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frame_system.go
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frame_system.go
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package referenceframe
import (
"encoding/json"
"fmt"
"sort"
"github.com/golang/geo/r3"
"github.com/pkg/errors"
"go.uber.org/multierr"
pb "go.viam.com/api/robot/v1"
"go.viam.com/utils/protoutils"
"go.viam.com/rdk/logging"
spatial "go.viam.com/rdk/spatialmath"
)
// World is the string "world", but made into an exported constant.
const World = "world"
// defaultPointDensity ensures we use the default value specified within the spatialmath package.
const defaultPointDensity = 0.
// FrameSystem represents a tree of frames connected to each other, allowing for transformations between any two frames.
type FrameSystem interface {
// Name returns the name of this FrameSystem
Name() string
// World returns the frame corresponding to the root of the FrameSystem, from which other frames are defined with respect to
World() Frame
// FrameNames returns the names of all of the frames that exist in the FrameSystem
FrameNames() []string
// Frame returns the Frame in the FrameSystem corresponding to
Frame(name string) Frame
// AddFrame inserts a given Frame into the FrameSystem as a child of the parent Frame
AddFrame(frame, parent Frame) error
// RemoveFrame removes the given Frame from the FrameSystem
RemoveFrame(frame Frame)
// TracebackFrame traces the parentage of the given frame up to the world, and returns the full list of frames in between.
// The list will include both the query frame and the world referenceframe
TracebackFrame(frame Frame) ([]Frame, error)
// Parent returns the parent Frame for the given Frame in the FrameSystem
Parent(frame Frame) (Frame, error)
// Transform takes in a Transformable object and destination frame, and returns the pose from the first to the second. Positions
// is a map of inputs for any frames with non-zero DOF, with slices of inputs keyed to the frame name.
Transform(positions map[string][]Input, object Transformable, dst string) (Transformable, error)
// FrameSystemSubset will take a frame system and a frame in that system, and return a new frame system rooted
// at the given frame and containing all descendents of it. The original frame system is unchanged.
FrameSystemSubset(newRoot Frame) (FrameSystem, error)
// DivideFrameSystem will take a frame system and a frame in that system, and return a new frame system rooted
// at the given frame and containing all descendents of it, while the original has the frame and its
// descendents removed.
DivideFrameSystem(newRoot Frame) (FrameSystem, error)
// MergeFrameSystem combines two frame systems together, placing the world of systemToMerge at the attachTo frame in the frame system
MergeFrameSystem(systemToMerge FrameSystem, attachTo Frame) error
// ReplaceFrame finds the original frame which shares its name with replacementFrame. We then transfer the original
// frame's children and parentage to replacementFrame. The original frame is removed entirely from the frame system.
// replacementFrame is not allowed to exist within the frame system at the time of the call.
ReplaceFrame(replacementFrame Frame) error
}
// FrameSystemPart is used to collect all the info need from a named robot part to build the frame node in a frame system.
// FrameConfig gives the frame's location relative to parent,
// and ModelFrame is an optional ModelJSON that describes the internal kinematics of the robot part.
type FrameSystemPart struct {
FrameConfig *LinkInFrame
ModelFrame Model
}
// simpleFrameSystem implements FrameSystem. It is a simple tree graph.
type simpleFrameSystem struct {
name string
world Frame // separate from the map of frames so it can be detached easily
frames map[string]Frame
parents map[Frame]Frame
}
// NewEmptyFrameSystem creates a graph of Frames that have.
func NewEmptyFrameSystem(name string) FrameSystem {
worldFrame := NewZeroStaticFrame(World)
return &simpleFrameSystem{name, worldFrame, map[string]Frame{}, map[Frame]Frame{}}
}
// NewFrameSystem assembles a frame system from a set of parts and additional transforms.
func NewFrameSystem(name string, parts []*FrameSystemPart, additionalTransforms []*LinkInFrame) (FrameSystem, error) {
allParts := make([]*FrameSystemPart, 0, len(parts)+len(additionalTransforms))
allParts = append(allParts, parts...)
