gpsprof with altitude works again on garmin GPS 18USB.

NaN is problematic in Python, use PosInf instead until isnan is in the
standard Python library.

2 files changed, 10 insertions, 3 deletions

diff --git a/gps.py b/gps.py
index ad934adb..cc2583cd 100755
--- a/gps.py
+++ b/gps.py
@@ -9,8 +9,15 @@ from math import *
 # PEP 75 (http://python.fyxm.net/peps/pep-0754.html).
 # This includes at least versions up to 2.3.4.
 PosInf = 1e300000
-NaN = PosInf/PosInf
-def isnan(x): return x == NaN
+# NaN = PosInf/PosInf
+# IEEE754 says NaN == NaN is always false!
+# so this is wrong: 
+#    def isnan(x): return x == NaN
+
+# so let's use PosInf as a proxy
+# this is not mathmetically correct but good enough for altitude
+NaN = PosInf
+def isnan(x): return x > 1e300000
 
 ONLINE_SET	= 0x00000001
 TIME_SET	= 0x00000002
diff --git a/gpsprof b/gpsprof
index 67095663..2f3b32b4 100755
--- a/gpsprof
+++ b/gpsprof
@@ -121,7 +121,7 @@ class spaceplot:
         fmt += 'plot cx(t, cep),cy(t, cep) title "CEP (50%%) = %f meters",  ' % (cep_meters)
         fmt += ' "-" using 1:2 with points ls 3 title "%d GPS fixes" ' % (len(self.fixes))
         if not gps.isnan(alt_avg):
-            fmt += ', "-" using ( %f ):($5 != NaN ? $5 - %f : Inf) axes x1y2 with points ls 2 title " %d Altitude fixes, Average = %f" \n' % (lon_max +1, alt_avg, alt_num, alt_avg)
+            fmt += ', "-" using ( %f ):($5 < 100000 ? $5 - %f : Inf) axes x1y2 with points ls 2 title " %d Altitude fixes, Average = %f" \n' % (lon_max +1, alt_avg, alt_num, alt_avg)
         else:
             fmt += "\n"
         fmt += self.header(session)