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refactor: Refactor target direction logic in KF/CKF (#2539)
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Not sure what the use case for this was but to me it seems like the target propagation logic is flawed in KF/CKF. If we propagate to target from the last state the smoothing seems unnecessary. Also since the target surface is a perigee surface for us there are edge cases where the last state has a smaller "distance" to the perigee than the first one.

In general I'd say the user should take such a decision but this is too big of a change at the moment.

discovered with #2518
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@andiwand
andiwand committed Oct 19, 2023
1 parent 25331d0 commit fd80ca7
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Showing 4 changed files with 97 additions and 24 deletions.
57 changes: 47 additions & 10 deletions Core/include/Acts/TrackFinding/CombinatorialKalmanFilter.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -47,6 +47,16 @@

namespace Acts {

enum class CombinatorialKalmanFilterTargetSurfaceStrategy {
/// Use the first trackstate to reach target surface
first,
/// Use the last trackstate to reach target surface
last,
/// Use the first or last trackstate to reach target surface depending on the
/// distance
firstOrLast,
};

/// Track quality summary for one trajectory.
///
/// This could be used to decide if a track is to be recorded when the
Expand Down Expand Up @@ -200,6 +210,11 @@ struct CombinatorialKalmanFilterOptions {
/// The smoothing target surface
const Surface* smoothingTargetSurface = nullptr;

/// Strategy to propagate to reference surface
CombinatorialKalmanFilterTargetSurfaceStrategy
smoothingTargetSurfaceStrategy =
CombinatorialKalmanFilterTargetSurfaceStrategy::firstOrLast;

/// Whether to consider multiple scattering.
bool multipleScattering = true;

Expand Down Expand Up @@ -334,6 +349,11 @@ class CombinatorialKalmanFilter {
/// The smoothing target surface
const Surface* smoothingTargetSurface = nullptr;

/// Strategy to propagate to reference surface
CombinatorialKalmanFilterTargetSurfaceStrategy
smoothingTargetSurfaceStrategy =
CombinatorialKalmanFilterTargetSurfaceStrategy::firstOrLast;

/// Whether to consider multiple scattering.
bool multipleScattering = true;

Expand Down Expand Up @@ -1183,6 +1203,7 @@ class CombinatorialKalmanFilter {
// Screen output for debugging
ACTS_VERBOSE("Apply smoothing on " << nStates
<< " filtered track states.");

// Smooth the track states
auto smoothRes =
m_extensions.smoother(state.geoContext, *result.fittedStates,
Expand All @@ -1197,8 +1218,7 @@ class CombinatorialKalmanFilter {
return Result<void>::success();
}

// Obtain the smoothed parameters at first/last measurement state.
// The first state can also be a material state
// Obtain the smoothed parameters at first/last measurement state
auto firstCreatedState =
result.fittedStates->getTrackState(firstStateIndex);
auto lastCreatedMeasurement =
Expand All @@ -1214,7 +1234,8 @@ class CombinatorialKalmanFilter {
.closest();
};

// The smoothed free params at the first/last measurement state
// The smoothed free params at the first/last measurement state.
// (the first state can also be a material state)
auto firstParams = MultiTrajectoryHelpers::freeSmoothed(
state.options.geoContext, firstCreatedState);
auto lastParams = MultiTrajectoryHelpers::freeSmoothed(
Expand All @@ -1225,18 +1246,31 @@ class CombinatorialKalmanFilter {
const auto lastIntersection = target(lastParams);

// Update the stepping parameters - in order to progress to destination.
// At the same time, reverse navigation direction for further
// stepping if necessary.
// At the same time, reverse navigation direction for further stepping if
// necessary.
// @note The stepping parameters is updated to the smoothed parameters at
// either the first measurement state or the last measurement state. It
// assumes the target surface is not within the first and the last
// smoothed measurement state. Also, whether the intersection is on
// surface is not checked here.
bool closerToFirstCreatedState =
std::abs(firstIntersection.pathLength()) <=
std::abs(lastIntersection.pathLength());
bool useFirstTrackState = true;
switch (smoothingTargetSurfaceStrategy) {
case CombinatorialKalmanFilterTargetSurfaceStrategy::first:
useFirstTrackState = true;
break;
case CombinatorialKalmanFilterTargetSurfaceStrategy::last:
useFirstTrackState = false;
break;
case CombinatorialKalmanFilterTargetSurfaceStrategy::firstOrLast:
useFirstTrackState = std::abs(firstIntersection.pathLength()) <=
std::abs(lastIntersection.pathLength());
break;
default:
ACTS_ERROR("Unknown target surface strategy");
return KalmanFitterError::SmoothFailed;
}
bool reverseDirection = false;
if (closerToFirstCreatedState) {
if (useFirstTrackState) {
stepper.resetState(state.stepping, firstCreatedState.smoothed(),
firstCreatedState.smoothedCovariance(),
firstCreatedState.referenceSurface(),
Expand All @@ -1256,9 +1290,10 @@ class CombinatorialKalmanFilter {
"target surface");
state.options.direction = state.options.direction.invert();
}
const auto& surface = closerToFirstCreatedState
const auto& surface = useFirstTrackState
? firstCreatedState.referenceSurface()
: lastCreatedMeasurement.referenceSurface();

