Overlays and GeoJson

Hi Al,

I think both things are possible with Trackserver’s external file feature, although I haven’t tried drawing polygons, which would only be possible with KML files at this point.

If the data you have available is in GeoJSON, it would indeed seem unncessary to convert it to GPX or KML first, only to have Leaflet-Omnivore convert it back to GeoJSON.

Adding support of GeoJSON files shouldn’t be hard, since I think Leaflet-Omnivore can consume that without problems. It would come down to telling Trackserver about the file type and how to load it.

I’ll have a look to see how much work it is.

Regards,
Martijn.

Thanks Martijn, that would be great.

Just a quick answer, because I didn’t have mucht time to look into it.

It’s not very complicated, but there are one or two caveats to work around.

First, adding support for ‘geojson’ URLs is easy. Basically, you search the ‘class-trackserver.php’ file for occurrences of ‘kml’, and duplicate that code, replacing all instances of ‘kml’ with ‘geojson’:

Insert at 1109:
'geojson' => false,

Insert at 1278:

			if ( $atts['geojson'] ) {
				$urls = explode( ' ', $atts['geojson'] );
				$j    = 0;
				foreach ( $urls as $u ) {
					if ( ! empty( $u ) ) {
						$u        = $this->proxy_url( $u, $post_id );
						$tracks[] = array(
							'track_id'   => 'geojson' . $j,
							'track_url'  => $u,
							'track_type' => 'geojson',
							'style'      => $this->get_style(),
							'points'     => $this->get_points(),
							'markers'    => $this->get_markers(),
							'markersize' => $this->get_markersize(),
						);
						$j++;
					}
				}
			}

For the rest, Trackserver already knows how to display GeoJSON content, because it can use GeoJSON for internal tracks too.

First caveat: due to its internal use of GeoJSON, Trackserver expects the actual GeoJSON data to be wrapped in some Trackserver-specific construct, so the code must be changed for this use case. The simplest fix would be this:

In trackserver.js, on line 60, replace

return o.track;

with

            if (o.hasOwnProperty( 'track' )) {
                return o.track;
            }
            else {
                return o;
            }

With that in place, I was able to display the ‘majorincidents.json’ file using

[tsmap geojson=<url>]

It doesn’t seem to work with polygons, though. If your run into CORS restrictions loading JSON from an external domain, you may have to use Trackserver’s proxy feature.

There may be other issues. Please let me know how well this works.

Best regards,
Martijn.

Thanks very much for your help. I will fiddle with various options and let you know how I go, as (of course) its the polygons that i am most interested in – they show the fire extent, and i am trying to combine the last known positions of the trucks with where we believe the fire is, along with any new reports of fire extent that the trucks might upload.

So I have several options, either to convert the GeoJson to KML, which would also allow me to plot the extent on android devices (for example – Locus maps) or to export the location information from TrackServer and plot it on Google maps or similar.

Back to the drawing board, but there is at least one option that looks like it will work.

Thanks again for your help