class CableController():
def __init__(self, points, maxSpeed, minSpeed, tanAccelLim, normAccelLim,
smoothStopP, maxAlt):
# Maximum tangential acceleration along the cable, m/s^2
self.tanAccelLim = tanAccelLim
# Maximum acceleration normal to the cable, m/s^2
self.normAccelLim = normAccelLim
# Smoothness of stops at the endpoints and at targets along the cable
self.smoothStopP = smoothStopP
# Maximum speed along the cable, m/s
self.maxSpeed = maxSpeed
# Minimum speed along the cable, m/s
self.minSpeed = minSpeed
# Minimum allowable position.z, meters (AKA max altitude), Convert Altitude (NEU) to NED
if maxAlt is not None:
self.posZLimit = -maxAlt
else:
self.posZLimit = None
# Input speed
self.desiredSpeed = 0.
# Current speed along the cable, m/s
self.speed = 0.
# Catmull-Rom spline with added virtual tangency control points at either end
self.spline = CatmullRom([points[0] * 2 - points[1]] + points +
[points[-1] * 2 - points[-2]])
# Number of spline segments (should really come from CatmullRom)
self.numSegments = len(points) - 1
# Current position in P domain, parameter normalized to cable total arc length
self.currentP = 1.0
# Target position in P domain
self.targetP = self.currentP
# Previously reached target, once set
self.prevReachedTarget = None
# Current segment, ranges from 0 to # of segments-1
self.currentSeg, self.currentU = self.spline.arclengthToNonDimensional(
self.currentP)
# Current position as a Vector3, meters
self.position = self.spline.position(self.currentSeg, self.currentU)
# Current velocity as a Vector3, m/s
self.velocity = Vector3()
# Flag to indicate that the maximum altitude has been exceeded
self.maxAltExceeded = False
# Number of segments in curvature map
self.curvatureMapNumSegments = int(
math.ceil(self.spline.totalArcLength / CURVATURE_MAP_RES))
# Number of joints in curvature map
self.curvatureMapNumJoints = self.curvatureMapNumSegments + 1
# Curvature map joint positions in p domain
self.curvatureMapJointsP, self.curvatureMapSegLengthP = linspace(
0., 1., self.curvatureMapNumJoints, retstep=True)
# Curvature map segment length in meters
self.curvatureMapSegLengthM = self.curvatureMapSegLengthP * self.spline.totalArcLength
# Non-dimensional curvature map joint position (cache)
self.curvatureMapJointsNonDimensional = [
None for _ in range(self.curvatureMapNumJoints)
]
# Speed limits for each curvature map segment (cache)
self.curvatureMapSpeedLimits = [
None for _ in range(self.curvatureMapNumSegments)
]
# Thread lock on curvature map segments
self.curvatureMapLocks = [
threading.Lock() for _ in range(self.curvatureMapNumSegments)
]
self.curvatureMapSegmentsComputedLock = threading.Lock()
# number of map segments that have been computed by the curvatureMapThread
self.curvatureMapSegmentsComputed = 0
# flag that indicates to the thread to die
self.poisonPill = False
# setup a worker thread to compute map segment maximum speeds
self.curvatureMapThread = threading.Thread(
target=self._computeCurvatureMap)
self.curvatureMapThread.setDaemon(True)
# start the worker thread
self.curvatureMapThread.start()
def __del__(self):
self.poisonPill = True
self.curvatureMapThread.join(timeout=2)
# Public interface:
def reachedTarget(self):
'''Return True if we've reached the target, else False'''
return abs(self.currentP - self.targetP
) * self.spline.totalArcLength < TARGET_EPSILON_M
def setTargetP(self, targetP):
'''Interface to set a target P'''
self.targetP = targetP
def trackSpeed(self, speed):
'''Updates controller desired speed'''
self.desiredSpeed = speed
def update(self, dt):
'''Advances controller along cable by dt'''
# Speed always in direction of target
self.desiredSpeed = math.copysign(self.desiredSpeed,
self.targetP - self.currentP)
self.speed = constrain(self._constrainSpeed(self.desiredSpeed),
self.speed - self.tanAccelLim * dt,
self.speed + self.tanAccelLim * dt)
self._traverse(dt)
def setCurrentP(self, p):
'''Sets the controller's current P position on the cable'''
self.currentP = p
self.currentSeg, self.currentU = self.spline.arclengthToNonDimensional(
self.currentP)
def killCurvatureMapThread(self):
'''Sets poisonPill to True so the curvatureMapThread knows to die'''
self.poisonPill = True
# Internal functions:
def _computeCurvatureMap(self):