for _, tf := range additionalTransforms {
transformPart, err := LinkInFrameToFrameSystemPart(tf)
if err != nil {
return nil, err
}
allParts = append(allParts, transformPart)
}
// ensure that at least one frame connects to world if the frame system is not empty
if len(allParts) != 0 {
hasWorld := false
for _, part := range allParts {
if part.FrameConfig.Parent() == World {
hasWorld = true
break
}
}
if !hasWorld {
return nil, ErrNoWorldConnection
}
}
// Topologically sort parts
sortedParts, err := TopologicallySortParts(allParts)
if err != nil {
return nil, err
}
if len(sortedParts) != len(allParts) {
return nil, errors.Errorf(
"frame system has disconnected frames. connected frames: %v, all frames: %v",
getPartNames(sortedParts),
getPartNames(allParts),
)
}
fs := NewEmptyFrameSystem(name)
for _, part := range sortedParts {
// make the frames from the configs
modelFrame, staticOffsetFrame, err := createFramesFromPart(part)
if err != nil {
return nil, err
}
// attach static offset frame to parent, attach model frame to static offset frame
if err = fs.AddFrame(staticOffsetFrame, fs.Frame(part.FrameConfig.Parent())); err != nil {
return nil, err
}
if err = fs.AddFrame(modelFrame, staticOffsetFrame); err != nil {
return nil, err
}
}
return fs, nil
}
// World returns the base world referenceframe.
func (sfs *simpleFrameSystem) World() Frame {
return sfs.world
}
// Parent returns the parent frame of the input referenceframe. nil if input is World.
func (sfs *simpleFrameSystem) Parent(frame Frame) (Frame, error) {
if !sfs.frameExists(frame.Name()) {
return nil, NewFrameMissingError(frame.Name())
}
if parent := sfs.parents[frame]; parent != nil {
return parent, nil
}
return nil, NewParentFrameNilError(frame.Name())
}
// frameExists is a helper function to see if a frame with a given name already exists in the system.
func (sfs *simpleFrameSystem) frameExists(name string) bool {
if name == World {
return true
}
if _, ok := sfs.frames[name]; ok {
return true
}
return false
}
// RemoveFrame will delete the given frame and all descendents from the frame system if it exists.
func (sfs *simpleFrameSystem) RemoveFrame(frame Frame) {
delete(sfs.frames, frame.Name())
delete(sfs.parents, frame)
// Remove all descendents
for f, parent := range sfs.parents {
if parent == frame {
sfs.RemoveFrame(f)
}
}
}
// Frame returns the frame given the name of the referenceframe. Returns nil if the frame is not found.
func (sfs *simpleFrameSystem) Frame(name string) Frame {
if !sfs.frameExists(name) {
return nil
}
if name == World {
return sfs.world
}
return sfs.frames[name]
}
// TracebackFrame traces the parentage of the given frame up to the world, and returns the full list of frames in between.
// The list will include both the query frame and the world referenceframe, and is ordered from query to world.
func (sfs *simpleFrameSystem) TracebackFrame(query Frame) ([]Frame, error) {
if !sfs.frameExists(query.Name()) {
return nil, NewFrameMissingError(query.Name())
}
if query == sfs.world {
return []Frame{query}, nil
}
parents, err := sfs.TracebackFrame(sfs.parents[query])
if err != nil {
return nil, err
}
return append([]Frame{query}, parents...), nil
}
// FrameNames returns the list of frame names registered in the frame system.
func (sfs *simpleFrameSystem) FrameNames() []string {
var frameNames []string
for k := range sfs.frames {
frameNames = append(frameNames, k)
}
return frameNames
}
// AddFrame sets an already defined Frame into the system.
func (sfs *simpleFrameSystem) AddFrame(frame, parent Frame) error {
// check to see if parent is in system
if parent == nil {
return NewParentFrameNilError(frame.Name())
}
if !sfs.frameExists(parent.Name()) {
return NewFrameMissingError(parent.Name())
}
// check if frame with that name is already in system
if sfs.frameExists(frame.Name()) {
return NewFrameAlreadyExistsError(frame.Name())
}
// add to frame system
sfs.frames[frame.Name()] = frame
sfs.parents[frame] = parent
return nil
}
// Transform takes in a Transformable object and destination frame, and returns the pose from the first to the second. Positions
// is a map of inputs for any frames with non-zero DOF, with slices of inputs keyed to the frame name.
