From c507e143aac0bc251b02bbe3c812bf81b7026ff7 Mon Sep 17 00:00:00 2001
From: Keith Packard <keithp@keithp.com>
Date: Sat, 17 Oct 2020 15:29:11 -0700
Subject: [PATCH] altoslib: Clip accelerometer-based speed to >= 0

Negative vertical speeds computed by axial acceleration aren't
sensible, so just clip them to zero so that plots are more useful.

Signed-off-by: Keith Packard <keithp@keithp.com>
---
 altoslib/AltosFlightSeries.java |  6 +++++-
 altoslib/AltosTimeSeries.java   | 10 ++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/altoslib/AltosFlightSeries.java b/altoslib/AltosFlightSeries.java
index 38256f0e..d9d59f1b 100644
--- a/altoslib/AltosFlightSeries.java
+++ b/altoslib/AltosFlightSeries.java
@@ -348,8 +348,12 @@ public class AltosFlightSeries extends AltosDataListener {
 			else
 				accel_series.integrate(temp_series);
 
+			AltosTimeSeries clip_series = make_series(speed_name, AltosConvert.speed);
+
+			temp_series.clip(clip_series, 0, Double.POSITIVE_INFINITY);
+
 			accel_speed_series = make_series(speed_name, AltosConvert.speed);
-			temp_series.filter(accel_speed_series, 0.1);
+			clip_series.filter(accel_speed_series, 0.1);
 		}
 
 		if (alt_speed_series != null && accel_speed_series != null) {
diff --git a/altoslib/AltosTimeSeries.java b/altoslib/AltosTimeSeries.java
index 80720f15..d12fbe70 100644
--- a/altoslib/AltosTimeSeries.java
+++ b/altoslib/AltosTimeSeries.java
@@ -342,6 +342,16 @@ public class AltosTimeSeries implements Iterable<AltosTimeValue>, Comparable<Alt
 		return f;
 	}
 
+	public AltosTimeSeries clip(AltosTimeSeries clip, double min, double max) {
+		for (AltosTimeValue v: values) {
+			double value = v.value;
+			if (value < min) value = min;
+			if (value > max) value = max;
+			clip.add(v.time, value);
+		}
+		return clip;
+	}
+
 	public AltosTimeSeries(String label, AltosUnits units) {
 		this.label = label;
 		this.units = units;
-- 
2.30.2