From 520d762382eab783f081440f1f5bb61fec3583cb Mon Sep 17 00:00:00 2001
From: Andrew Tridgell <tridge@samba.org>
Date: Fri, 6 Jul 2012 15:04:54 +1000
Subject: [PATCH] Filter: split the DerivativeFilter steps into update() and
 slope()

this allows us to apply new data at a different rate than we calculate
the slope.
---
 libraries/Filter/DerivativeFilter.cpp | 20 ++++++++++++++------
 libraries/Filter/DerivativeFilter.h   |  7 +++++--
 2 files changed, 19 insertions(+), 8 deletions(-)

diff --git a/libraries/Filter/DerivativeFilter.cpp b/libraries/Filter/DerivativeFilter.cpp
index 4a796f9b32..817bd0a64f 100644
--- a/libraries/Filter/DerivativeFilter.cpp
+++ b/libraries/Filter/DerivativeFilter.cpp
@@ -16,15 +16,20 @@
 #include <DerivativeFilter.h>
 
 template <class T,  uint8_t FILTER_SIZE>
-float DerivativeFilter<T,FILTER_SIZE>::apply(T sample, uint32_t timestamp)
+void DerivativeFilter<T,FILTER_SIZE>::update(T sample, uint32_t timestamp)
 {
-	float result = 0;
-
     // add timestamp before we apply to FilterWithBuffer
     _timestamps[FilterWithBuffer<T,FILTER_SIZE>::sample_index] = timestamp;
 
 	// call parent's apply function to get the sample into the array
 	FilterWithBuffer<T,FILTER_SIZE>::apply(sample);
+}
+
+
+template <class T,  uint8_t FILTER_SIZE>
+float DerivativeFilter<T,FILTER_SIZE>::slope(void)
+{
+	float result = 0;
 
     // use f() to make the code match the maths a bit better. Note
     // that unlike an average filter, we care about the order of the elements
@@ -81,13 +86,16 @@ void DerivativeFilter<T,FILTER_SIZE>::reset(void)
 }
 
 // add new instances as needed here
-template float DerivativeFilter<float,5>::apply(float sample, uint32_t timestamp);
+template void DerivativeFilter<float,5>::update(float sample, uint32_t timestamp);
+template float DerivativeFilter<float,5>::slope(void);
 template void DerivativeFilter<float,5>::reset(void);
 
-template float DerivativeFilter<float,7>::apply(float sample, uint32_t timestamp);
+template void DerivativeFilter<float,7>::update(float sample, uint32_t timestamp);
+template float DerivativeFilter<float,7>::slope(void);
 template void DerivativeFilter<float,7>::reset(void);
 
-template float DerivativeFilter<float,9>::apply(float sample, uint32_t timestamp);
+template void DerivativeFilter<float,9>::update(float sample, uint32_t timestamp);
+template float DerivativeFilter<float,9>::slope(void);
 template void DerivativeFilter<float,9>::reset(void);
 
 
diff --git a/libraries/Filter/DerivativeFilter.h b/libraries/Filter/DerivativeFilter.h
index 5a6ce1171e..1267a9ba8b 100644
--- a/libraries/Filter/DerivativeFilter.h
+++ b/libraries/Filter/DerivativeFilter.h
@@ -26,8 +26,11 @@ class DerivativeFilter : public FilterWithBuffer<T,FILTER_SIZE>
 	// constructor
 	DerivativeFilter() : FilterWithBuffer<T,FILTER_SIZE>() {};
 
-	// apply - Add a new raw value to the filter, retrieve the filtered result
-	virtual float apply(T sample, uint32_t timestamp);
+	// update - Add a new raw value to the filter, but don't recalculate
+	virtual void update(T sample, uint32_t timestamp);
+
+	// return the derivative value
+	virtual float slope(void);
 
 	// reset - clear the filter
 	virtual void reset();