HSM: measure PSF/star shapes directly in sky coords (use_sky_coords)#812
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cailmdaley wants to merge 5 commits into
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HSM: measure PSF/star shapes directly in sky coords (use_sky_coords)#812cailmdaley wants to merge 5 commits into
cailmdaley wants to merge 5 commits into
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Attach the local (Jacobian) WCS at each object position to the PSF/star stamps and pass use_sky_coords=True to galsim FindAdaptiveMom, so PSFEx and MCCD HSM ellipticities and sizes come out already in world coordinates. This makes the downstream WCS-Jacobian shape rotation (convert_psf_pix2world) redundant. Threaded at every in-repo HSM PSF/star call site: - psfex_interp: multi-epoch (per-CCD WCS log), single-exposure validation and classic (WCS from the galcat FITS_LDAC image header via _galcat_wcs) - mccd_interpolation_script: multi-epoch (per-CCD WCS log) - shapepipe_auxiliary_mccd: interpolation (WCS from galcat LDAC header) local_wcs_list() builds the per-object local WCS: use_sky_coords evaluates the stamp WCS at true_center, so it must be the full WCS linearised at the object's image position, not at the stamp centre. SIGMA_*_HSM (hence HSM_T_* = 2 sigma^2) is now in sky units (arcsec) rather than pixels; this is the intended, physically correct size. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w
HSM ellipticities and sizes are measured directly in world coordinates upstream, so the WCS-Jacobian shape rotation (transform_shape, getDecomposition) is redundant. Remove it from both the PSFEx and MCCD branches; the script keeps its remaining job of collating positions (X/Y/ RA/DEC), assigning the MCCD focal-plane CCD id, and merging per-exposure catalogues into per-patch star catalogues. Drops the galsim dependency. Caveat documented in the module docstring: the MCCD PSF_MOM_LIST/STAR_MOM_LIST columns come from the external mccd fit-validation code, still measured in the pixel frame; they are now passed through unrotated. Update the CANFAR doc to describe the step as collation, not pix->world shape conversion. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w
Equivalence test for use_sky_coords=True: draw an elliptical Gaussian on a stamp with a nontrivial local WCS (rotation + shear + 0.187 arcsec/pix scale, positive determinant), and assert that measuring in the pixel frame then applying the removed convert_psf_pix2world.transform_shape rotation (copied in verbatim as reference) agrees with measuring directly in sky coordinates, to numerical precision, for e1/e2 and sigma. A second test pins the deliberate unit change: the sky-frame sigma is the pixel sigma times the WCS scale. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w
…ranch The MCCD PSF_MOM_LIST/STAR_MOM_LIST columns come from the external mccd fit-validation code (mccd.auxiliary_fun.mccd_validation), which still measures HSM adaptive moments in the pixel frame. Stripping the WCS-Jacobian rotation there (71d502f) would have handed MergeStarCatMCCD pixel-frame ellipticities. Restore transform_shape + the per-CCD getDecomposition rotation for the MCCD MOM_LIST branch only (and the galsim import it needs); the in-repo PSFEx and MCCD-interpolation paths stay unrotated, as they now measure in world coordinates upstream. Update the module docstring caveat: this branch keeps the rotation until mccd itself adopts use_sky_coords. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w
local_wcs_list wraps galsim.AstropyWCS, which follows the 1-indexed FITS pixel convention, but the multi-epoch paths fed it positions from all_world2pix(..., 0) (origin 0) — evaluating the local Jacobian one pixel off. Compute a separate origin=1 position array (gal_pos_wcs) for local_wcs_list; the origin-0 gal_pos stays for the PSF-model interpolation (interpsfex / interp_MCCD), which is its only other use. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w
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We should revisit |
martinkilbinger
requested changes
Jul 14, 2026
| PSF/star ellipticities and sizes are now measured directly in sky coordinates | ||
| during PSF interpolation (galsim `FindAdaptiveMom(use_sky_coords=True)`), so | ||
| `convert_psf_pix2world.py` only collates and passes the shapes through. | ||
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Update to reflect removal of the patch concept in v2.0
cailmdaley
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Jul 16, 2026
Martin (PR #812 review): the patch concept is removed in v2.0. For -V v2.0 the handler reads summary/missing_job_32_all.txt and exp_numbers.txt relative to the run root instead of iterating P1..P9; -p restores an explicit P1..P<n> layout when needed. Co-Authored-By: Claude Fable 5 <noreply@anthropic.com> Claude-Session: https://claude.ai/code/session_01MqH9wjbJicVmaQdhZ4kBYr
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Closes #775.
ShapePipe measured PSF/star HSM adaptive moments in the pixel frame, then rotated the ellipticities into sky coordinates in a separate post-processing step (
scripts/python/convert_psf_pix2world.py, a WCS-Jacobian decomposition). galsim'sFindAdaptiveMomnow does this at the point of measurement viause_sky_coords=True(available since galsim 2.5; we pin ≥2.8) — per @aguinot's suggestion on #741. This PR moves the WCS knowledge into the HSM call and drops the redundant rotation.What changed
FindAdaptiveMomcall site — PSFEx single-exposure and multi-epoch (psfex_interp.py), MCCD interpolation (mccd_interpolation_script.py,shapepipe_auxiliary_mccd.py) — now attaches the local WCS (linearised at the object's image position) to the stamp and passesuse_sky_coords=True. Multi-epoch paths use the per-CCD WCS log already in scope; single-exposure paths read the WCS from the galcat'sLDAC_IMHEADheader.convert_psf_pix2world.pyno longer rotates the in-repoE1/E2/SIGMA_*_HSMshapes; it keeps its remaining jobs (position collation, MCCD CCD assignment, per-patch merge). CANFAR doc updated.PSF_MOM_LIST/STAR_MOM_LISTcolumns come from the externalmccdlibrary, which still measures in the pixel frame — that one branch keeps its rotation (with a docstring caveat) untilmccditself adoptsuse_sky_coords.tests/module/test_hsm_sky_coords.py: a synthetic Gaussian stamp under a nontrivial local WCS (0.187″/pix, 28° rotation, shear), measured pixel-frame + oldtransform_shapemath vsuse_sky_coords=True— g1/g2/sigma agree to rtol 1e-6. All 5 tests pass in the develop container.Notes for review
moments_sigmanow comes back in world units (arcsec) rather than pixels, soHSM_T_* = 2σ²is arcsec² — which is what the old pipeline produced after the rotation step, so end-of-pipeline catalogues are unchanged. Downstream consumers (merge_starcat, ngmix T-guess) checked: no pixel-scale assumption.getDecompositionto the HSM ellipticities;merge_starcatpasses them through.f153ea28).An independent adversarial review of the full diff ran before opening this PR; both findings it raised (the external-mccd branch above, and the indexing fix) are addressed.
— Claude on behalf of Cail
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https://claude.ai/code/session_01Gao7Pi5QDBgnTuagV7HT2w