func (sfs *simpleFrameSystem) Transform(positions map[string][]Input, object Transformable, dst string) (Transformable, error) {
src := object.Parent()
if src == dst {
return object, nil
}
if !sfs.frameExists(src) {
return nil, NewFrameMissingError(src)
}
srcFrame := sfs.Frame(src)
if !sfs.frameExists(dst) {
return nil, NewFrameMissingError(dst)
}
var tfParent *PoseInFrame
var err error
if _, ok := object.(*GeometriesInFrame); ok && src != World {
// We don't want to apply the final transformation when that is taken care of by the geometries
// This has to do with the way we decided to tie geometries to frames for ease of defining them in the model_json file
// A frame is assigned a pose and a geometry and the two are not coupled together. This way you do can define everything relative
// to the parent frame. So geometries are tied to the frame they are assigned to but we do not want to actually transform them
// along the final transformation.
tfParent, err = sfs.transformFromParent(positions, sfs.parents[srcFrame], sfs.Frame(dst))
} else {
tfParent, err = sfs.transformFromParent(positions, srcFrame, sfs.Frame(dst))
}
if err != nil {
return nil, err
}
return object.Transform(tfParent), nil
}
// Name returns the name of the simpleFrameSystem.
func (sfs *simpleFrameSystem) Name() string {
return sfs.name
}
// MergeFrameSystem will combine two frame systems together, placing the world of systemToMerge at the "attachTo" frame in sfs.
// The frame where systemToMerge will be attached to must already exist within sfs, so should be added before Merge happens.
// Merging is necessary when including remote robots, dynamically building systems of robots, or mutating a robot after it
// has already been initialized. For example, two independent rovers, each with their own frame system, need to now know where
// they are in relation to each other and need to have their frame systems combined.
func (sfs *simpleFrameSystem) MergeFrameSystem(systemToMerge FrameSystem, attachTo Frame) error {
attachFrame := sfs.Frame(attachTo.Name())
if attachFrame == nil {
return NewFrameMissingError(attachTo.Name())
}
// make a map where the parent frame is the key and the slice of children frames is the value
childrenMap := map[Frame][]Frame{}
for _, name := range systemToMerge.FrameNames() {
child := systemToMerge.Frame(name)
parent, err := systemToMerge.Parent(child)
if err != nil {
if errors.Is(err, NewParentFrameNilError(child.Name())) {
continue
}
return err
}
childrenMap[parent] = append(childrenMap[parent], child)
}
// add every frame from systemToMerge to the base frame system.
queue := []Frame{systemToMerge.World()}
for len(queue) != 0 {
parent := queue[0]
queue = queue[1:]
children := childrenMap[parent]
for _, c := range children {
queue = append(queue, c)
if parent == systemToMerge.World() {
err := sfs.AddFrame(c, attachFrame) // attach c to the attachFrame
if err != nil {
return err
}
} else {
err := sfs.AddFrame(c, parent)
if err != nil {
return err
}
}
}
}
return nil
}
// FrameSystemSubset will take a frame system and a frame in that system, and return a new frame system rooted
// at the given frame and containing all descendents of it. The original frame system is unchanged.
func (sfs *simpleFrameSystem) FrameSystemSubset(newRoot Frame) (FrameSystem, error) {
newWorld := NewZeroStaticFrame(World)
newFS := &simpleFrameSystem{newRoot.Name() + "_FS", newWorld, map[string]Frame{}, map[Frame]Frame{}}
rootFrame := sfs.Frame(newRoot.Name())
if rootFrame == nil {
return nil, NewFrameMissingError(newRoot.Name())
}
newFS.frames[newRoot.Name()] = newRoot
newFS.parents[newRoot] = newWorld
var traceParent func(Frame) bool
traceParent = func(parent Frame) bool {
// Determine to which frame system this frame and its parent should be added
if parent == sfs.World() {
// keep in sfs
return false
} else if parent == newRoot || newFS.frameExists(parent.Name()) {
return true
}
return traceParent(sfs.parents[parent])
}
// Deleting from a map as we iterate through it is OK and safe to do in Go
for frame, parent := range sfs.parents {
var addNew bool
if parent == newRoot {
addNew = true
} else {
addNew = traceParent(parent)
}
if addNew {
newFS.frames[frame.Name()] = frame
newFS.parents[frame] = parent
}
}
return newFS, nil
}
// DivideFrameSystem will take a frame system and a frame in that system, and return a new frame system rooted
// at the given frame and containing all descendents of it, while the original has the frame and its
// descendents removed. For example, if there is a frame system with two independent rovers, and one rover goes offline,
// A user could divide the frame system to remove the offline rover and have the rest of the frame system unaffected.
