Cannot create 2D Cartesian points with specified units

General Usage
,
1 
using CoordRefSystems, Unitful

rand(Cartesian2D{NoDatum, typeof(1.0u"m")})

does not work.

2

What is your ultimate goal? The rand api in CoordRefSystems.jl is pretty low-level and mostly internal at this point.

3

I want to create synthetic scenes to test geometric inference algorithms. For that, I need to generate random data. I canโ€™t generate random data without default units, which seems limiting.

The Unitful types are not easy to parse (or understand). Unfortunately, I could not add a rand function that will allow me to specify units.

4 
using Meshes
using CoordRefSystems
using Unitful

rand(Point, crs=Cartesian2D, 100) |> LengthUnit(u"ft")

100-element Vector{Point{๐”ผ{2}, Cartesian2D{NoDatum, Quantity{Float64, ๐‹, Unitful.FreeUnits{(ft,), ๐‹, nothing}}}}}:
 Point(x: 1.22995723127453 ft, y: 1.2578581984621078 ft)
 Point(x: 3.2635361225527983 ft, y: 0.971571140767104 ft)
 Point(x: 1.1144842750799535 ft, y: 0.2029331909786202 ft)
 Point(x: 2.6062199812344695 ft, y: 1.858510920611926 ft)
 Point(x: 2.0589584140282247 ft, y: 0.41389288343385094 ft)
 Point(x: 3.216505822297655 ft, y: 2.2673788472511975 ft)
 Point(x: 2.41786630208288 ft, y: 0.9093777827293031 ft)
 โ‹ฎ
 Point(x: 2.926702134428096 ft, y: 0.6350027654665833 ft)
 Point(x: 0.5839771521068765 ft, y: 2.6268370350416834 ft)
 Point(x: 0.9673777618597657 ft, y: 0.028165002572651938 ft)
 Point(x: 0.7529699261753467 ft, y: 0.7977590577763877 ft)
 Point(x: 2.4358324180744475 ft, y: 1.354883318069243 ft)
 Point(x: 2.4433776979835145 ft, y: 2.717828820597342 ft)
5

No I want random points with units that I specify, not default u"m"

6

I shared an example above where the LengthUnit transform is used to change the units after creation of the random Point from Meshes.jl

7

Okay, yes, that works, but youโ€™re changing the default units from u"m" to u"ft." It seems you should be able to specify units as a type parameter to Cartesian2D, so this can be passed around as one type. I would like to specify the Cartesian coordinate system (with units) and then have the synthetic scene generated according to type, instead of carrying around separate type info for the units.

8

This would apply to Meshes as well, where random geometries are constructed.

9

Cartesian2D is an alias to Cartesian:

const Cartesian2D{Datum} = Cartesian{Datum,2}

The full type is

Cartesian{Datum,N,L<:Len} <: Basic{Datum}

where Len is another alias:

const Len{T} = Quantity{T,u"๐‹"}

You can read the source code here:

10

I understand, but the original code doesnโ€™t work when I specify L <: Len. I donโ€™t know why when the type is fully defined.

11

e.g. this doesnt work either:

rand(Cartesian{NoDatum,2,Quantity{Float64,u"๐‹"}})

which I would expect should.

12

The type that is generated by default is:

Cartesian{NoDatum,2,CoordRefSystems.Met{Float64}}

where Met is also an alias:

const Met{T} = Quantity{T,u"๐‹",typeof(m)}

You can create an alias for the unit you have in mind, and define the type likewise:

const Ft{T} = Quantity{T,u"๐‹",typeof(ft)}

Cartesian{NoDatum,2,Ft{Float64}}

The rand methods are only defined for default units with default machine precision (Float64).

13

Thanks for the responses.