More UW eLSST OpSim Documentation

We have created an 'enhanced' version of the Opsim output to help with evaluating science cases. These enhancements are :

Dithering

The standard opsim currently uses fixed field centers (fixed RA/Dec) for all observations. These field centers remain the same over the entire simulation and each of these pointings has a unique ID (=fieldID).

We are currently looking at methods to dither observations and to evaluate the effects of those dithers (such as using pixelation maps). As a test case of dithering, we have added dithers to the field centers of our version of the OpSim database according to a pattern which results in dithers over the entire field of view:

This information is added into our opsim database in the columns hexdithra, hexdithdec, vertex. Thus if you would like to (for example) retrieve all observations of a particular RA/Dec, you can either query on fieldRA/fieldDec (for the fixed field centers) or hexdithra, hexdithdec (for the dithered field centers).

Very roughly speaking (we do use the proper trig to do this correctly in the tools) this corresponds to : 

mysql> select expmjd from output_opsim1_29 
where (fieldDec between -30.00*3.1415/180 and -27*3.1415/180) 
and (fieldRA between 30.0*3.1415/180 and 33.6*3.1415/180) 
order by expmjd limit 10;
+--------------+
| expmjd       |
+--------------+
| 49353.036182 | 
...
| 49357.037423 | 
| 49357.045958 | 
+--------------+
10 rows in set (0.05 sec)

mysql> select expmjd from output_opsim1_29 
where (hexdithdec between -30.00*3.1415/180 and -27*3.1415/180) 
and (hexdithra between 30.0*3.1415/180 and 33.6*3.1415/180) 
order by expmjd limit 10;
+--------------+
| expmjd       |
+--------------+
| 49353.036182 | 
...
| 49357.045958 | 
| 49357.046405 | 
+--------------+
10 rows in set (0.10 sec)

"Night" information

A column for "night" has been added to the opsim output to indicate which observing night an observation belongs to. The 'night' counter starts on night=0 at the start of the survey (usually), for uniformity between night counters on different simulations. The night is then indexed.
This was added primarily to aid with identifying observations suitable to matching to moving object ephemeris predictions. It is also be useful for identifying observations which were taken on the same night, as in the following : 

mysql> select (a.expmjd - b.expmjd)*24*60 as Time_Diff, a.expmjd, b.expmjd,  a.filter, b.filter 
from (select * from output_opsim1_29 where night=100 order by expmjd) as a,  
  (select * from output_opsim1_29 where night=100 order by expmjd) as b
where a.fieldid=b.fieldid and (a.expmjd>b.expmjd); 
+-----------------+--------------+--------------+--------+--------+
| Time_Diff       | expmjd       | expmjd       | filter | filter |
+-----------------+--------------+--------------+--------+--------+
| 19.883520004805 | 49452.986571 | 49452.972763 | z      | z      | 
| 19.883520004805 |  49452.98702 | 49452.973212 | z      | z      | 
.......   
| 19.353600003524 | 49453.419001 | 49453.405561 | z      | z      | 
| 18.712800006615 |  49453.41945 | 49453.406455 | z      | z      | 
+-----------------+--------------+--------------+--------+--------+
1881 rows in set (1.12 sec)
which can then be expanded using a simple python script (for example) to query all 3253 nights of the opsim.

For further questions or to request additional features, please contact Lynne Jones or Simon Krughoff.