XML Newbie Woes

[Graham Samuel]

I have been asked to do some work on some GPX files: these files originate from GPS devices, and are in XML format. I've never had to deal with XML before, so I have been trying to learn how to do so from the LC user manual - from about page 189.  There is a sample XML file and a discussion of the various 'revXML' functions which are on offer. There are a few typos, but it doesn't **look** hard.
(I don't have any other source of information since my crazy ISP has cut off my internet connection, and I am confined at present to emails sent & received via a friend.)

So far, so good: however, although I can create an XML tree and retrieve the Root Node as per the documentation, I can't make any of the other functions work on my data. I hope someone can explain the fundamentals of what I'm doing wrong.

My GPX file begins like this:

<?xml version="1.0" encoding="UTF-8"?>
<gpx xmlns="http://www.topografix.com/GPX/1/1" creator="Geolives" 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">
  <metadata />
  <trk>
    <trkseg>
      <trkpt lat="42.78981" lon="1.336446">
        <ele>750.5912</ele>
      </trkpt>
      <trkpt lat="42.78981" lon="1.336446">
        <ele>750.5912</ele>
      </trkpt>
[etc etc etc]

The file seems to be well-formed, apart from the fact that the first child node is found by revXML to be "gpx/metadata", and I can't see the closure for the metadata tag at the other end of the document. In fact the document ends </gpx>f I try to stick in </metadata> before this last line, the LC function refuses to form the table, so the original file must be right. I don't understand this.

Anyway, revXMLRootNode returns "gpx" (without the quotes)

and revXMLFirstChild returns "/gpx/metadata"

but after that nothing works. However closely I follow the example in the manual, I can't get the revXMLContents or revXMLNodeContents functions to return anything. For example (among many attempts), revXMLNodeContents(1,"/gpx/metadata/trk/trkseg") returns

"xmlerr, can't find element"

I feel like I've tried everything, but it seems there's something basic I haven't grasped. XML seems like a simple idea, but in practice it's dreadfully easy to slip up.

TIA for any advice, as long as it doesn't mean significant downloading.

Graham


Sent from my iPad