PhoSim v3.6 creates too many snaps on large InstanceCatalog

[Scott Daniel]

When I run

./phosim grid_catalog.txt -p 2 -t 8 -o output/

using the attached Instance Catalog on a machine with 48 cores, PhoSim produces too many snaps. It produced 78 lsst_e files for R00_S12 before I manually stopped it.

Curiously, if I run ./phosim on grid_catalog_small.txt, I do not get that error.

I was using PhoSim version 3.6

[John Peterson]

i believe this is because we now have made the default to have all sensors turned on: the science sensors, the guiders, and the wavefront sensors. (note: we debated internally about this a lot, because others using the wavefront sensors & guiders were getting confused about why phosim kept refusing to output them).

if you happen to have a source on a guider it will produce a lot of frames for all the exposures, which is what i think your large catalog is doing. (r00_s12 is a guider).

if you add "camconfig 1" into your catalog it will ignore the wavefront sensors and the guiders. let us know if that works.

[Scott Daniel]

Adding 'camconfig 1' worked. Thanks.

Just curious: why do the guide chips generate so many snaps? It might be helpful to have a document somewhere indicating how the different classes of chips are simulated, so that users aren't startled the way I was.

[John Peterson]

its because a guider will readout many frames to watch the motion of guide stars during the exposure. In this case, you'll get an exposure every 0.1 second, meaning there will be 300+ in a typical visit.