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module URDF | ||
using Multibody | ||
using LightXML | ||
using StaticArrays | ||
using Rotations | ||
using LinearAlgebra: ×, I, norm, normalize | ||
using Graphs | ||
using MetaGraphsNext | ||
using JuliaFormatter | ||
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function LightXML.find_element(x::XMLElement, n::AbstractString, ns::AbstractString...) | ||
inner = find_element(x, n) | ||
inner === nothing && return nothing | ||
find_element(inner, ns...) | ||
end | ||
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function parse_scalar(::Type{T}, e::XMLElement, name::String) where {T} | ||
parse(T, attribute(e, name)) | ||
end | ||
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function parse_scalar(::Type{T}, e, name::String, default::String) where {T} | ||
parse(T, e == nothing ? default : attribute(e, name)) | ||
end | ||
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function parse_vector(::Type{T}, e::Union{XMLElement, Nothing}, name::String, default::String) where {T} | ||
usedefault = e == nothing || attribute(e, name) == nothing | ||
[parse(T, str) for str in split(usedefault ? default : attribute(e, name))] | ||
end | ||
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function parse_color(xml_link, default) | ||
color_elem = find_element(xml_link, "visual", "material", "color") | ||
parse_vector(Float64, color_elem, "rgba", "1 0 0 1") | ||
end | ||
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function parse_inertia_mat(xml_inertia::XMLElement) | ||
ixx = parse_scalar(Float64, xml_inertia, "ixx", "0") | ||
ixy = parse_scalar(Float64, xml_inertia, "ixy", "0") | ||
ixz = parse_scalar(Float64, xml_inertia, "ixz", "0") | ||
iyy = parse_scalar(Float64, xml_inertia, "iyy", "0") | ||
iyz = parse_scalar(Float64, xml_inertia, "iyz", "0") | ||
izz = parse_scalar(Float64, xml_inertia, "izz", "0") | ||
[ixx ixy ixz; ixy iyy iyz; ixz iyz izz] | ||
end | ||
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function parse_pose(xml_pose::Nothing) | ||
rot = one(RotMatrix3{Float64}) | ||
trans = zeros(3) | ||
rot, trans | ||
end | ||
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function parse_pose(xml_pose::XMLElement) | ||
rpy = parse_vector(Float64, xml_pose, "rpy", "0 0 0") | ||
rot = RotMatrix(RotZYX(rpy[3], rpy[2], rpy[1])) | ||
trans = parse_vector(Float64, xml_pose, "xyz", "0 0 0") | ||
rot, trans | ||
end | ||
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function parse_joint(xml_joint::XMLElement) | ||
urdf_joint_type = attribute(xml_joint, "type") | ||
name = getname(xml_joint) | ||
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R, r = parse_pose(find_element(xml_joint, "origin")) | ||
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connections = "" | ||
if urdf_joint_type == "revolute" || urdf_joint_type == "continuous" | ||
axis = parse_vector(Float64, find_element(xml_joint, "axis"), "xyz", "1 0 0") | ||
damping = parse_scalar(Float64, find_element(xml_joint, "dynamics"), "damping", "0") | ||
if iszero(damping) | ||
components = "$name = URDFRevolute(; r=$r, R=$R, n=$axis)" | ||
else | ||
components = """ | ||
$name = URDFRevolute(; r=$r, R=$R, n=$axis, axisflange=true) | ||
$(name)_damper = Rotational.Damper(; d=$damping) | ||
""" | ||
connections = """ | ||
connect($name.support, $(name)_damper.flange_a) | ||
connect($(name)_damper.flange_b, $name.axis) | ||
""" | ||
end | ||
elseif urdf_joint_type == "prismatic" | ||
axis = parse_vector(T, find_element(xml_joint, "axis"), "xyz", "1 0 0") | ||
damping = parse_scalar(Float64, find_element(xml_joint, "dynamics"), "damping", "0") | ||
if iszero(damping) | ||
components = "$name = URDFPrismatic(; r=$r, R=$R, n=$axis)" | ||
else | ||
components = """ | ||
$name = URDFPrismatic(; r=$r, R=$R, n=$axis, axisflange=true) | ||
$(name)_damper = Translational.Damper(; d=$damping) | ||
""" | ||
connections = """ | ||
connect($name.support, $(name)_damper.flange_a) | ||
connect($(name)_damper.flange_b, $name.axis) | ||
""" | ||
end | ||
elseif urdf_joint_type == "floating" | ||
components = "$name = FreeMotion()" | ||
connections = "connect(world.frame_b, $name.frame_a)" | ||
elseif urdf_joint_type == "fixed" | ||
if norm(r) == 0 && R == I | ||
components = "$name = NullJoint()" # Null joint | ||
elseif R == I(3) | ||
components = "$name = FixedTranslation(; r=$r)" | ||
else | ||
components = "$name = FixedTranslation(; r=$r)" | ||
@warn "Ignoring rotation of joint $name" | ||
# R = RotMatrix3(R) | ||
# components = "$name = FixedRotation(; r=$r, n = $(rotation_axis(R)), angle = $(rotation_angle(R)))" | ||
end | ||
elseif urdf_joint_type == "planar" | ||
urdf_axis = parse_vector(Float64, find_element(xml_joint, "axis"), "xyz", "1 0 0") | ||
