate]

It looks good to me! There are some details I feel unable to evaluate (due to lack of knowledge and experience), but that PR certainly closes this issue. I will hop on over to continue the discussion there.

[KronosTheLate]

Thanks for fixing this <3