From fcf40ec6a80e8e961250f63807172abdb0113cc8 Mon Sep 17 00:00:00 2001
From: Torsten Dreyer <Torsten@t3r.de>
Date: Mon, 31 Dec 2012 21:27:13 +0100
Subject: [PATCH] Autopilot: initialize the derivative filter

Dont let the derivative filter emit a spike on init or reset if the input
value is non-zero. This is a potential fix for #973.
---
 src/Autopilot/digitalfilter.cxx | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/Autopilot/digitalfilter.cxx b/src/Autopilot/digitalfilter.cxx
index 26377e131..adff0480a 100644
--- a/src/Autopilot/digitalfilter.cxx
+++ b/src/Autopilot/digitalfilter.cxx
@@ -75,6 +75,7 @@ class DerivativeFilterImplementation : public GainFilterImplementation {
 public:
   DerivativeFilterImplementation();
   double compute(  double dt, double input );
+  virtual void initialize( double output );
 };
 
 class ExponentialFilterImplementation : public GainFilterImplementation {
@@ -180,6 +181,12 @@ DerivativeFilterImplementation::DerivativeFilterImplementation() :
 {
 }
 
+void DerivativeFilterImplementation::initialize( double output )
+{
+  _input_1 = output;
+}
+
+
 bool DerivativeFilterImplementation::configure( const std::string & nodeName, SGPropertyNode_ptr configNode )
 {
   if( GainFilterImplementation::configure( nodeName, configNode ) )
-- 
2.39.5