func (sfs *simpleFrameSystem) DivideFrameSystem(newRoot Frame) (FrameSystem, error) {
newFS, err := sfs.FrameSystemSubset(newRoot)
if err != nil {
return nil, err
}
sfs.RemoveFrame(newRoot)
return newFS, nil
}
func (sfs *simpleFrameSystem) getFrameToWorldTransform(inputMap map[string][]Input, src Frame) (spatial.Pose, error) {
if !sfs.frameExists(src.Name()) {
return nil, NewFrameMissingError(src.Name())
}
// If src is nil it is interpreted as the world frame
var err error
srcToWorld := spatial.NewZeroPose()
if src != nil {
srcToWorld, err = sfs.composeTransforms(src, inputMap)
if err != nil && srcToWorld == nil {
return nil, err
}
}
return srcToWorld, err
}
// ReplaceFrame finds the original frame which shares its name with replacementFrame. We then transfer the original
// frame's children and parentage to replacementFrame. The original frame is removed entirely from the frame system.
// replacementFrame is not allowed to exist within the frame system at the time of the call.
func (sfs *simpleFrameSystem) ReplaceFrame(replacementFrame Frame) error {
var replaceMe Frame
if replaceMe = sfs.Frame(replacementFrame.Name()); replaceMe == nil {
return fmt.Errorf("%s not found in frame system", replacementFrame.Name())
}
if replaceMe == sfs.World() {
return errors.New("cannot replace the World frame of a frame system")
}
// get replaceMe's parent
replaceMeParent, err := sfs.Parent(replaceMe)
if err != nil {
return err
}
// remove replaceMe from the frame system
delete(sfs.frames, replaceMe.Name())
delete(sfs.parents, replaceMe)
for f, parent := range sfs.parents {
// replace frame with parent as replaceMe with replaceWith
if parent == replaceMe {
delete(sfs.parents, f)
sfs.parents[f] = replacementFrame
}
}
// add replacementFrame to frame system with parent of replaceMe
return sfs.AddFrame(replacementFrame, replaceMeParent)
}
// Returns the relative pose between the parent and the destination frame.
func (sfs *simpleFrameSystem) transformFromParent(inputMap map[string][]Input, src, dst Frame) (*PoseInFrame, error) {
// catch all errors together to allow for hypothetical calculations that result in errors
var errAll error
dstToWorld, err := sfs.getFrameToWorldTransform(inputMap, dst)
multierr.AppendInto(&errAll, err)
srcToWorld, err := sfs.getFrameToWorldTransform(inputMap, src)
multierr.AppendInto(&errAll, err)
if errAll != nil && (dstToWorld == nil || srcToWorld == nil) {
return nil, errAll
}
// transform from source to world, world to target parent
return NewPoseInFrame(dst.Name(), spatial.PoseBetween(dstToWorld, srcToWorld)), nil
}
// compose the quaternions from the input frame to the world referenceframe.
func (sfs *simpleFrameSystem) composeTransforms(frame Frame, inputMap map[string][]Input) (spatial.Pose, error) {
q := spatial.NewZeroPose() // empty initial dualquat
var errAll error
for sfs.parents[frame] != nil { // stop once you reach world node
// Transform() gives FROM q TO parent. Add new transforms to the left.
pose, err := poseFromPositions(frame, inputMap)
if err != nil && pose == nil {
return nil, err
}
multierr.AppendInto(&errAll, err)
q = spatial.Compose(pose, q)
frame = sfs.parents[frame]
}
return q, errAll
}
// StartPositions returns a zeroed input map ensuring all frames have inputs.