ACTS_VERBOSE(
"Smoothing successful, updating stepping state to smoothed "
"parameters at surface "
Expand Down Expand Up @@ -1374,6 +1409,8 @@ class CombinatorialKalmanFilter {
propOptions.actionList.template get<CombinatorialKalmanFilterActor>();
combKalmanActor.filterTargetSurface = tfOptions.filterTargetSurface;
combKalmanActor.smoothingTargetSurface = tfOptions.smoothingTargetSurface;
combKalmanActor.smoothingTargetSurfaceStrategy =
tfOptions.smoothingTargetSurfaceStrategy;
combKalmanActor.multipleScattering = tfOptions.multipleScattering;
combKalmanActor.energyLoss = tfOptions.energyLoss;
combKalmanActor.smoothing = tfOptions.smoothing;
Expand Down
53 changes: 42 additions & 11 deletions Core/include/Acts/TrackFitting/KalmanFitter.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -46,6 +46,16 @@

namespace Acts {

enum class KalmanFitterTargetSurfaceStrategy {
/// Use the first trackstate to reach target surface
first,
/// Use the last trackstate to reach target surface
last,
/// Use the first or last trackstate to reach target surface depending on the
/// distance
firstOrLast,
};

/// Extension struct which holds delegates to customise the KF behavior
template <typename traj_t>
struct KalmanFitterExtensions {
Expand Down Expand Up @@ -157,6 +167,10 @@ struct KalmanFitterOptions {
/// The reference Surface
const Surface* referenceSurface = nullptr;

/// Strategy to propagate to reference surface
KalmanFitterTargetSurfaceStrategy referenceSurfaceStrategy =
KalmanFitterTargetSurfaceStrategy::firstOrLast;

/// Whether to consider multiple scattering
bool multipleScattering = true;

Expand Down Expand Up @@ -293,6 +307,10 @@ class KalmanFitter {
/// The target surface
const Surface* targetSurface = nullptr;

/// Strategy to propagate to target surface
KalmanFitterTargetSurfaceStrategy targetSurfaceStrategy =
KalmanFitterTargetSurfaceStrategy::firstOrLast;

/// Allows retrieving measurements for a surface
const std::map<GeometryIdentifier, SourceLink>* inputMeasurements = nullptr;

Expand Down Expand Up @@ -916,10 +934,8 @@ class KalmanFitter {
return KalmanFitterError::SmoothFailed;
}
// Screen output for debugging
if (logger().doPrint(Logging::VERBOSE)) {
ACTS_VERBOSE("Apply smoothing on " << nStates
<< " filtered track states.");
}
ACTS_VERBOSE("Apply smoothing on " << nStates
<< " filtered track states.");

// Smooth the track states
auto smoothRes =
Expand Down Expand Up @@ -963,18 +979,31 @@ class KalmanFitter {
const auto lastIntersection = target(lastParams);

// Update the stepping parameters - in order to progress to destination.
// At the same time, reverse navigation direction for further
// stepping if necessary.
// At the same time, reverse navigation direction for further stepping if
// necessary.
// @note The stepping parameters is updated to the smoothed parameters at
// either the first measurement state or the last measurement state. It
// assumes the target surface is not within the first and the last
// smoothed measurement state. Also, whether the intersection is on
// surface is not checked here.
bool closerToFirstCreatedState =
std::abs(firstIntersection.pathLength()) <=
std::abs(lastIntersection.pathLength());
bool useFirstTrackState = true;
switch (targetSurfaceStrategy) {
case KalmanFitterTargetSurfaceStrategy::first:
useFirstTrackState = true;
break;
case KalmanFitterTargetSurfaceStrategy::last:
useFirstTrackState = false;
break;
case KalmanFitterTargetSurfaceStrategy::firstOrLast:
useFirstTrackState = std::abs(firstIntersection.pathLength()) <=
std::abs(lastIntersection.pathLength());
break;
default:
ACTS_ERROR("Unknown target surface strategy");
return KalmanFitterError::SmoothFailed;
}
bool reverseDirection = false;
if (closerToFirstCreatedState) {
if (useFirstTrackState) {
stepper.resetState(state.stepping, firstCreatedState.smoothed(),
firstCreatedState.smoothedCovariance(),
firstCreatedState.referenceSurface(),
Expand All @@ -994,9 +1023,10 @@ class KalmanFitter {
"target surface");
state.options.direction = state.options.direction.invert();
}
const auto& surface = closerToFirstCreatedState
const auto& surface = useFirstTrackState
? firstCreatedState.referenceSurface()
: lastCreatedMeasurement.referenceSurface();