'''Computes curvature map, prioritizes map construction based on vehicle position and direction of motion'''
while True:
searchStart = self._getCurvatureMapSegment(self.currentP)
if self.speed > 0:
# Search ahead, then behind
for i in range(searchStart,
self.curvatureMapNumSegments) + list(
reversed(range(0, searchStart))):
if self._computeCurvatureMapSpeedLimit(i):
break
elif self.speed < 0:
# Search behind, then ahead
for i in list(reversed(range(0, searchStart + 1))) + range(
searchStart + 1, self.curvatureMapNumSegments):
if self._computeCurvatureMapSpeedLimit(i):
break
else: # speed == 0
# Search alternately ahead and behind
searchList = [
x for t in list(
itertools.izip_longest(
range(searchStart, self.curvatureMapNumSegments),
reversed(range(0, searchStart)))) for x in t
if x is not None
]
for i in searchList:
if self._computeCurvatureMapSpeedLimit(i):
break
# if all map segments have been computed then quit the thread
with self.curvatureMapSegmentsComputedLock:
if self.curvatureMapSegmentsComputed == self.curvatureMapNumSegments:
self.poisonPill = True
if self.poisonPill:
break
def _computeCurvatureMapSpeedLimit(self, mapSeg):
'''Computes speed limit for the requested map segment'''
with self.curvatureMapLocks[mapSeg]:
# if the speed limit has already been computed for this map segment, then don't do any work
if self.curvatureMapSpeedLimits[mapSeg] is not None:
return False
# if non-dimensional parameter has not yet been created for the associated left joint, then create it
if self.curvatureMapJointsNonDimensional[mapSeg] is None:
self.curvatureMapJointsNonDimensional[
mapSeg] = self.spline.arclengthToNonDimensional(
self.curvatureMapJointsP[mapSeg])
# if non-dimensional parameter has not yet been created for the associated right joint, then create it
if self.curvatureMapJointsNonDimensional[mapSeg + 1] is None:
self.curvatureMapJointsNonDimensional[
mapSeg + 1] = self.spline.arclengthToNonDimensional(
self.curvatureMapJointsP[mapSeg + 1])
# split returned non-dimensional parameter tuple (seg,u) into separate values
seg1, u1 = self.curvatureMapJointsNonDimensional[mapSeg]
seg2, u2 = self.curvatureMapJointsNonDimensional[mapSeg + 1]
# returns arc length for current spline segment, or the larger of the two segments if our map segment spans across multiple spline segments
maxSegLen = max(self.spline.arcLengths[seg1:seg2 + 1]) # m
# run a golden section search to find the segment,u pair for the point of maximum curvature in the requested map segment
# (segment,u) are stored as segment+u, e.g. segment 1, u = 0.25 -> 1.25
maxCurvatureSegU = goldenSection(
lambda x: -self.spline.curvature(int(x), x - int(x)),
seg1 + u1,
seg2 + u2,
tol=1e-1 / maxSegLen)
# run a golden section search to find the segment,u pair for the point of minimum Z (aka max altitude)
minPosZSegU = goldenSection(
lambda x: self.spline.position(int(x), x - int(x)).z,
seg1 + u1,
seg2 + u2,
tol=1e-1 / maxSegLen)
# split segment+u into segment,u and evaluate curvature at this point
maxCurvature = self.spline.curvature(
int(maxCurvatureSegU),
maxCurvatureSegU - int(maxCurvatureSegU))
#split segment+u into segment,u and evalute position.z at this point
minPosZ = self.spline.position(int(minPosZSegU), minPosZSegU -
int(minPosZSegU)).z #m
# this prevents the copter from traversing segments of the cable
# that are above its altitude limit
if self.posZLimit is not None and minPosZ < self.posZLimit:
self.maxAltExceeded = True
#this cable will breach the altitude limit, make the speed limit for this segment 0 to stop the vehicle
self.curvatureMapSpeedLimits[mapSeg] = 0.
else:
if maxCurvature != 0.:
# limit maxspeed by the max allowable normal acceleration at that point, bounded on the lower end by minSpeed
self.curvatureMapSpeedLimits[mapSeg] = max(
math.sqrt(self.normAccelLim / maxCurvature),
self.minSpeed)
else:
# if curvature is zero, means a straight segment
self.curvatureMapSpeedLimits[mapSeg] = self.maxSpeed
with self.curvatureMapSegmentsComputedLock:
self.curvatureMapSegmentsComputed += 1
return True
def _getCurvatureMapSpeedLimit(self, mapSeg):
'''Look up the speed limit for the requested map segment'''
# sanitize mapSeg
if mapSeg < 0 or mapSeg >= self.curvatureMapNumSegments:
return 0.