# The URDF spec says that a planar joint allows motion in a | ||
# plane perpendicular to the axis. | ||
R = Rotations.rotation_between([0, 0, 1], urdf_axis) | ||
x_axis = R * [1, 0, 0] | ||
components = "$name = $(joint_type)(; n_x=$x_axis, n=$urdf_axis)" | ||
else | ||
error("joint type $(urdf_joint_type) not recognized") | ||
end | ||
components, connections | ||
end | ||
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function parse_inertia(xml_inertial::XMLElement) | ||
moment = parse_inertia_mat(find_element(xml_inertial, "inertia")) | ||
mass = parse_scalar(Float64, find_element(xml_inertial, "mass"), "value", "0") | ||
r_cm = parse_vector(Float64, find_element(xml_inertial, "origin"), "xyz", "0 0 0") | ||
# TODO: handle transformation of inertia | ||
mass, moment, r_cm | ||
end | ||
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getname(xml_link::XMLElement) = attribute(xml_link, "name") | ||
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function parse_geometry(xml_link::XMLElement) | ||
xml_geometry = find_element(xml_link, "visual", "geometry") | ||
if xml_geometry === nothing | ||
return 0.1, 1, :sphere | ||
elseif (cylinder = find_element(xml_geometry, "cylinder")) !== nothing | ||
radius = parse_scalar(Float64, cylinder, "radius", "0.1") | ||
length = parse_scalar(Float64, cylinder, "length", "1") | ||
geometry = (; radius, length) | ||
type = :cylinder | ||
elseif (box = find_element(xml_geometry, "box")) !== nothing | ||
size = parse_vector(Float64, box, "size", "1 1 1") | ||
geometry = (; size) | ||
type = :box | ||
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elseif (sphere = find_element(xml_geometry, "sphere")) !== nothing | ||
radius = parse_scalar(Float64, sphere, "radius", "0.1") | ||
geometry = (; radius) | ||
type = :sphere | ||
elseif (mesh = find_element(xml_geometry, "mesh")) !== nothing | ||
@warn "Mesh geometry is not yet supported, using cylinder instead" | ||
# filename = attribute(mesh, "filename") | ||
# scale = parse_scalar(Float64, mesh, "scale", "1") | ||
radius = 0.1 | ||
length = 0.1 | ||
geometry = (; radius, length) | ||
type = :cylinder | ||
end | ||
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return geometry, type | ||
end | ||
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function parse_body(graph, xml_link::XMLElement) | ||
xml_inertial = find_element(xml_link, "inertial") | ||
mass,inertia,r_cm = xml_inertial == nothing ? (0,0*I(3),zeros(3)) : parse_inertia(xml_inertial) | ||
linkname = getname(xml_link) | ||
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R, r = parse_pose(find_element(xml_link, "visual", "origin")) | ||
color = parse_color(xml_link, "1 0 0 1") | ||
geometry, type = parse_geometry(xml_link) | ||
if R != I | ||
@warn "Ignoring rotation of link $linkname" | ||
end | ||
if norm(r) == 0 || type === :sphere | ||
radius = geometry.radius | ||
"$(Symbol(linkname)) = Body(; m=$(mass), r_cm=$(r_cm), I_11 = $(inertia[1,1]), I_22 = $(inertia[2,2]), I_33 = $(inertia[3,3]), I_21 = $(inertia[2,1]), I_31 = $(inertia[3,1]), I_32 = $(inertia[3,2]), color=$(color), radius=$(radius), sparse_I=true)" | ||
elseif type === :cylinder | ||
(; radius, length) = geometry | ||
r = normalize(r)*length | ||
"$(Symbol(linkname)) = BodyShape(; r=$(r), m=$(mass), r_cm=$(r_cm), I_11 = $(inertia[1,1]), I_22 = $(inertia[2,2]), I_33 = $(inertia[3,3]), I_21 = $(inertia[2,1]), I_31 = $(inertia[3,1]), I_32 = $(inertia[3,2]), color=$(color), radius=$(radius), sparse_I=true)" | ||
elseif type === :box | ||
(; size) = geometry | ||
length = size[1] | ||
width = size[2] | ||
height = size[3] | ||
"$(Symbol(linkname)) = BodyBox(; r=$(r), m=$(mass), r_cm=$(r_cm), body.I_11 = $(inertia[1,1]), body.I_22 = $(inertia[2,2]), body.I_33 = $(inertia[3,3]), body.I_21 = $(inertia[2,1]), body.I_31 = $(inertia[3,1]), body.I_32 = $(inertia[3,2]), color=$(color), length=$(length), width=$(width), height=$(height), sparse_I=true)" | ||
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end | ||
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end | ||
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default_modelname(filename) = uppercasefirst(splitext(basename(filename))[1]) | ||
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""" | ||
urdf2multibody(filename::AbstractString; extras=false, out=nothing, worldconnection = :rigid) | ||
Example usage: | ||
``` | ||
urdf2multibody(joinpath(dirname(pathof(Multibody)), "..", "test", "urdf", "doublependulum.urdf"), extras=true, out="/tmp/urdf_import.jl") | ||
``` | ||
## Keyword arguments | ||
- `extras=false`: If `true`, the generated code will include package imports, a simulation of the model and a rendering of the model. | ||
- `out=nothing`: If provided, the generated code will be written to this file, otherwise the string will only be returned. | ||
