Wednesday, July 1, 2015

Road so far

As GSOC's mid-term is closing in, I thought I'd share what's been done so far! In case you haven't seen my earlier posts, here's a quick reminder on what I'm working on: implementing an Open Street Map (OSM) editor for Marble that allows the user to import ".osm" files, edit them with OSM-specific tools, and finally export them into ready-for-upload files. All that inside Marble's existing Annotate Plugin ( editor for ".kml" maps ).

What's been done so far?  

As one would imagine, OSM( ) has noticeable differences from KML ( ), the schema upon which Marble is built. These differences, from an OSM perspective, mainly consist in server-generated data such as id, changeset, timestamp etc. but also in core data elements, such as the <relation> and <tag> tags.

Up until now, I've developed a way to store this server-generated data, mainly by saving it
as KML's  ExtendedData. Exporting to ".osm" files is now possible as well, so that pretty much makes Marble a KML-to-OSM ( and in reverse )  translator at the moment ( it has some draw backs of course )

What was the main challenge?
Not everything can be translated perfectly from OSM to KML and vice-versa, so while translating, I had to ensure as little data as possible is lost.

Since data parsing isn't a really picture-worthy topic, here is an example of a map's journey through Marble's editor:

The OSM version of a highway: "sample highway"
<?xml version="1.0" encoding="UTF-8"?>
<osm version="0.6" generator="Marble 0.21.23 (0.22 development version)">
    <node lat="-23.7082750358" lon="-4.4577696853" id="-1" action="modify" visible="false"/>
    <node lat="-21.0946495732" lon="-11.9900406335" id="-2" action="modify" visible="false"/>
    <node lat="-16.6010784801" lon="-6.7785258299" id="-3" action="modify" visible="true">
        <tag k="name" v="sample placemark"/>
    <way id="-75891" action="modify" visible="true">
        <tag k="name" v="sample highway"/>
        <tag k="highway" v="residential"/>
        <nd ref="-1"/>
        <nd ref="-2"/>

The KML version of it after going through Marble's editor: The osm data( that is irrelevant from a KML perspective ) is stored within an ExtendedData block
            <name>sample highway</name>
            <ExtendedData xmlns:osm_data="Marble/temporary/namespace">
                <osm_data:OsmDataSnippet id="-75891" visible="true">
                        <osm_data:tag k="highway" v="residential"/>
                        <osm_data:nd count="0">
                            <osm_data:OsmDataSnippet id="-1" visible="false" action="modify"/>
                        <osm_data:nd count="1">
                            <osm_data:OsmDataSnippet id="-2" visible="false" action="modify"/>
                <coordinates>-4.457769,-23.708275 -11.990040,-21.094649</coordinates>

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