From 59070969a9e7e7d83342de2655a3e947ea0f8585 Mon Sep 17 00:00:00 2001
From: Ian Jackson <ian@liberator.relativity.greenend.org.uk>
Date: Sat, 8 Jan 2011 19:14:55 +0000
Subject: [PATCH] detpic/display-nmra: new NmraAssist::HighPassFilter for more
 reliable capture of data from track

---
 detpic/NmraAssist.pm        | 43 +++++++++++++++++++++++++++++++++++++
 detpic/display-nmra         |  9 ++++++--
 detpic/display-nmra-decoded |  8 ++++++-
 3 files changed, 57 insertions(+), 3 deletions(-)
 create mode 100644 detpic/NmraAssist.pm

diff --git a/detpic/NmraAssist.pm b/detpic/NmraAssist.pm
new file mode 100644
index 0000000..94c36e2
--- /dev/null
+++ b/detpic/NmraAssist.pm
@@ -0,0 +1,43 @@
+# -*- perl -*-
+
+package NmraAssist;
+
+BEGIN {
+    use Exporter ();
+    our ($VERSION, @ISA, @EXPORT, @EXPORT_OK, %EXPORT_TAGS);
+    $VERSION     = 1.00;
+    @ISA         = qw(Exporter);
+    @EXPORT      = qw();
+    %EXPORT_TAGS = ( );
+
+    @EXPORT_OK   = qw();
+}
+
+package NmraAssist::HighPassFilter;
+
+# We subtract an alpha-smoothed value
+our $default_timeconstant= 300e-6; # seconds, e-life
+
+sub new ($) {
+    my ($class) = @_;
+    my $sf= {
+	SmoothedValue => 0,
+	TimeConstant => $default_timeconstant,
+	LastSampleTime => 0
+    };
+    bless $sf, $class;
+    return $sf;
+}
+
+sub transform ($$$) {
+    my ($sf, $t, $value) = @_;
+
+    my $interval= $t - $sf->{LastSampleTime};
+    $sf->{SmoothedValue} *= exp( -$interval / $sf->{TimeConstant} );
+    $sf->{SmoothedValue} += $value * $interval / $sf->{TimeConstant};
+    $sf->{LastSampleTime}= $t;
+    $value -= $sf->{SmoothedValue};
+    return $value;
+}
+
+1;
diff --git a/detpic/display-nmra b/detpic/display-nmra
index 2941e8a..bbd9a96 100755
--- a/detpic/display-nmra
+++ b/detpic/display-nmra
@@ -3,10 +3,14 @@ set -ex
 
 xpixels=1024
 ypixels=768
-ypersamp=8
-fsd=0.3
+ypersamp=20
+fsd=1.0
 
 perl -e <t.nmra.dat '
+	use NmraAssist;
+
+	$filter= NmraAssist::HighPassFilter->new();
+
 	for (;;) {
 		@l= ();
 		$ticks= "";
@@ -18,6 +22,7 @@ perl -e <t.nmra.dat '
 			next if m/^\;/;
 			m/^\s*([-e0-9.]+)\s+([-0-9.]+)\s*$/ or die;
 			($t,$samp)=($1,$2);
+			$samp= $filter->transform($t, $samp);
 			$h= sprintf "%d",
 				($samp/(2.0*'$fsd') + 0.5) * ('$ypersamp'-1);
 			for ($y=0, $l=0; $y<'$ypersamp'; $y+=2, $l++) {
diff --git a/detpic/display-nmra-decoded b/detpic/display-nmra-decoded
index 3ca18fb..e2b2654 100755
--- a/detpic/display-nmra-decoded
+++ b/detpic/display-nmra-decoded
@@ -36,6 +36,7 @@
 
 use strict qw(vars refs);
 use IO::Handle;
+use NmraAssist;
 
 sub usec_from_to ($$) {
     my ($from,$to) = @_; # uses $from->{S}, $from->{U}, $to->{S}, $to->{U}
@@ -244,6 +245,8 @@ sub found_datapoint ($$) {
 
 #---------- datapoint reader ----------
 
+our $filter= NmraAssist::HighPassFilter->new();
+
 sub read_stdin() {
     reset_bit_decoder();
 
@@ -251,7 +254,10 @@ sub read_stdin() {
 	last if STDIN->eof;
 	next if m/^\;/;
 	m/^\s*([-.0-9e]+)\s+([-.0-9e]+)\s*$/ or die "$_ ?";
-	found_datapoint($1 * 1e6, $2);
+	my ($t, $value) = ($1,$2);
+	$value= $filter->transform($t, $value);
+	$t *= 1e6;
+	found_datapoint($t, $value);
     }
     die $! if STDIN->error;
 }
-- 
2.30.2