altoslib: Use a longer filter for descent values

This makes descent speeds almost useful, a huge improvement

Signed-off-by: Keith Packard <keithp@keithp.com>

1 files changed, 6 insertions, 3 deletions

diff --git a/altoslib/AltosState.java b/altoslib/AltosState.java
index a120e0c7..8eacf975 100644
--- a/altoslib/AltosState.java
+++ b/altoslib/AltosState.java
@@ -31,8 +31,9 @@ public class AltosState implements Cloneable, Serializable {
 
 	public int set;
 
+	static final double filter_len = 2.0;
 	static final double ascent_filter_len = 0.5;
-	static final double descent_filter_len = 0.5;
+	static final double descent_filter_len = 5.0;
 
 	/* derived data */
 
@@ -64,8 +65,10 @@ public class AltosState implements Cloneable, Serializable {
 		}
 
 		void set_filtered(double new_value, double time) {
-			if (prev_value != AltosLib.MISSING)
-				new_value = (prev_value * 15.0 + new_value) / 16.0;
+			if (prev_value != AltosLib.MISSING) {
+				double f = 1/Math.exp((time - prev_set_time) / filter_le);
+				new_value = f * new_value + (1-f) * prev_value;
+			}
 			set(new_value, time);
 		}