Help: SQL to select closest points within groups of records grouped by time

Question

Hi,
I need help to find an SQL for efficient solution for the following problem:
- I have 20 buses circling on one bus route and their locations are reported every 10 seconds and recorded into a spatial table “bus_location” with “bus_loc” as SDO_GEOMETRY type.
- Each bus location record there has a msg_datetime column with the time when the location was recorded.
- Buses circle the bus route 8-12 times, from A to B, then from B back to A, then new loop from A to B, and so on.
- I have 3 timing points in spatial table “timing_point” with “tp_loc” as SDO_GEOMETRY type.
- A bus will pass each timing point 8-12 times in one direction and 8-12 times in the other direction, while making loops on the bus route.
My task is: for each timing point, for each bus, for each trip direction (A-B or B-A), find the closest bus location to that timing point.
Example:
Bus...*TimingPoint*......*Time*.....*Distance*
...........................................*between*
...........................................*bus and TP*
12......A................14:01:00......250 m
12......A................14:01:10......150 m
12......A................14:01:20......12 m <== This is the record closest to the TP for this pass
12......A................14:01:30......48 m
12......A................14:01:40......100 m
12......A................14:01:50......248 m
12......A................14:29:40......122 m
12......A................14:29:50......72 m
12......A................14:30:00......9 m <== This is the record closest to the TP for this pass
12......A................14:30:10......10 m
12......A................14:30:20......12 m
I tried to use SDO_NN and I can get closest bus locations, but how to find the closest bus location for each pass? Or how to identify a groups of bus locations which are together within 2-3 minutes and to find closest record for each of these groups of locations?
Thank you very much for any help.
Milan
Edited by: mburazor on 9-Feb-2012 2:41 PM

Answer 1

Milan,
Yes, the problem is one of analytics not spatial. Here is another go that should be independent of year/month/date/hour/minute
as it does all its math based on an absolute number of minutes since 1970. I round to 5 minutes but you could round/trunc to any
particular interval (5 minutes, 10 minutes, 15 minutes etc)
Note that I have created extra records in the same table that I built. (Tip: good idea to provide a sample dataset to the forum when
asking difficult SQL questions like this.)
drop table buslocns;
create table buslocns(
busno number,
timingpt varchar2(1),
pttime   timestamp,
distance number)
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:00','YYYY/MM/DD HH24:MI:SS'),250);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:10','YYYY/MM/DD HH24:MI:SS'),150);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:20','YYYY/MM/DD HH24:MI:SS'),12);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:30','YYYY/MM/DD HH24:MI:SS'),48);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:40','YYYY/MM/DD HH24:MI:SS'),100);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:01:50','YYYY/MM/DD HH24:MI:SS'),248);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:29:40','YYYY/MM/DD HH24:MI:SS'),122);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:29:50','YYYY/MM/DD HH24:MI:SS'),72);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:30:00','YYYY/MM/DD HH24:MI:SS'),9);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:30:10','YYYY/MM/DD HH24:MI:SS'),10);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:30:20','YYYY/MM/DD HH24:MI:SS'),12);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:59:40','YYYY/MM/DD HH24:MI:SS'),53);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:59:50','YYYY/MM/DD HH24:MI:SS'),28);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 15:00:00','YYYY/MM/DD HH24:MI:SS'),12);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 15:00:10','YYYY/MM/DD HH24:MI:SS'),73);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:44:40','YYYY/MM/DD HH24:MI:SS'),53);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 14:44:50','YYYY/MM/DD HH24:MI:SS'),28);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 15:45:00','YYYY/MM/DD HH24:MI:SS'),12);
insert into buslocns values (12,'A',to_timestamp('2012/02/10 15:45:10','YYYY/MM/DD HH24:MI:SS'),73);
commit;
with tensOfMinutes as (
select row_number() over (order by busno,timingpt, pttime) as rid,
       busno,
       timingpt,
       pttime,
       round(((cast(pttime as date) - cast('01-JAN-1970' as date)) * 1440) / 5) * 5 as mins,
       distance
  from BUSLOCNS
select busno,timingpt,to_char(to_date('01-JAN-1970','DD-MON-YYYY') + ( mins / 1440 ),'DD-MON-YYYY HH24:MI:SS') as pttime,minDist
  from (select busno,timingpt,mins,min(distance) as minDist
          from tensOfMinutes a
         group by a.busno, a.timingpt, a.mins
         order by 1, 2, 3 ) ;
-- Result
BUSNO                  TIMINGPT PTTIME               MINDIST
12                     A        10-FEB-2012 14:00:00 12
12                     A        10-FEB-2012 14:30:00 9
12                     A        10-FEB-2012 14:45:00 28
12                     A        10-FEB-2012 15:00:00 12
12                     A        10-FEB-2012 15:45:00 12regards
Simon