func StartPositions(fs FrameSystem) map[string][]Input {
positions := make(map[string][]Input)
for _, fn := range fs.FrameNames() {
frame := fs.Frame(fn)
if frame != nil {
positions[fn] = make([]Input, len(frame.DoF()))
}
}
return positions
}
// FrameSystemToPCD takes in a framesystem and returns a map where all elements are
// the point representation of their geometry type with respect to the world.
func FrameSystemToPCD(system FrameSystem, inputs map[string][]Input, logger logging.Logger) (map[string][]r3.Vector, error) {
vectorMap := make(map[string][]r3.Vector)
geometriesInWorldFrame, err := FrameSystemGeometries(system, inputs)
if err != nil {
logger.Debug(err)
}
for _, geometries := range geometriesInWorldFrame {
for _, geometry := range geometries.Geometries() {
vectorMap[geometry.Label()] = geometry.ToPoints(defaultPointDensity)
}
}
return vectorMap, nil
}
// FrameSystemGeometries takes in a framesystem and returns a map where all elements are GeometriesInFrames with a World reference frame.
func FrameSystemGeometries(fs FrameSystem, inputMap map[string][]Input) (map[string]*GeometriesInFrame, error) {
var errAll error
allGeometries := make(map[string]*GeometriesInFrame, 0)
for _, name := range fs.FrameNames() {
frame := fs.Frame(name)
inputs, err := GetFrameInputs(frame, inputMap)
if err != nil {
errAll = multierr.Append(errAll, err)
continue
}
geosInFrame, err := frame.Geometries(inputs)
if err != nil {
errAll = multierr.Append(errAll, err)
continue
}
if len(geosInFrame.Geometries()) > 0 {
transformed, err := fs.Transform(inputMap, geosInFrame, World)
if err != nil {
errAll = multierr.Append(errAll, err)
continue
}
allGeometries[name] = transformed.(*GeometriesInFrame)
}
}
return allGeometries, errAll
}
// ToProtobuf turns all the interfaces into serializable types.
func (part *FrameSystemPart) ToProtobuf() (*pb.FrameSystemConfig, error) {
if part.FrameConfig == nil {
return nil, ErrNoModelInformation
}
linkFrame, err := LinkInFrameToTransformProtobuf(part.FrameConfig)
if err != nil {
return nil, err
}
var modelJSON map[string]interface{}
if part.ModelFrame != nil {
bytes, err := part.ModelFrame.MarshalJSON()
if err != nil {
return nil, err
}
err = json.Unmarshal(bytes, &modelJSON)
if err != nil {
return nil, err
}
}
kinematics, err := protoutils.StructToStructPb(modelJSON)
if err != nil {
return nil, err
}
return &pb.FrameSystemConfig{
Frame: linkFrame,
Kinematics: kinematics,
}, nil
}
// ProtobufToFrameSystemPart takes a protobuf object and transforms it into a FrameSystemPart.
func ProtobufToFrameSystemPart(fsc *pb.FrameSystemConfig) (*FrameSystemPart, error) {
frameConfig, err := LinkInFrameFromTransformProtobuf(fsc.Frame)
if err != nil {
return nil, err
}
part := &FrameSystemPart{
FrameConfig: frameConfig,
}
if len(fsc.Kinematics.AsMap()) > 0 {
modelBytes, err := json.Marshal(fsc.Kinematics.AsMap())
if err != nil {
return nil, err
}
modelFrame, err := UnmarshalModelJSON(modelBytes, frameConfig.Name())
if err != nil {
if errors.Is(err, ErrNoModelInformation) {
return part, nil
}
return nil, err
}
part.ModelFrame = modelFrame
}
return part, nil
}
// LinkInFrameToFrameSystemPart creates a FrameSystem part out of a PoseInFrame.
func LinkInFrameToFrameSystemPart(transform *LinkInFrame) (*FrameSystemPart, error) {
if transform.Name() == "" || transform.Parent() == "" {
return nil, ErrEmptyStringFrameName
}
part := &FrameSystemPart{
FrameConfig: transform,
}
return part, nil
}
// createFramesFromPart will gather the frame information and build the frames from the given robot part.
func createFramesFromPart(part *FrameSystemPart) (Frame, Frame, error) {
if part == nil || part.FrameConfig == nil {
return nil, nil, errors.New("config for FrameSystemPart is nil")
}
var modelFrame Frame
var err error
// use identity frame if no model frame defined
if part.ModelFrame == nil {
modelFrame = NewZeroStaticFrame(part.FrameConfig.Name())
} else {
if part.ModelFrame.Name() != part.FrameConfig.Name() {
modelFrame = NewNamedFrame(part.ModelFrame, part.FrameConfig.Name())
} else {
modelFrame = part.ModelFrame
}
}
// staticOriginFrame defines a change in origin from the parent part.
