Mosaicking

In order to coadd multiple visit images, you have to define the tract and determine wcs and flux scale.

Define tract

We use makeDiscreteSkyMap.py to define tract. Based on the coordinates in the header, the tract is determined as a square covering the entire observed area specified with –id. You have to select all visits and filters for each target (target field) because the tract definition depends on the selected data. In case of the object observed with two filters, if you execute makeDiscreteSkyMap.py to each filter data, the definition of tract/patch can be slightly different. It can cause failures of stack and multi-band analysis.

# Assume that a directory for reduction is ~/HSC, rerun name is test, and field name is test_field (you can check your field name with registry.sqlite3).
makeDiscreteSkyMap.py ~/HSC --calib ~/HSC/CALIB --rerun test --id field=test_field

# makeDiscreteSkyMap.py [data reduction directory] --calib [calib directory] --rerun [rerun name] --id [visit, field, filter..]
# Option
#       --id : Specify all data used to define tract.

You can see the following message when the process is finished successfully.

makeDiscreteSkyMap INFO: tract 0 has corners (177.676, 57.388), (173.867, 57.388), (173.752, 59.440), (177.790, 59.440) (RA, Dec deg) and 11 x 11 patches

# It means that the tract 0 which has 11x11 patch is determined

Mosaicking

Next, you need to match the wcs and flux scale of each visit/CCD data. It can be done by mosaic.py. This command generates a matched list of reference bright stars from each CCD in a given tract. Then it solves spatially-varying correction terms of relative positions and flux scales on different CCDs/visits.

# A directory for reduction is ~/HSC, and rerun name is test
# Execute to each filter
mosaic.py ~/HSC/ --calib ~/HSC/CALIB --rerun test --id visit=20878..20890:2 tract=0 ccd=0..103

# When you output mosaic validation in ~/HSC/rerun/mosaic_diag,
mosaic.py ~/HSC/ --calib ~/HSC/CALIB --rerun test --id visit=20878..20890:2 tract=0 ccd=0..103 --diagnostics --diagDir ~/HSC/rerun/mosaic_diag

# mosaic.py [data reduction directory] --calib [calib directory] --rerun [rerun name] --id [visit, field, filter, ccd] tract=[tract]
# Options
#       --id : Specify the object ID. You can also use field and filter. The tract must be selected here.
#       --diagnostics : Add this options if you want to output the results of validation.
#       --diagDir : Specify a output directory for validation.

Note

Depending on your machine environment, it takes over 30 minutes after the following messages;

Mosaic INFO: Reading catalogs…

Mosaic INFO: Use 1 cores for reading source catalog

After mosaicking is completed, you find flux scaling files fcr-[visit]-[ccd].fits and corrected wcs files wcs-[visit]-[ccd].fits in ~/HSC/rerun/[rerun]/jointcal-results/[tract].

If you add option –diagnostics, you also find the following validation result files in the directory specified by –diagDir.

  • Validation results in each visit

    • Positional offsets　　　　　　　　 : ResPosArrow2D_[visit].png
    • Residuals of flux to distortion pattern: fcont_[visit].png
    • Distortion pattern of reduceFlat　 : jcont_[visit].png（confirm that distributions is in a concentric fashion）

  • Validation results in all visit

    • Deviation from mean flux of each visit : DFlux2D.png
    • Residuals of fluxes　　　　　　　　　　 : ResFlux.png
    • Deviation in magnitudes of detected sources (※): MdM.png
    • Offsets of WCS　　　　　　　　　　 : PosDPos.png
    • Offsets of WCS　　　　　　　　　　 : ResPosScatter.png
  • Other outputs
    • catalog.fits
    • ccd.dat
    • ccdScale.dat
    • coeffs.dat
    • dmag.dat
    • dpos.dat

(※) MdM.png & ResPosScatter.png; Green points show deviation of catalogs in HSC pipeline from astrometry catalog while red points show deviation from the mean of all visit in sources which are not in MATCH catalog.

../_images/mosaic_diag_1.png
../_images/mosaic_diag_2.png
../_images/mosaic_diag_3.png

Applying the mosaic solution to each visit/CCD data

Then apply the wcs and flux scale determined by mosaic.py to each visit/CCD data.

Note

If you want to see each CCD and catalog precisely, do this step just after mosaic.py. Otherwise do this step at the end of all processing. If you do not need to calibrate wcs and zero-point, you don’t need this step.

Use calibrateExposure.py to apply the solution found with mosaic.py to CORR images.

# Applying the solution to the visit/CCD images
# Directory for reduction is ~/HSC, and rerun name is test
calibrateExposure.py ~/HSC --calib ~HSC/CALIB --rerun test --id field=NGC604 tract=0 ccd=0..103 -j 8

# calibrateExposure.py [data reduction directory] --calib [calib directory]  --rerun [rerun name] --id [field, tract, ccd] -j [the number of threads]
# Options
#       --id : In the example, the input data is selected as a combination of field, tract and ccd. You can also use the combination of visit and ccd.
#       -j : Specify the number of threads.

Then you find calibrated images named ~/HSC/rerun/[rerun]/[pointing]/[filter]/corr/[tract]/CALEXP-[visit]-[ccd].fits

Use calibrateCatalog.py to apply the mosaic.py’s solution to SRC catalogs.

# Applying the solution to catalogs.
# Directory for reduction is ~/HSC, and rerun name is test
calibrateCatalog.py ~/HSC --calib ~/HSC/CALIB --rerun test --id field=NGC604 tract=0 ccd=0..103 --config doApplyCalib=False -j 8

# calibrateCatalog.py [data reduction directory] --calib [calib directory] --rerun [rerun name] --id [field, tract, ccd] -j [the number of threads]
# Options
#       --id : Same as calibrateExposure.py, you can also use the combination of visit and ccd.
#       --config doApplyCalib=False : Add it if you do not calibrate fluxes to magnitudes.
#       -j : Specify the number of threads.

The calibrated catalogs are ~/HSC/rerun/[rerun]/[pointing]/[filter]/output/[tract]/CALSRC-[visit]-[ccd].fits.