Screenshot 2024-01-19 at 5.14.22 AM.png
subimage.fits
[INSTRM-2150] Inconsistency of the second moments of MCS centroid measurement Created: 19/Jan/24 Updated: 24/Jan/24 |
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| Status: | Open |
| Project: | Instrument control development |
| Component/s: | ics_mcsActor |
| Affects Version/s: | None |
| Fix Version/s: | None |
| Type: | Task | Priority: | Normal |
| Reporter: | chyan | Assignee: | karr |
| Resolution: | Unresolved | Votes: | 0 |
| Labels: | None | ||
| Remaining Estimate: | Not Specified | ||
| Time Spent: | Not Specified | ||
| Original Estimate: | Not Specified | ||
| Attachments: |
Screenshot 2024-01-19 at 5.14.22 AM.png
subimage.fits
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| Description |
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During the MCS alignment, we used MPFIT for fitting 2D gaussian function to determine the spot sizes. We were expecting to use the second moments from database table `mcs_data`. However, the FWHMs calculated from second moments are not consistent with MPFIT of Python and IDL version. We should double check the consistency, so that we can use those information for MCS image quality check. |
| Comments |
| Comment by chyan [ 19/Jan/24 ] |
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Attached image is spot 1743 of frame 10504000. According to the data base entry, the second moments are 1.249642, 3.701665, which lead the FWHM = 2.63259298, 4.53095207. However, MPFIT of python and IDL version give sigma = 0.98, 1.26 (FWHM = 2.3079, 2.9673). These numbers are not consistent. |
| Comment by karr [ 23/Jan/24 ] |
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This is expected. The MCS code uses a windowed second moment, not an isophotal (like the default sextractor) or a fitted function (like MPFIT), and we don't expect them to be the same, although they will show similar relative behaviour. |