- `worldconnection=:rigid`: If `:rigid`, the world frame will be connected to the root link with a rigid connection. If a joint constructor is provided, this component will be instantiated and the root link is connected to the world through this, e.g., `worldconnection = FreeMotion`, `()->Prismatic(n=[0, 1, 0])` etc. | ||
- `modelname`: The name of the model, default is the name of the URDF file with the extension removed and the first letter upper case. | ||
""" | ||
function Multibody.urdf2multibody(filename::AbstractString; extras=false, out=nothing, worldconnection = :rigid, modelname = default_modelname(filename)) | ||
gravity = 9.81 | ||
floating::Bool = false | ||
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xdoc = parse_file(filename) | ||
xroot = LightXML.root(xdoc) | ||
@assert LightXML.name(xroot) == "robot" | ||
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xml_links = get_elements_by_tagname(xroot, "link") | ||
xml_joints = get_elements_by_tagname(xroot, "joint") | ||
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# create graph structure of XML elements | ||
graph = MetaGraph(DiGraph(), label_type=String, vertex_data_type=eltype(xml_links), edge_data_type=eltype(xml_joints)) | ||
for (i,vertex) in enumerate(xml_links) | ||
# add_vertex!(graph) | ||
graph[attribute(vertex, "name")] = vertex | ||
end | ||
name_to_vertex = Dict(attribute(v, "name") => i for (i,v) in enumerate(xml_links)) | ||
for xml_joint in xml_joints | ||
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parent = attribute(find_element(xml_joint, "parent"), "link") | ||
child = attribute(find_element(xml_joint, "child"), "link") | ||
graph[parent, child] = xml_joint | ||
end | ||
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cycles = simplecycles(graph) | ||
if !isempty(cycles) | ||
@info("The mechanism has kinematic loops. Kinematic loops must be broken manually, see https://juliacomputing.github.io/Multibody.jl/dev/examples/kinematic_loops/ for more info. The following loops were found", cycles) | ||
end | ||
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# Parse all joints and possible extra connections due to axisflanges | ||
joints_extraconnections = map(xml_joints) do l | ||
parse_joint(l) | ||
end | ||
joints = first.(joints_extraconnections) | ||
extra_connections = filter(!isempty, last.(joints_extraconnections)) | ||
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# Parse all bodies | ||
bodies = map(xml_links) do l | ||
parse_body(graph, l) | ||
end | ||
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roots = [v for v in vertices(graph) if indegree(graph, v) == 0] | ||
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connections = map(edges(graph)) do e | ||
src_link = label_for(graph, e.src) | ||
dst_link = label_for(graph, e.dst) | ||
joint = attribute(graph[src_link, dst_link], "name") | ||
"""connect($(src_link).frame_a, $(joint).frame_a) | ||
connect($(joint).frame_b, $(dst_link).frame_a)""" | ||
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end | ||
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for root in roots | ||
if worldconnection == :rigid | ||
pushfirst!(connections, "connect(world.frame_b, $(getname(xml_links[root])).frame_a)") | ||
elseif worldconnection isa Function | ||
push!(joints, "world_connection = $(nameof(worldconnection))()") | ||
push!(connections, "connect(world.frame_b, world_connection.frame_a)") | ||
push!(connections, "connect(world_connection.frame_b, $(getname(xml_links[root])).frame_a)") | ||
end | ||
end | ||
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s = if extras | ||
""" | ||
using ModelingToolkit, Multibody, JuliaSimCompiler, OrdinaryDiffEq, Plots | ||
import ModelingToolkit: t_nounits as t, D_nounits as D | ||
W(args...; kwargs...) = Multibody.world | ||
""" | ||
else | ||
"" | ||
end | ||
s = s * """ | ||
@mtkmodel $(modelname) begin | ||
@components begin | ||
world = W() | ||
$(join(bodies, "\n")) | ||
$(join(joints, "\n")) | ||
end | ||
@equations begin | ||
$(join(connections, "\n")) | ||
$(join(extra_connections, "\n")) | ||
end | ||
end | ||
""" | ||
if extras | ||
s = s * """ | ||
@named model = $(modelname)() | ||
model = complete(model) | ||
ssys = structural_simplify(IRSystem(model)) | ||
prob = ODEProblem(ssys, [], (0.0, 10.0)) | ||
sol = solve(prob, FBDF()) | ||
plot(sol) |> display | ||
import GLMakie | ||
first(Multibody.render(model, sol, 0, show_axis=true)) | ||
""" | ||
end | ||
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s = JuliaFormatter.format_text(s, align_assignment=true, align_struct_field=true, align_conditional=true, align_pair_arrow=true) | ||
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out === nothing && return s | ||
write(out, s) | ||
s | ||
end | ||
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end |