在查詢時，可以利用軌跡或幾何類型的外包矩形框來輔助查詢。例如下圖就是一條在x,y,t空間中的運(yùn)動的軌跡和它對應(yīng)的外包矩形框。

在Ganos Trajectory模塊中，使用BoxNDF類型表示外包框。對于軌跡、幾何類型，可以求得其外包框，也可以提取其在特定時間段的子外包框。

• 提取幾何類型的外包框，也可以在外包框上附加時間范圍（2000-01-01 00:00:10至02:13:20）。

  WITH geom AS(
      SELECT ('POLYGON((12.7243236691148 4.35238368367118,12.9102992732078 1.49748113937676,12.5926592946053 1.67643963359296' ||
              ',12.0197574747333 3.19258554889152,12.7243236691148 4.35238368367118))')::geometry a )
  SELECT ST_MakeBox(a),ST_MakeBox(a,'2000-01-01 00:00:10'::timestamp, '2000-01-01 02:13:20'::timestamp) from geom;

• 提取軌跡類型的外包框，也可以提取軌跡在限定時間內(nèi)的子軌跡的外包框。

  With traj AS (
      Select ST_makeTrajectory(
          'STPOINT', 
          'LINESTRING(0 0, 50 50, 100 100)'::geometry,
          tsrange('2000-01-01 00:00:00'::timestamp, '2000-01-01 00:01:40'::timestamp),
          '{"leafcount":3,
              "attributes":{
                  "velocity": {"type": "integer","length": 2,"nullable" : true,"value": [120,130,140]}, 
                  "accuracy": {"type": "float", "length": 4, "nullable" : false,"value": [120,130,140]}, 
                  "bearing": {"type": "float", "length": 8, "nullable" : false,"value": [120,130,140]}, 
                  "acceleration": {"type": "string", "length": 20, "nullable" : true,"value": ["120","130","140"]},
                  "active": {"type": "timestamp","nullable" : false,"value": ["Fri Jan 01 11:35:00 2010", "Fri Jan 01 12:35:00 2010", "Fri Jan 01 13:30:00 2010"]}
              }, "events": [{"2" : "Fri Jan 02 15:00:00 2010"}, {"3" : "Fri Jan 02 15:30:00 2010"}]
            }') a )
  SELECT ST_MakeBox(a), ST_MakeBox(a,'1999-12-31 23:00:00'::timestamp, '2000-01-01 00:00:30'::timestamp) from traj;

在較為復(fù)雜的應(yīng)用場景中，對軌跡的處理時常分為兩步：

1. 根據(jù)軌跡的外包框信息過濾掉大部分的無關(guān)數(shù)據(jù)。

2. 對剩余的數(shù)據(jù)進(jìn)行精細(xì)處理。

可以假設(shè)和查詢軌跡相似的軌跡必然與查詢軌跡的外包框相交，或是距離在一定范圍內(nèi)，然后只計(jì)算符合條件的軌跡和查詢之間的相似度，得到一個近似的結(jié)果。

• 外包框相交：

  -- 將軌跡SRID統(tǒng)一設(shè)置為4326
  UPDATE trajectory_table SET traj = ST_SetSRID(traj,4326) WHERE ST_SRID(traj)!=4326;
  
  With query AS (
    SELECT '{"trajectory":{"version":1,"type":"STPOINT","leafcount":3,"start_time":"2020-04-11 17:42:30","end_time":"2020-04-11 17:45:00","spatial":"SRID=4326;LINESTRING(114.35 39.28 4,114.36 39.28 4,114.35 39.29 4)","timeline":["2020-04-11 17:42:30","2020-04-11 17:43:30","2020-04-11 17:45:00"],"attributes":{"leafcount":3,"intensity":{"type":"integer","length":4,"nullable":true,"value":[80,30,50]}}}}'::trajectory q)
  SELECT ST_lcsDistance(traj, q, 500), trajectory_table.* FROM trajectory_table, query WHERE traj && q ORDER BY ST_lcsDistance(traj, q, 500);

• 外包框空間距離小于500米，時間距離小于1小時：

  -- 將軌跡SRID統(tǒng)一設(shè)置為4326
  UPDATE trajectory_table SET traj = ST_SetSRID(traj,4326) WHERE ST_SRID(traj)!=4326;
  
  With query AS (
    SELECT '{"trajectory":{"version":1,"type":"STPOINT","leafcount":3,"start_time":"2020-04-11 17:42:30","end_time":"2020-04-11 17:45:00","spatial":"SRID=4326;LINESTRING(114.35 39.28 4,114.36 39.28 4,114.35 39.29 4)","timeline":["2020-04-11 17:42:30","2020-04-11 17:43:30","2020-04-11 17:45:00"],"attributes":{"leafcount":3,"intensity":{"type":"integer","length":4,"nullable":true,"value":[80,30,50]}}}}'::trajectory q)
  SELECT ST_lcsDistance(traj, q, 500), trajectory_table.* FROM trajectory_table, query WHERE traj && ST_ExpandTemporal(ST_ExpandSpatial(ST_MakeBox(q), 500/110000), 3600) ORDER BY ST_lcsDistance(traj, q, 500);

  說明

  • 由于對軌跡調(diào)用ST_Buffer函數(shù)時無法使用traj列的索引，因此必須擴(kuò)展q，將q的外包框擴(kuò)大相應(yīng)距離。

  • 由于軌跡使用經(jīng)緯度坐標(biāo)，需要先將500米轉(zhuǎn)為經(jīng)緯度范圍，一經(jīng)緯度大約110km。一小時為3600秒。

常用外包框相交算子：