ST_AsEncodedPolyline
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Name

ST_AsEncodedPolyline — Returns an Encoded Polyline from a LineString geometry.

Synopsis

text ST_AsEncodedPolyline(geometry geom, integer precision=5);

Description

Returns the geometry as an Encoded Polyline. This format is used by Google Maps with precision=5 and by Open Source Routing Machine with precision=5 and 6.

Optional precision specifies how many decimal places will be preserved in Encoded Polyline. Value should be the same on encoding and decoding, or coordinates will be incorrect.

Availability: 2.2.0

Examples

Basic 

	SELECT ST_AsEncodedPolyline(GeomFromEWKT('SRID=4326;LINESTRING(-120.2 38.5,-120.95 40.7,-126.453 43.252)'));
	--result--
	|_p~iF~ps|U_ulLnnqC_mqNvxq`@

Use in conjunction with geography linestring and geography segmentize, and put on google maps

-- the SQL for Boston to San Francisco, segments every 100 KM
	SELECT ST_AsEncodedPolyline(
		ST_Segmentize(
			ST_GeogFromText('LINESTRING(-71.0519 42.4935,-122.4483 37.64)'),
				100000)::geometry) As encodedFlightPath;

javascript will look something like this where $ variable you replace with query result

<script type="text/javascript" src="http://maps.googleapis.com/maps/api/js?libraries=geometry"></script>
<script type="text/javascript">
	 flightPath = new google.maps.Polyline({
			path:  google.maps.geometry.encoding.decodePath("$encodedFlightPath"),
			map: map,
			strokeColor: '#0000CC',
			strokeOpacity: 1.0,
			strokeWeight: 4
		});
</script>