xml, xpath,postgres 9.1

Hello everybody, sorry for my english.
I need to extract the xml: lat, lon and ele.  The xml I have it save on a
table (gpx.object_value). For the first two works for me:

SELECT (xpath ('//lat ', gpx.object_value)) [i] FROM gpx
SELECT (xpath ('//lon ', gpx.object_value)) [i] FROM gpx

My question is how do <ele> ? Probe of everything:
'./trk/trkseg/trkpt/ele/text()'
'//ele'
'//ele/text()'
'//*[//ele]'

Please,help me.
TKANKS

Information:
postgres(postgis),eclipse,jsp

INSERT INTO gpx(object_name, object_value) VALUES ('t1.gpx',
cast(pg_read_file('t1.gpx', 0, 1000000) As xml));

Document xml:
- <gpx xmlns="http://www.topografix.com/GPX/1/1" creator="MapMyTracks"
version="1.1" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.topografix.com/GPX/1/1
http://www.topografix.com/GPX/1/1/gpx.xsd">
- <trk>
- <trkseg>
- <trkpt lat="12.645648333" lon="-7.884185">
<ele>20.2</ele>
<time>2007-12-30T08:27:03Z</time>
</trkpt>
- <trkpt lat .......

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