Logging¶

FollowPath publishes a rich set of internal state through four pluggable static logging consumers. Wire them to your logger of choice (AdvantageKit, WPILog, SmartDashboard, etc.) once, and every FollowPath command run emits telemetry.

All four consumers default to no-op, so logging is zero-cost until you opt in.

Wiring¶

Register all four at robot init. For AdvantageKit, a one-liner per consumer is typical:

import edu.wpi.first.math.Pair;
import edu.wpi.first.math.geometry.Pose2d;
import edu.wpi.first.math.geometry.Translation2d;
import frc.robot.lib.BLine.FollowPath;
import org.littletonrobotics.junction.Logger;

FollowPath.setDoubleLoggingConsumer(
    p -> Logger.recordOutput(p.getFirst(), p.getSecond()));
FollowPath.setBooleanLoggingConsumer(
    p -> Logger.recordOutput(p.getFirst(), p.getSecond()));
FollowPath.setPoseLoggingConsumer(
    p -> Logger.recordOutput(p.getFirst(), p.getSecond()));
FollowPath.setTranslationListLoggingConsumer(
    p -> Logger.recordOutput(p.getFirst(), p.getSecond()));

For plain NetworkTables:

FollowPath.setDoubleLoggingConsumer(p -> NetworkTableInstance.getDefault()
    .getTable("FollowPath").getEntry(keyTail(p.getFirst())).setDouble(p.getSecond()));
// ... similar for the others

Consumers are set on the FollowPath class, not the command

In the very first releases, examples showed consumers being passed to FollowPath.Builder. They moved to static setters on FollowPath itself (etherex clarified this early on the Chief Delphi thread). There is no per-command override — all running FollowPath instances share the same consumers.

Published keys¶

All keys are prefixed with FollowPath/.

Double¶

Key	Units	Meaning
`FollowPath/dtSeconds`	s	Time delta between successive `execute()` calls.
`FollowPath/remainingPathDistanceMeters`	m	Remaining straight-line path distance from robot to end.
`FollowPath/currentSegmentLengthMeters`	m	Length of the current translation segment.
`FollowPath/currentSegmentProgress`	0–1	Robot's projection progress along the current segment.
`FollowPath/translationElementIndex`	—	Current translation cursor index.
`FollowPath/rotationElementIndex`	—	Current rotation cursor index (−1 when inactive).
`FollowPath/rotationPreviousElementIndex`	—	Last completed rotation target index.
`FollowPath/translationControllerOutput`	m/s	Clamped output of the translation PID.
`FollowPath/crossTrackControllerOutput`	m/s	CTE PID output (unclamped).
`FollowPath/crossTrackError`	m	Signed cross-track error (`+` = right of path).
`FollowPath/rotationControllerOutput`	rad/s	Rotation PID output.
`FollowPath/targetRotationDeg`	deg	Current rotation setpoint sent to the rotation PID.
`FollowPath/rotationErrorDeg`	deg	Shortest-angle heading error.
`FollowPath/currentRotationTargetInitRad`	rad	Heading at the start of the active rotation segment (for profile interpolation).
`FollowPath/segmentProgress`	0–1	Progress used for the rotation profile.
`FollowPath/translationHandoffFromIndex` / `...ToIndex`	—	Emitted on each handoff cycle.
`FollowPath/eventTriggerElementIndex`	—	Current event-trigger walk cursor.
`FollowPath/eventTriggersFiredCount`	—	Number of triggers fired so far in this run.

Boolean¶

Key	Meaning
`FollowPath/finished`	True when `isFinished()` returns true.
`FollowPath/finishedIsLastRotationElement`	True when rotation cursor is past the last rotation target.
`FollowPath/finishedIsLastTranslationElement`	True when translation cursor is on the last translation element.
`FollowPath/finishedTranslationAtSetpoint`	True when translation PID reports at-setpoint (remaining distance within end tolerance).
`FollowPath/finishedRotationAtSetpoint`	True when heading is within end rotation tolerance.
`FollowPath/translationHandoffOccurred`	True on the cycle a translation handoff happened.
`FollowPath/currentSegmentDegenerate`	True if the current segment is effectively zero-length.
`FollowPath/rotationHasActiveTarget`	True when a rotation target is currently being tracked.
`FollowPath/useTRatioBasedTranslationHandoffs`	Echoes the builder setting for the current run.

Pose¶

Key	Meaning
`FollowPath/closestPoint`	Closest point on the current segment to the robot, packaged as a `Pose2d` with the robot's heading.
`FollowPath/rotationTargetPose`	Where the active rotation target lives on the segment (translation on the segment line + the target heading).

Translation2d[]¶

Key	Meaning
`FollowPath/pathTranslations`	All translation targets in order. Emitted once at `initialize()`.
`FollowPath/robotTranslations`	Robot position samples collected during the run. Sampled every 3rd `execute()` cycle, capped at the most recent 300 samples.

Viewing in AdvantageScope¶

With AdvantageKit wired to the consumers above, the keys appear under NT:/AdvantageKit/RealOutputs/FollowPath/.... Three useful visualizations:

Robot trail. Drop FollowPath/robotTranslations onto the 2D/3D field viewer to see the actual traversed path as a trail.
Path outline. Drop FollowPath/pathTranslations onto the same field viewer for the nominal path.
Remaining distance curve. Chart FollowPath/remainingPathDistanceMeters over time — a clean monotonic decay is what you want to see. Oscillations near the end are a PID tuning signal.

When debugging, a screenshot of the remaining-distance graph is typically the single most useful piece of evidence. (Etherex asked for exactly this on the Chief Delphi thread more than once.)

Testing tips¶

Log FollowPath/translationHandoffOccurred + index keys to spot unexpected handoffs or stalls.
Log FollowPath/currentSegmentDegenerate when debugging zero-length-segment bugs (which were fixed in v0.8.0 but a useful sanity-check signal).
Log FollowPath/crossTrackError during CTE tuning — under-tuned will show sustained error, over-tuned will show oscillation.
Log FollowPath/rotationErrorDeg during rotation tuning to spot overshoot / oscillation at the endpoint.

Disabling logging¶

Pass null to any setter to restore the no-op. Recommended in a competition build if you're logging a lot and want to cut NT/log volume:

FollowPath.setDoubleLoggingConsumer(null);  // reverts to no-op

Or be selective — keep boolean + pose keys, skip the high-frequency double keys.