GPXIN-6: Distance calculations

Re-Opening as have found a use-case for this (received an email which appears to be asking if it's possible)

Still a little concerned about the processing overhead, but I think the work-around is to have it disabled by default and to expose a method which will allow it to be enabled (GPXIN-17).

GPXIN-17 has been implemented, so this functionality can now be implemented as an experimental feature

As noted in the design notes (see Links section), the experimental key for this functionality is calcDistance

Basic calculations have been implemented (though currently only tested with one dataset). Example usage is

<?php
require_once('GPXIngest.class.php');
$gpx = new GPXIngest();
$gpx->loadFile('gpxtestfile.gpx');
$gpx->enableExperimental('calcDistance');
$gpx->ingest();
$tpts = $gpx->getTrackPointNames('journey0','seg0');
print_r($gpx->getTrackPoint('journey0','seg0',$tpts[3]));
print_r($gpx->getTrackPoint('journey0','seg0',$tpts[4]));

The returned distance travelled was then calculated manually and using online calculators. Looks like the calculations are correct.

Commit 0312b20 refers.

Still need to push the distance out to an array of some form so that stats can be used/updated for each Segment/Track.

If the functionality is not enabled, the method calculateTravelledDistance will return _0_ which might get confusing somewhere down the line - it's probably worth having a list of which experimental features are enabled pushed to the metadata (have raised GPXIN-18 for implementation).

Commit ea35449 pushes the distance travelled to the stats objects, example implementation

<?php
require_once('GPXIngest.class.php');
$gpx = new GPXIngest();

$gpx->loadFile('testgpx.gpx');
$gpx->enableExperimental('calcDistance');
$gpx->ingest();
$tpts = $gpx->getTrackPointNames('journey0','seg0');

echo "\n\nJourney\n";
print_r($gpx->getJourneyStats());

echo "\n\nTracks\n";
print_r($gpx->getStats('journey0'));

echo "\n\nSegment\n";
print_r($gpx->getStats('journey0','seg0'));

echo "\n\nTrackpoints\n";
print_r($gpx->getTrackPoint('journey0','seg0',$tpts[4]));
print_r($gpx->getTrackPoint('journey0','seg0',$tpts[5]));

It also incorporates a minor bugfix - when the location hadn't moved, the distance calculations were returning NAN. Have added a check so that 0 is returned in this instance.

Needs further testing, but does appear to be working correctly.

The resources required for the calculations aren't as high as originally expected either, so once stable and tested, this can be moved out of experimental features.

An issue with the processing was raised on Github (https://github.com/bentasker/PHP-GPX-Ingest/issues/2) and fixed on 19 Jan.

Other than that, seems to work OK so closing FR.