Index: sodar/trunk/sodar/data.py
===================================================================
--- sodar/trunk/sodar/data.py (revision 65)
+++ sodar/trunk/sodar/data.py (revision 66)
@@ -59,5 +59,5 @@
 
 import re
-
+import numpy as n
 
 class Data(list):
@@ -75,4 +75,5 @@
                      [sample.strip() for sample in data.split('$')]
                      if sample.strip()])
+        self._normalize()
 
     def __getitem__(self, index):
@@ -107,4 +108,44 @@
         raise IndexError('Data index out of range')
 
+    def _normalize(self):
+        """Clean up data for analysis."""
+        self._copy()
+        # self._convert()
+        # compute time interval
+        # correct for missing times
+        # compute minium altitude
+        # compute maximum overall altitude
+        # compute number of altitudes
+        # compute altitude interval
+        # correct for missing altitudes
+        # mark maximum altitude with good values for each sample
+        # mark minimum altitude with invalid values for each sample
+        # convert direction to radians
+        # compute u,v,c components
+        # compute colorspecs
+        # compute plotting parameters
+    
+    def _copy(self):
+        """Create a deep copy of all the samples in this Data instance."""
+        self.samples = [(dict(sample.header), list(sample.body))
+                        for sample in self]
+        for sample in self.samples:
+            for altitude in sample[1]:
+                altitude = dict(altitude)
+    
+    def _convert(self):
+        """Convert to numbers and correct for invalid values."""
+        INVALID = "-9999"
+        # convert to numbers and correct for invalid values
+        for sample in self.samples:
+            for altitude in sample[1]:
+                for key in altitude.keys():
+                    try:
+                        if altitude[key] == INVALID:
+                            raise ValueError
+                        altitude[key] = float(altitude[key])
+                    except (ValueError, TypeError, KeyError):
+                        altitude[key] = n.NaN
+
 
 class Sample(object):