Permanent ID: Unterschied zwischen den Versionen

Version vom 11. April 2019, 22:29 Uhr

This is an unofficial proposal for a "permanent ID" (osm_pid) for OpenStreetMap (OSM).

See https://wiki.openstreetmap.org/wiki/Permanent_ID for a more official state of discussions.

The goal is to get an opaque fixed length ASCII string. And that are the design considerations:

• The OSM id alone is not stable enough (as probably most agree); and it can represent many concepts (and that's by design in OSM).
• The version no. of the object is needed which makes clear which tags are (or have been) referred to.
• Coordinates are needed, because a change of the way and area geometries does not increment the version number.

So a stable Permanent ID could have the following form (which leads to a fixed length string of 35 chars in total):

 [N|W|R]<osm_id>#<version>[+|-]<lon>[+|-]<lat>

where:

• N,W,R stands for Node, Way, or Relation.
• osm_id is left-padded with zeros to get 10 chars ("digits").
• version is 4 digits left padded with zeros.
• coordinates have 5 fixed decimal places (lat is 2 and lon is 3 digits wide, both are signed and left-padded with zeros).

Example: "Schloss Kyburg" (Castle Kyburg) has relation 1169711, version #5 at coordinates 47.4584, 8.74343 which becomes following Permanent ID:

 osm_pid = R0001169711#0005+47.45840+008.74343

Service: In order to be really useful, a service should be implemented, which returns most recent Permanent ID even if a an object has been changed (thus having another Permanent ID).

Alternative Encodings

Same "triple" values as above (osm type/id, version and coordinates) but with different encodings:

Use OSM ID number (big integer 64 bit) together with OSM type (Node, Way, Relation)

• either with preceeding N,W,R as string.
• or as integer (32 bit) with following formula: osm_id = <node id> × 10 (eg. 123 → 1230), osm_id = (<way id> × 10) + 1 (eg. 123 → 1231), osm_id (<relation id> × 10) + 4 (eg. 123 → 1234). (Source: Mapbox, see [1]).

Additionally (optionally) for validation:

• use and store version (small integer 16 bit)
• use and store Latitude and Longitude (as centroid from line and polygons) as signed integers (32 bit) with a scale factor of 1e7, so an integer Latitude of -412870685 equates to -41.2870685 (as the original OSM database schema in "Rails port"), in order to retain a stable reference.

Example: "Schloss Kyburg" having relation id 1169711 with version 5 at coordinates 47.4584, 8.74343 (see also above) becomes following Instant ID:

 osm_pid2 = 11697114 plus osm_version = 5, osm_lat = 474584000, osm_lon = 87434300