Refactor overpass support using own implementation of overpass layer.

assets/osmtogeojson/README.md

@@ -0,0 +1,89 @@
+osmtogeojson
+============
+
+Converts [OSM](http://openstreetmap.org) [data](http://wiki.openstreetmap.org/wiki/OSM_XML) to [GeoJSON](http://www.geojson.org/). Try the [demo](http://tyrasd.github.io/osmtogeojson/)!
+
+* stable
+* real OSM [polygon detection](https://wiki.openstreetmap.org/wiki/Overpass_turbo/Polygon_Features)
+* proper OSM multipolygon support
+* full support for extended Overpass API [geometry modes](http://wiki.openstreetmap.org/wiki/Overpass_API/Overpass_QL#Print_.28out.29)
+* well [tested](https://github.com/tyrasd/osmtogeojson/tree/gh-pages/test/) and proven
+* fast
+
+This code is used in and maintained by the [overpass turbo](http://github.com/tyrasd/overpass-ide) project.
+
+[![Build Status](https://secure.travis-ci.org/tyrasd/osmtogeojson.png)](https://travis-ci.org/tyrasd/osmtogeojson)
+
+Usage
+-----
+
+### command line tool
+  
+Installation:
+
+      $ npm install -g osmtogeojson
+
+Usage:
+
+    $ osmtogeojson file.osm > file.geojson
+
+Supported command line options are shown with:
+
+    $ osmtogeojson --help
+
+When working with extra large data files (≳ 100 MB) it is recommended to run the programm with a little extra memory to avoid *process out of memory* errors. The easiest way to do this is by running the command as `node <path-to-osmtogeojson>` and setting the `--max_old_space_size=…` parameter to the available memory size in MB (osmtogeojson typically needs about 4-5 times the input data size):
+
+    $ node --max_old_space_size=8192 `which osmtogeojson` large.osm > large.geojson
+
+### nodejs library
+
+Installation:
+
+    $ npm install osmtogeojson
+
+Usage:
+
+    var osmtogeojson = require('osmtogeojson');
+    osmtogeojson(osm_data);
+
+### browser library
+
+    <script src='osmtogeojson.js'></script>
+
+    osmtogeojson(osm_data);
+
+API
+---
+
+### `osmtogeojson( data, options )`
+
+Converts OSM data into GeoJSON.
+
+* `data`: the OSM data. Either as a XML DOM or in [OSM JSON](http://overpass-api.de/output_formats.html#json).
+* `options`: optional. The following options can be used:
+  * `flatProperties`: If true, the resulting GeoJSON feature's properties will be a simple key-value list instead of a structured json object (with separate tags and metadata). default: false
+  * `uninterestingTags`: Either a [blacklist](https://github.com/tyrasd/osmtogeojson/blob/2.0.0/index.js#L14-L24) of tag keys or a callback function. Will be used to decide if a feature is *interesting* enough for its own GeoJSON feature.
+  * `polygonFeatures`: Either a [json object](https://github.com/tyrasd/osmtogeojson/blob/2.0.0/polygon_features.json) or callback function that is used to determine if a closed way should be treated as a Polygon or LineString. [read more](https://wiki.openstreetmap.org/wiki/Overpass_turbo/Polygon_Features)
+
+The result is a javascript object of GeoJSON data:
+
+GeoJSON
+-------
+
+The GeoJSON produced by this library will include exactly one GeoJSON-feature for each of the following OSM objects (that is everything that is also visible in overpass turbo's map view):
+
+* all unconnected or [*interesting*](#api) tagged nodes (POIs)
+* all ways (except [*uninteresting*](#api) multipolygon outlines)
+* all multipolygons (simple multipolygons with exactly one closed outer way are present via their outer way)
+
+All data is given as a FeatureCollection. Each Feature in the collection has an `id` property that is formed from the type and id of the original OSM object (e.g. `node/123`) and has the member `properties` containing the following data:
+
+* `type`: the OSM data type
+* `id`: the OSM id 
+* `tags`: a collection of all tags
+* `meta`: metainformaton about the feature (e.g. version, timestamp, user, etc.)
+* `relations`: an array of relations the feature is member of. Each relation is encoded as an object literal containing the following properties: `role` (membership role), `rel` (the relation's id) and `reltags` (contains all tags of the relation)
+* `tainted`: this flag is set when the feature's geometry is incomplete (e.g. missing nodes of a way or missing ways of a multipolygon)
+
+If the [option](#api) `flatProperties` is set to true, the `properties` object will not contain any nested object literals, but directly provide a concise id, meta data and the tags of the respective OSM object.
+