ACTS_VERBOSE(
"Smoothing successful, updating stepping state to smoothed "
"parameters at surface "
Expand Down Expand Up @@ -1230,6 +1260,7 @@ class KalmanFitter {
auto& kalmanActor = kalmanOptions.actionList.template get<KalmanActor>();
kalmanActor.inputMeasurements = &inputMeasurements;
kalmanActor.targetSurface = kfOptions.referenceSurface;
kalmanActor.targetSurfaceStrategy = kfOptions.referenceSurfaceStrategy;
kalmanActor.multipleScattering = kfOptions.multipleScattering;
kalmanActor.energyLoss = kfOptions.energyLoss;
kalmanActor.reversedFiltering = kfOptions.reversedFiltering;
Expand Down
3 changes: 3 additions & 0 deletions Examples/Algorithms/TrackFinding/src/TrackFindingAlgorithm.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -17,6 +17,7 @@
#include "Acts/Propagator/Propagator.hpp"
#include "Acts/Surfaces/PerigeeSurface.hpp"
#include "Acts/Surfaces/Surface.hpp"
#include "Acts/TrackFinding/CombinatorialKalmanFilter.hpp"
#include "Acts/TrackFitting/GainMatrixSmoother.hpp"
#include "Acts/TrackFitting/GainMatrixUpdater.hpp"
#include "Acts/TrackFitting/KalmanFitter.hpp"
Expand Down Expand Up @@ -115,6 +116,8 @@ ActsExamples::ProcessCode ActsExamples::TrackFindingAlgorithm::execute(
ActsExamples::TrackFindingAlgorithm::TrackFinderOptions options(
ctx.geoContext, ctx.magFieldContext, ctx.calibContext, slAccessorDelegate,
extensions, pOptions, pSurface.get());
options.smoothingTargetSurfaceStrategy =
Acts::CombinatorialKalmanFilterTargetSurfaceStrategy::first;

// Perform the track finding for all initial parameters
ACTS_DEBUG("Invoke track finding with " << initialParameters.size()
Expand Down
8 changes: 5 additions & 3 deletions Examples/Algorithms/TrackFitting/src/KalmanFitterFunction.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -81,13 +81,13 @@ struct KalmanFitterFunctionImpl final : public TrackFitterFunction {
bool energyLoss = false;
Acts::FreeToBoundCorrection freeToBoundCorrection;

IndexSourceLink::SurfaceAccessor m_slSurfaceAccessor;
IndexSourceLink::SurfaceAccessor slSurfaceAccessor;

KalmanFitterFunctionImpl(Fitter&& f, DirectFitter&& df,
const Acts::TrackingGeometry& trkGeo)
: fitter(std::move(f)),
directFitter(std::move(df)),
m_slSurfaceAccessor{trkGeo} {}
slSurfaceAccessor{trkGeo} {}

template <typename calibrator_t>
auto makeKfOptions(const GeneralFitterOptions& options,
Expand All @@ -107,14 +107,16 @@ struct KalmanFitterFunctionImpl final : public TrackFitterFunction {
options.geoContext, options.magFieldContext, options.calibrationContext,
extensions, options.propOptions, &(*options.referenceSurface));

kfOptions.referenceSurfaceStrategy =
Acts::KalmanFitterTargetSurfaceStrategy::first;
kfOptions.multipleScattering = multipleScattering;
kfOptions.energyLoss = energyLoss;
kfOptions.freeToBoundCorrection = freeToBoundCorrection;
kfOptions.extensions.calibrator.connect<&calibrator_t::calibrate>(
&calibrator);
kfOptions.extensions.surfaceAccessor
.connect<&IndexSourceLink::SurfaceAccessor::operator()>(
&m_slSurfaceAccessor);
&slSurfaceAccessor);

return kfOptions;
}
Expand Down

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