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A single message from topic:  Making sense of program code in Lazarus   in forum:  Off track
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Single message by Martin Wynne       Topic: Making sense of program code in Lazarus
Posted: 12 Dec 2020 09:24
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Martin Wynne
West Of The Severn, United Kingdom



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DerekStuart wrote: One of the things I was experimenting with before I temporarily gave up is importing GPS data from a database (simulating a tracker's output) and trying to plot it on a map. Have you ever tried anything like that before or is there anything you can suggest to point me in the right direction?
Hi Derek,

A popular format for recording GPS tracking data is in GPX files (*.gpx). There are lots of programs available for analysis, editing and plotting of GPX files.

GPX files are text-based, in XML format, so it's quite easy to parse and extract data from them in your own code.

More about the GPX format:

 https://www.topografix.com/gpx.asp

Details of the XML Schema for GPX:

 http://www.topografix.com/GPX/1/1/

Here's one of mine, opened in *Notepad++



trkpt is a single track point, and you can see it's easy to extract the latitude and longitude figures. I can post a bit of code showing how to do that if you wish?

Converting the lat and lon to X,Y co-ordinates for plotting on a screen map at different zoom levels is the tricky bit, involving some maths.

You can enter lat and lon directly in OSM to find the map location:




Note that for most of the UK, longitude is negative.

To get some GPX files to play with, click the GPS Traces link above.

*Notepad++ is the essential (free) text editor for programmers:

 https://notepad-plus-plus.org/

cheers,

Martin.


A single message from topic:  Making sense of program code in Lazarus   in forum:  Off track
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