Added convenience constructors to convert Spherical etc

Author: Andy Ferris

README.md

@@ -63,9 +63,9 @@ differentiates with respect to components of `x`:
 ```
 
 Or perhaps we want to know how `y` will change with respect to changes of
-rotation angle:
+to the translation parameters:
 ```julia
-∂y_∂θ = transform_deriv_params(rot, x)
+∂y_∂θ = transform_deriv_params(trans, x)
 ```
 
 ### The interface
@@ -101,12 +101,9 @@ transformation chain.
 
 #### Coordinate types
 
-The package does not assume any specific coordinate types for Cartesian
-coordinates, and aims to accept any indexable container (such as `Vector`,
-`Tuple`, *FixedSizeArrays*' `FixedSizeVector{N}` or any other duck-typed vector).
-For speed, we recommend using a statically-sized container such as `Point{N}` or
-`Vec{N}` from *FixedSizeArrays*,  or even an `NTuple{N}`. However, it is
-attempted that the package will not change your data type.
+The package accepts any `AbstractVector` type for Cartesian coordinates (as
+well as *FixedSizeArrays* types in Julia v0.4 only). For speed, we recommend
+using a statically-sized container such as `SVector{N}` from *StaticArrays*.
 
 We do provide a few specialist coordinate types. The `Polar(r, θ)` type is a 2D
 polar representation of a point, and similarly in 3D we have defined
@@ -130,6 +127,9 @@ transformations:
 5. `CartesianFromCylindrical()`
 6. `CylindricalFromCartesian()`
 
+However, you may find it simpler to use the convenience constructors like
+`Polar(SVector(1.0, 2.0))`.
+
 #### Translations
 
 Translations can be be applied to Cartesian coordinates in arbitrary dimensions,

src/coordinatesystems.jl

@@ -55,6 +55,12 @@ Base.inv(::CartesianFromPolar) = PolarFromCartesian()
 compose(::PolarFromCartesian, ::CartesianFromPolar) = IdentityTransformation()
 compose(::CartesianFromPolar, ::PolarFromCartesian) = IdentityTransformation()
 
+# For convenience
+Base.convert(::Type{Polar}, v::AbstractVector) = PolarFromCartesian()(v)
+@inline Base.convert{V <: AbstractVector}(::Type{V}, p::Polar) = convert(V, CartesianFromPolar()(p))
+@inline Base.convert{V <: StaticVector}(::Type{V}, p::Polar) = convert(V, CartesianFromPolar()(p))
+
+
 #############################
 ### 3D Coordinate Systems ###
 #############################
@@ -216,3 +222,15 @@ compose(::CylindricalFromCartesian, ::CartesianFromSpherical)   = CylindricalFro
 compose(::CartesianFromCylindrical, ::CylindricalFromSpherical) = CartesianFromSpherical()
 compose(::CylindricalFromSpherical, ::SphericalFromCartesian)   = CylindricalFromCartesian()
 compose(::SphericalFromCylindrical, ::CylindricalFromCartesian) = SphericalFromCartesian()
+
+# For convenience
+Base.convert(::Type{Spherical}, v::AbstractVector) = SphericalFromCartesian()(v)
+Base.convert(::Type{Cylindrical}, v::AbstractVector) = CylindricalFromCartesian()(v)
+
+Base.convert{V <: AbstractVector}(::Type{V}, s::Spherical) = convert(V, CartesianFromSpherical()(s))
+Base.convert{V <: AbstractVector}(::Type{V}, c::Cylindrical) = convert(V, CartesianFromCylindrical()(c))
+Base.convert{V <: StaticVector}(::Type{V}, s::Spherical) = convert(V, CartesianFromSpherical()(s))
+Base.convert{V <: StaticVector}(::Type{V}, c::Cylindrical) = convert(V, CartesianFromCylindrical()(c))
+
+Base.convert(::Type{Spherical}, c::Cylindrical) = SphericalFromCylindrical()(c)
+Base.convert(::Type{Cylindrical}, s::Spherical) = CylindricalFromSpherical()(s)