tile.proto

syntax = "proto2";
option optimize_for = LITE_RUNTIME;
package opentraffic.osmlr;

import "segment.proto";

// traffic tile consists of a list of entries, where each entry is either a
// Segment or a marker indicating that the traffic segment is no longer in use.
// the ID of a particular traffic segment within the tile is its offset in the
// list.
//
// the reason for including markers for deleted segments (sometimes called
// "tombstones" in the literature) is so that tiles can have continuity across
// data updates. traffic segments which have been updated in a way which is
// compatible across previous versions (i.e: map-matching returns the same road
// segments to some tolerance) will retain their IDs. anything which has changed
// too much will have the old ID marked deleted and a new ID assigned.
//
// assigning IDs therefore potentially requires looking at all previous graphs,
// and a single "master" process to assign new IDs without conflicts. since we
// anticipate data updates to be rare events (monthly, quarterly, etc...) then
// this should not be a problem. in return, we get (mostly) compact IDs which
// are (mostly) tolerant to data updates.
//

message MarkedDeleted {
  optional uint32 segment_deleted_date = 1;

  // TODO - possible add information about segments that replace the deleted
  // segment
}

message Tile {

  message Entry {
    // an entry in the tile should be _either_ a Segment _or_ a Marker. a tile
    // containing an Entry with both or neither is invalid.
    // Date is when the OSMLR segment was created (if segment exists) or the
    // date when the segment was deleted (if marker exists)
    optional Segment segment = 1;
    optional MarkedDeleted marker = 2;
    optional uint32 segment_creation_date = 3;
  }

  // a tile consists of a list of Entries.
  repeated Entry entries = 1;

  // Creation date and time (UTC epoch seconds) for this OSMLR tile.
  optional uint32 creation_date = 2;

  // Reference to the OSM changeset Id. While not an exact representation of
  // the state of the OSM planet file that OSMLR was derived from, this
  // provides context on age and provenance of tile data derived from OSM.
  optional uint64 changeset_id = 3;
  
  // A string meant to describe this tile. It may be used to describe the geographic
  // extents of the tile but has no strict format. So as to remain projection
  // or really tiling system agnostic, its simple string which can be interpreted
  // differently depending on the tiling system used to generate and consume the tile
  optional string description = 4;
}