self._computeCurvatureMapSpeedLimit(mapSeg)
return self.curvatureMapSpeedLimits[mapSeg]
def _traverse(self, dt):
''' Advances the controller along the spline '''
spline_vel_unit = self.spline.velocity(self.currentSeg, self.currentU)
spline_vel_norm = spline_vel_unit.normalize()
# advances u by the amount specified by our speed and dt
self.currentU += self.speed * dt / spline_vel_norm
# handle traversing spline segments
if self.currentU > 1.:
if self.currentSeg < self.numSegments - 1:
self.currentSeg += 1
self.currentU = 0. # NOTE: this truncates steps which cross spline joints
else:
self.currentU = 1.
elif self.currentU < 0.:
if self.currentSeg > 0:
self.currentSeg -= 1
self.currentU = 1. # NOTE: this truncates steps which cross spline joints
else:
self.currentU = 0.
# calculate our currentP
self.currentP = self.spline.nonDimensionalToArclength(
self.currentSeg, self.currentU)[0]
# calculate our position and velocity commands
self.position = self.spline.position(self.currentSeg, self.currentU)
self.velocity = spline_vel_unit * self.speed
def _constrainSpeed(self, speed):
'''Looks ahead and behind current controller position and constrains to a speed limit'''
if speed > 0:
return min(self.maxSpeed, speed,
self._getPosSpeedLimit(self.currentP))
elif speed < 0:
return max(-self.maxSpeed, speed,
self._getNegSpeedLimit(self.currentP))
return speed
def _speedCurve(self, dist, speed):
'''Returns speed based on the sqrt function or a linear ramp (depending on dist)'''
linear_velocity = self.tanAccelLim / self.smoothStopP
linear_dist = linear_velocity / self.smoothStopP
if speed > linear_velocity:
return math.sqrt(2. * self.tanAccelLim *
(speed**2 / (2. * self.tanAccelLim) + dist))
else:
p1 = speed / self.smoothStopP
p2 = p1 + dist
if p2 > linear_dist:
return math.sqrt(2. * self.tanAccelLim *
(p2 - 0.5 * linear_dist))
else:
return p2 * self.smoothStopP
def _maxLookAheadDist(self):
'''Calculate how far it would take to come to a complete stop '''
linear_velocity = self.tanAccelLim / self.smoothStopP
linear_dist = linear_velocity / self.smoothStopP
if abs(self.speed) > linear_velocity:
return 0.5 * abs(
self.speed)**2 / self.tanAccelLim + 0.5 * linear_dist
else:
return abs(self.speed) / self.smoothStopP
def _getCurvatureMapSegment(self, p):
'''Get the curvature map segment index at the location p'''
return int(
min(math.floor(p / self.curvatureMapSegLengthP),
self.curvatureMapNumSegments - 1))
def _getDistToCurvatureMapSegmentBegin(self, p1, idx):
'''Get distance from p1 to the beginning of the idx curvature map segment in meters'''
p2 = self.curvatureMapJointsP[idx]
return abs(p1 - p2) * self.spline.totalArcLength
def _getDistToCurvatureMapSegmentEnd(self, p1, idx):
'''Get distance from p1 to the end of the idx curvature map segment in meters'''
p2 = self.curvatureMapJointsP[idx + 1]
return abs(p1 - p2) * self.spline.totalArcLength
def _getPosSpeedLimit(self, p):
'''Returns speed limit for a requested arc length normalized parameter, p, moving in the positive direction'''
# Identify our current curvature map segment
mapSeg = self._getCurvatureMapSegment(p)
# get speed limit for the upcoming curvature map segment
nextMapSegSpeed = self._getCurvatureMapSpeedLimit(mapSeg + 1)
# get distance (in meters) from current position to start of next curvature map segment
nextMapSegDist = self._getDistToCurvatureMapSegmentEnd(p, mapSeg)
# set speed limit to the minimum of the current curvature map segment and the transition to the next curvature map segment speed
speedLimit = min(self._getCurvatureMapSpeedLimit(mapSeg),
self._speedCurve(nextMapSegDist,
nextMapSegSpeed)) # m/s
# loop through all remaining segments in that direction
for mapSeg in range(mapSeg + 1, self.curvatureMapNumSegments):
# increment distance by another curvature map segment length
nextMapSegDist += self.curvatureMapSegLengthM
# if that distance is greater than the distance it would take to stop, then break to save time (no need to look ahead any further)
if nextMapSegDist > self._maxLookAheadDist():
break
