python-osm: osmhistory

osmhistory.py is a tool that can retrieve object data from the OpenStreetMap API at a given timestamp.

The current OSM API supports the download of the current version of an object (e.g. a relation) with a single API call or over the JOSM remote control. 
http://www.openstreetmap.org/api/0.6/relation/21628/full

OSM-history can do the same but at any given timestamp. Thus you can get OSM-objects from a month ago, one year ago, or just the day before something bad happened with the osm objects. 
./osmhistory.py -r 21628 -t 2009-10-01 -o relation_21628_2009-10-01.osm

The command retrieves the relation 21628 at the timestamp 2009-10-01 and writes the output to the file relation_21628_2009-10-01.osm.

In order to do that the script first searches (with a binary search) the matching version of the given OSM object. Then it collects all objects that are referenced by this object. e.g. a relation references other relations, ways and/or nodes. A way references nodes.

All that objects are downloaded by the script, too. An example output of the script with the executed API calls looks like this: 
bisect:relation21628
 bisect:/api/0.6/relations?relations=21628
 bisect:/api/0.6/relation/21628/4
 bisect:/api/0.6/relation/21628/6
 bisect:/api/0.6/relation/21628/5
bisect:way8022736
 bisect:/api/0.6/ways?ways=8022736
 bisect:/api/0.6/way/8022736/4
 bisect:/api/0.6/way/8022736/6
 bisect:/api/0.6/way/8022736/7
bisect:way19736185
 bisect:/api/0.6/ways?ways=19736185
[....]
bisect:node59975181
 bisect:/api/0.6/nodes?nodes=59975181
bisect:node362803235
 bisect:/api/0.6/nodes?nodes=362803235
 bisect:/api/0.6/node/362803235/4
 bisect:/api/0.6/node/362803235/2
 bisect:/api/0.6/node/362803235/3
bisect:node500348455
 bisect:/api/0.6/nodes?nodes=500348455
[...]

After retrieving the history, you can compare the current version of the object and the historic version. You can load the two versions into different layers with JOSM.
new version in front of the old version old version in front of the current version, zoomed in

As you can see on the left picture, the route of the relation has been changed. On the right picture, you can see the moved roundabout.

Revert the changes (experimental, not much tested)

The historic version of the osm objects are prepared to revert the current osm object versions. To achieve this: If you delete that tag, the you get exactly the historic object. JOSM will add an action=modify attribute and the version attribute gets incremented. The reverted object will be uploaded with the next commit.

Example of the historic osm file: 
<node uid="110263" timestamp="2009-09-18T15:12:19Z" lon="9.5154672" visible="true" version="4" user="werner2101" lat="47.6790064" id="362803252">
  <tag k="osmhistory:old_version_date" v="2_2009-10-01"></tag>
</node>
<way uid="110263" timestamp="2009-09-18T15:12:22Z" visible="true" version="17" user="werner2101" id="4675294">
  <nd ref="29691653"></nd>
  <nd ref="362606768"></nd>
[...]
  <tag k="maxspeed" v="50"></tag>
  <tag k="ref" v="K 7726"></tag>
  <tag k="highway" v="tertiary"></tag>
  <tag k="osmhistory:old_version_date" v="16_2009-10-01"></tag>
</way>
<relation uid="110263" timestamp="2009-09-18T15:12:23Z" visible="true" version="7" user="werner2101" id="21628">
  <member ref="4675294" role="" type="way"></member>
  <member ref="8022729" role="" type="way"></member>
  <member ref="8022735" role="" type="way"></member>
[...]
  <tag k="operator" v="Bodenseekreis"></tag>
  <tag k="type" v="route"></tag>
  <tag k="route" v="road"></tag>
  <tag k="ref" v="K 7726"></tag>
  <tag k="osmhistory:old_version_date" v="5_2009-10-01"></tag>
</relation>

Integration into OSM API

The current python implementation of that tool needs lots of api calls. Even if I could download more than one object of the current objects, the download and the binary search of older objects still produces lots of api calls. I'm not sure how long it would take to download large relations like the boundary of a country.

If other osm users think that the tool is usefull, it's functionality should be included into the OSM api (which is written using Ruby on Rails).

Werner Hoch
Last modified: Tue Dec 29 12:27:50 CET 2009