# From opsim v4 to FBS 1.2

**URL:** <https://www.rubin.community/t/from-opsim-v4-to-fbs-1-2/3856>\
**Category:** Survey Strategy\
**Tags:** run-evaluation\
**Created:** [September 26, 2019, 7:00pm UTC](https://www.rubin.community/t/from-opsim-v4-to-fbs-1-2/3856 "2019-09-26T19:00:33Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![ljones](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/ljones/32/1804_2.png) [@ljones](https://www.rubin.community/u/ljones)\
**Post date:** [September 26, 2019, 7:00pm UTC](https://www.rubin.community/t/from-opsim-v4-to-fbs-1-2/3856/1 "2019-09-26T19:00:33Z")

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While it’s maybe not quite such a hot topic anymore, at some point there was a request for a comparison of opsim v4 (origin of ‘baseline2018a’) vs. the FBS. In part, this would be a description of the updated software - but I think perhaps the interesting part for a general audience would be also the effects of the difference.  
Building on some of the material Peter has presented in the past, I put this series of slides together for the AHM (but there was not time to present it then).

I was considering making this a technical note, but (a) it’s not clear this is required and (b) it has movies, which may not translate so well. In any case, I thought it might be worthwhile to circulate these slides to at least this audience.

Here are the slides - [[opsimV4ToFBS.pdf](https://www.rubin.community/uploads/short-url/3o5adjoIz0PqjQn8cNx0c2s5Xc7.pdf)] (1.9 MB PDF)  
and since the PDF can’t capture the movies (on slide 7), here are the two movies:  
the first shows the series of pointings in a single night within opsim v4 (baseline2018a) and the second is the series of pointings from the same night in a similar FBS 1.2 simulation (baseline\_2exp\_pairsame\_1\_2)

[https://www.rubin.community/uploads/short-url/3Dxd3Wb8vdA7iFiTOjdBkwbx5CS.mp4](https://www.rubin.community/uploads/short-url/3Dxd3Wb8vdA7iFiTOjdBkwbx5CS.mp4)

[https://www.rubin.community/uploads/short-url/2QcxXfpUjM2I0bIH8ghYl5JAswG.mp4](https://www.rubin.community/uploads/short-url/2QcxXfpUjM2I0bIH8ghYl5JAswG.mp4)

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**Author:** ![yoachim](https://sea2.discourse-cdn.com/flex002/user_avatar/www.rubin.community/yoachim/32/74_2.png) [@yoachim](https://www.rubin.community/u/yoachim)\
**Post date:** [September 26, 2019, 9:06pm UTC](https://www.rubin.community/t/from-opsim-v4-to-fbs-1-2/3856/2 "2019-09-26T21:06:02Z")

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Looks great! And you can see how at the end of the night the FBS reverts to a greedy algorithm and starts behaving like the old sims.