As I’ve mentioned before, I love data. The more of it there is, the more fun it
is to dig into. And I also have a deep passion for programming. Recently I
started building an app with Dart + Flutter + Material Design 3 and fell in
love with the language. The experience is very similar to what I felt when I
first played with Kotlin — an incredibly engaging and beautiful language from
JetBrains.
For example, I really liked type extensions. It’s a mind-blowing feature for a
PHP developer. I’d desperately want something like this in PHP:
extension Temperature on double{
static const double kelvinOffset = 273.15;
double asTemperature(int degreesUnit) {
return 0 == degreesUnit ? toCelsius : toFahrenheit;
}
double get toCelsius => this - kelvinOffset;
double get toFahrenheit => toCelsius * (9/5) + 32;
}
import 'package:weather/extension/temperature.dart';
final double temp = weather!.temperatureNow.asTemperature(degreesUnit);
But let’s get to the point: Dart is not only a JIT language, it’s also a
compiled one. I really liked that flexibility, so I decided to write my first
CLI script for converting KML to GPX. For some reason, none of the free
online tools could produce a valid GPX that Garmin Connect would accept — it
kept throwing a parsing error. So I set aside one evening, opened the docs, and
in less than an hour wrote my first working Dart program that can be easily run
from the command line. It looks like this:
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| String convertKmlToGpx(XmlDocument kml, {required bool verbose}) {
final name = kml.xpath('/kml/Document/name').first.innerText;
final track = kml.xpath('/kml/Document/Folder/Placemark');
final date = DateFormat('y-M-dTH:m:s').parse(track
.map((node) => node.findElements('TimeStamp').first.findElements('when'))
.first
.single
.innerText
.toString());
final builder = XmlBuilder();
builder.processing('xml', 'version="1.0" encoding="UTF-8"');
builder.element('gpx', nest: () {
builder.attribute('creator', 'enuage');
builder.attribute('version', version);
builder.attribute('xsi:schemaLocation', 'http://www.topografix.com/GPX/1/1 http://www.topografix.com/GPX/11.xsd');
builder.attribute('xmlns', 'http://www.topografix.com/GPX/1/1');
builder.attribute('xmlns:xsi', 'http://www.w3.org/2001/XMLSchema-instance');
builder.attribute('xmlns:ns2', 'http://www.garmin.com/xmlschemas/GpxExtensions/v3');
builder.element('metadata', nest: () {
builder.element('time', nest: '${date.toIso8601String()}Z');
});
builder.element('trk', nest: () {
builder.element('name', nest: name);
builder.element('trkseg', nest: () {
for (var node in track) {
final when = node
.findElements('TimeStamp')
.firstOrNull
?.findElements('when')
.firstOrNull
?.innerText
.trim();
final coordinates = node
.findElements('Point')
.firstOrNull
?.findElements('coordinates')
.firstOrNull
?.innerText
.trim();
if (when == null || coordinates == null) continue;
final parts = coordinates.split(',');
if (parts.length < 2) continue;
final longitude = double.tryParse(parts[0].trim());
final latitude = double.tryParse(parts[1].trim());
if (longitude == null || latitude == null) continue;
final elevationM = parts.length > 2 ? double.tryParse(parts[2].trim()) : null;
// final elevationF = elevationM != null ? elevationM * 3.28084 : null;
builder.element(
'trkpt',
attributes: {'lat': '$latitude', 'lon': '$longitude'},
nest: () {
if (elevationM != null) {
final eleStr = elevationM == elevationM.truncateToDouble()
? elevationM.toInt().toString()
: '$elevationM';
builder.element('ele', nest: () => builder.text(eleStr));
}
builder.element('time', nest: () => builder.text(
'${DateFormat('y-M-dTH:m:s+00:00').parse(when).toIso8601String()}Z'
));
},
);
}
});
});
});
return builder.buildDocument().toXmlString(pretty: true);
}
|
The script worked on the first try, parsed perfectly by Garmin Connect, and you
can view the activity interactively:
