query to return hourly snapshot

I am look for help in developing a query that will return the nearest process record that was
logged at or after each hour in a day (i.e. hourly snapshot).


Below are typical sample data.  Also, I've included a query used to return the average of the
process value for each hour to give an example for the format that I am trying to achieve.

Thanks for the help.

Regards,

Richard

select * from process limit 10;
       tstamp        | process
---------------------+---------
 2005-10-25 21:10:41 | 3.56513
 2005-10-25 21:10:42 | 3.56503
 2005-10-25 21:10:43 | 3.56494
 2005-10-25 21:10:44 | 3.56484
 2005-10-25 21:10:45 | 3.56475
 2005-10-25 21:10:46 | 3.56465
 2005-10-25 21:10:47 | 3.56455
 2005-10-25 21:10:48 | 3.56446
 2005-10-25 21:10:49 | 3.56436
 2005-10-25 21:10:50 | 3.56427
(10 rows)

select   avg(process),
         date_trunc('hour',tstamp) as date
from     process
where    date_trunc('day', tstamp) = '2005-10-26'
group by date_trunc('hour', tstamp)
order by date_trunc('hour', tstamp);

       avg        |        date
------------------+---------------------
 9.79195118032606 | 2005-10-26 05:00:00
 10.0249767947376 | 2005-10-26 06:00:00
 8.88596018049452 | 2005-10-26 07:00:00
 7.95090951088542 | 2005-10-26 08:00:00
 8.10741349776586 | 2005-10-26 09:00:00
 7.30079822791947 | 2005-10-26 10:00:00
 7.10586501293712 | 2005-10-26 11:00:00
 8.15196838166979 | 2005-10-26 12:00:00
 8.26183129151662 | 2005-10-26 13:00:00
 8.95141531440947 | 2005-10-26 14:00:00
  10.562882253329 | 2005-10-26 15:00:00
 10.8634908244445 | 2005-10-26 16:00:00
 11.4077104069976 | 2005-10-26 17:00:00
 12.4702264580744 | 2005-10-26 18:00:00
 11.9155618293134 | 2005-10-26 19:00:00
 11.5622152555012 | 2005-10-26 20:00:00
 11.6527367563489 | 2005-10-26 21:00:00
 10.3170960432442 | 2005-10-26 22:00:00
 9.56747980806563 | 2005-10-26 23:00:00
(19 rows)