diff -r dfefb6003498 -r c55e1f2a4db4 igc.cc
--- a/igc.cc	Sun Jan 29 00:38:40 2012 +0100
+++ b/igc.cc	Sun Jan 29 01:51:02 2012 +0100
@@ -1,5 +1,51 @@
 #include "igc.h"
 
+Fix::Fix(const QString &s)
+{
+    int pos = 0;
+
+    time_ = QTime::fromString(s.mid(pos, 6), "hhmmss"); 
+    pos += 6;	
+
+    gps_.lat = s.mid(pos, 8); pos += 8;	// DDMMmmm[NS]
+    gps_.lon = s.mid(pos, 9); pos += 9;	// DDDMMmmm[EW]
+
+    is3d_ = s.mid(pos, 1) == "A"; 
+    pos += 1;
+
+    alt_[baro] = s.mid(pos, 5).toInt(); pos += 5;
+    alt_[gps]  = s.mid(pos, 5).toInt(); pos += 5;
+}
+
+
+IGC::IGC()
+#ifdef __GXX_EXPERIMENTAL_CXX0X__
+    : altitude_({0})
+#endif
+{
+#ifndef __GXX_EXPERIMENTAL_CXX0X__
+    memset(altitude_, 0, sizeof(altitude_));
+#endif
+}
+
+IGC::IGC(QTextStream &s)
+#ifdef __GXX_EXPERIMENTAL_CXX0X__
+    : altitude_({0})
+#endif
+{
+#ifndef __GXX_EXPERIMENTAL_CXX0X__
+    memset(altitude_, 0, sizeof(altitude_));
+#endif
+    read(s);
+}
+
+IGC::~IGC()
+{
+    for (size_t i = 0; i < sizeof(altitude_)/sizeof(altitude_[0]); ++i) {
+	delete altitude_[i];
+    }
+}
+
 void IGC::read(QTextStream &in)
 {
     while (!in.atEnd()) {
@@ -37,19 +83,19 @@
     }
 }
 
-Fix::Fix(const QString &s)
+const QVector<QPointF>& IGC::altitude(Fix::Source src) const
 {
-    int pos = 0;
+   
+    // optimization: if already allocated, return the allocated vector
+    if (altitude_[src]) return *altitude_[src];
 
-    time_ = QTime::fromString(s.mid(pos, 6), "hhmmss"); 
-    pos += 6;	
+    altitude_[src] = new QVector<QPointF>;
 
-    gps_.lat = s.mid(pos, 8); pos += 8;	// DDMMmmm[NS]
-    gps_.lon = s.mid(pos, 9); pos += 9;	// DDDMMmmm[EW]
+    for (Fixes::const_iterator i = fixes_.begin();
+	     i != fixes_.end();
+	     i++) {
+	     *altitude_[src] << QPointF(QTime().secsTo(i->time()), i->altitude(src));
+    }
 
-    is3d_ = s.mid(pos, 1) == "A"; 
-    pos += 1;
-
-    alt_[baro] = s.mid(pos, 5).toInt(); pos += 5;
-    alt_[gps]  = s.mid(pos, 5).toInt(); pos += 5;
+    return *altitude_[src];
 }