Naive XML questions

[Graham Samuel]

I feel stupid, but even with Sarah Reichelt’s help, there are very very simple things I can’t do with the LC XML functions. My current problem is this:

I have a series of XML files which are in fact .gpx files - a collection of GPS coordinates representing a route on the Earth’s surface. There are thousands of files around which I can use as test data, so I don’t have to roll my own. Taking just one of these examples, I can do the following in LC

1. Get the user to find the file and download it

2. Check it’s a .gpx file

3. Turn it into an LC XML data structure with an integer ID

4. Find out how many child nodes there are.

Then it all goes wrong, because I don’t seem to be able to address the individual nodes. This is obviously needed for further progress, in functions like revXMLFirstChild  and revXMLNodeContents.

I just don’t know what format to use. Sarah’s tutorial doesn’t help because her data structure is too simplified.

If you’re still with me, this is what the beginning of a typical file looks like:

> <?xml version="1.0" encoding="UTF-8"?>
> <gpx xmlns="http://www.topografix.com/GPX/1/1" creator="Digital Crow" version="1.0" 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="43.319729" lon="2.128369">
> <ele>169.623637</ele> </trkpt>

> <trkpt lat="43.319731" lon="2.128375">
> <ele>169.744722</ele> </trkpt>

> <trkpt lat="43.319731" lon="2.128375">
> <ele>169.744722</ele> </trkpt>

> <trkpt lat="43.319731" lon="2.128388">
> <ele>169.266626</ele> </trkpt>
> 
etc - there may sometimes be thousands of these “trkpt” elements.

So, suppose I want to get the first instance of the “lon” attribute into a local variable. How do I address the first <trk> node etc in order to do it? I have attempted various common-sense methods, but none work.

This must be child’s play to a lot of people, just not me.

Hoping for some guidance.

Graham