// If it is empty, the new frame will have the same origin as the parent.
staticOriginName := part.FrameConfig.Name() + "_origin"
// By default, this
originFrame, err := part.FrameConfig.ToStaticFrame(staticOriginName)
if err != nil {
return nil, nil, err
}
staticOriginFrame, ok := originFrame.(*staticFrame)
if !ok {
return nil, nil, errors.New("failed to cast originFrame to a static frame")
}
// If the user has specified a geometry, and the model is a zero DOF frame (e.g. a gripper), we want to overwrite the geometry
// with the user-supplied one without changing the model transform
if len(modelFrame.DoF()) == 0 {
offsetGeom, err := staticOriginFrame.Geometries([]Input{})
if err != nil {
return nil, nil, err
}
pose, err := modelFrame.Transform([]Input{})
if err != nil {
return nil, nil, err
}
if len(offsetGeom.Geometries()) > 0 {
// If there are offset geometries, they should replace the static geometries, so the static frame is recreated with no geoms
noGeomFrame, err := NewStaticFrame(modelFrame.Name(), pose)
if err != nil {
return nil, nil, err
}
modelFrame = noGeomFrame
}
}
// Since the geometry of a frame system part is intended to be located at the origin of the model frame, we place it post-transform
// in the "_origin" static frame
return modelFrame, &tailGeometryStaticFrame{staticOriginFrame}, nil
}
// Names returns the names of input parts.
func getPartNames(parts []*FrameSystemPart) []string {
names := make([]string, len(parts))
for i, p := range parts {
names[i] = p.FrameConfig.Name()
}
return names
}
// TopologicallySortParts takes a potentially un-ordered slice of frame system parts and
// sorts them, beginning at the world node.
func TopologicallySortParts(parts []*FrameSystemPart) ([]*FrameSystemPart, error) {
// set up directory to check existence of parents
existingParts := make(map[string]bool, len(parts))
existingParts[World] = true
for _, part := range parts {
existingParts[part.FrameConfig.Name()] = true
}
// make map of children
children := make(map[string][]*FrameSystemPart)
for _, part := range parts {
parent := part.FrameConfig.Parent()
if !existingParts[parent] {
return nil, NewParentFrameMissingError(part.FrameConfig.Name(), parent)
}
children[part.FrameConfig.Parent()] = append(children[part.FrameConfig.Parent()], part)
}
topoSortedParts := []*FrameSystemPart{} // keep track of tree structure
// If there are no frames, return the empty list
if len(children) == 0 {
return topoSortedParts, nil
}
stack := make([]string, 0)
visited := make(map[string]bool)
if _, ok := children[World]; !ok {
return nil, ErrNoWorldConnection
}
stack = append(stack, World)
// begin adding frames to tree
for len(stack) != 0 {
parent := stack[0] // pop the top element from the stack
stack = stack[1:]
if _, ok := visited[parent]; ok {
return nil, errors.Errorf("the system contains a cycle, have already visited frame %s", parent)
}
visited[parent] = true
sort.Slice(children[parent], func(i, j int) bool {
return children[parent][i].FrameConfig.Name() < children[parent][j].FrameConfig.Name()
}) // sort alphabetically within the topological sort
for _, part := range children[parent] { // add all the children to the frame system, and to the stack as new parents
stack = append(stack, part.FrameConfig.Name())
topoSortedParts = append(topoSortedParts, part)
}
}
return topoSortedParts, nil
}
func poseFromPositions(frame Frame, positions map[string][]Input) (spatial.Pose, error) {
inputs, err := GetFrameInputs(frame, positions)
if err != nil {
return nil, err
}
return frame.Transform(inputs)
}