# get curvature map seg speed at this next segment
nextMapSegSpeed = self._getCurvatureMapSpeedLimit(
mapSeg + 1
) # NOTE: self.getCurvatureMapSpeedLimit(self.curvatureMapNumSegments) is 0
# limit us if the new map segment speed is slower than our current speed limit
speedLimit = min(speedLimit,
self._speedCurve(nextMapSegDist, nextMapSegSpeed))
# if targetP is ahead of currentP then check for a speed limit to slow down at the target
if self.targetP >= self.currentP:
speedLimit = min(
speedLimit,
self._speedCurve(
abs(self.targetP - self.currentP) *
self.spline.totalArcLength, 0))
return speedLimit
def _getNegSpeedLimit(self, p):
'''Returns speed limit for a requested arc length normalized parameter, p, moving in the negative direction'''
# Identify our current curvature map segment
mapSeg = self._getCurvatureMapSegment(p)
# get speed limit for the previous curvature map segment
prevMapSegSpeed = self._getCurvatureMapSpeedLimit(mapSeg - 1)
# get distance (in meters) from current position to start of previous curvature map segment
prevMapSegDist = self._getDistToCurvatureMapSegmentBegin(p, mapSeg)
# set speed limit to the minimum of the current curvature map segment and the transition to the previous curvature map segment speed
speedLimit = min(self._getCurvatureMapSpeedLimit(mapSeg),
self._speedCurve(prevMapSegDist,
prevMapSegSpeed)) # m/s
# loop through all remaining segments in that direction
for mapSeg in reversed(range(0, mapSeg)):
# increment distance by another curvature map segment length
prevMapSegDist += self.curvatureMapSegLengthM
# if that distance is greater than the distance it would take to stop, then break to save time (no need to look ahead any further)
if prevMapSegDist > self._maxLookAheadDist():
break
# get curvature map seg speed at this previous segment
prevMapSegSpeed = self._getCurvatureMapSpeedLimit(
mapSeg - 1) # NOTE: self.getCurvatureMapSpeedLimit(-1) is 0
# limit us if the new map segment speed is slower than our current speed limit
speedLimit = min(speedLimit,
self._speedCurve(prevMapSegDist, prevMapSegSpeed))
if self.targetP <= self.currentP:
speedLimit = min(
speedLimit,
self._speedCurve(
abs(self.targetP - self.currentP) *
self.spline.totalArcLength, 0))
return -speedLimit
class TestCatmullRom(unittest.TestCase):
def setUp(self):
self.spline = CatmullRom([
Vector3(0, 0, 0),
Vector3(1, 0, 0),
Vector3(2, 0, 0),
Vector3(3, 0, 0)
])
def testUpdateSplineCoefficientsError(self):
'''Tests that an error is raised if we call updateSplineCoefficients with an out of range segment'''
self.assertRaises(ValueError, self.spline.updateSplineCoefficients, 3)
def testPosition(self):
'''For an evenly spaced straight-line spline, test that position is traversed'''
seg = 0
u = 0
q = self.spline.position(seg, u)
self.assertEqual(q, Vector3(1.0, 0.0, 0.0))
u = 0.5
q = self.spline.position(seg, u)
self.assertEqual(q, Vector3(1.5, 0.0, 0.0))
u = 1.0
q = self.spline.position(seg, u)
self.assertEqual(q, Vector3(2.0, 0.0, 0.0))
def testVelocity(self):
'''For an evenly spaced straight-line spline, test that velocity is constant'''
seg = 0
u = 0
dq = self.spline.velocity(seg, u)
self.assertEqual(dq, Vector3(1.0, 0.0, 0.0))
u = 0.5
dq = self.spline.velocity(seg, u)
self.assertEqual(dq, Vector3(1.0, 0.0, 0.0))
u = 1.0
dq = self.spline.velocity(seg, u)
self.assertEqual(dq, Vector3(1.0, 0.0, 0.0))
def testAcceleration(self):
'''For an evenly spaced straight-line spline, test that acceleration is zero'''
seg = 0
u = 0
ddq = self.spline.acceleration(seg, u)
self.assertEqual(ddq, Vector3(0.0, 0.0, 0.0))
u = 0.5
ddq = self.spline.acceleration(seg, u)
self.assertEqual(ddq, Vector3(0.0, 0.0, 0.0))
u = 1.0
ddq = self.spline.acceleration(seg, u)
self.assertEqual(ddq, Vector3(0.0, 0.0, 0.0))
def testCurvature(self):
'''For an evenly spaced straight-line spline, test that curvature is zero'''
seg = 0
u = 0
curv = self.spline.curvature(seg, u)
self.assertEqual(curv, 0.0)
u = 0.5
curv = self.spline.curvature(seg, u)
self.assertEqual(curv, 0.0)
u = 1.0
curv = self.spline.curvature(seg, u)
self.assertEqual(curv, 0.0)