Process CCD Obs.

Choose a measurement route

Requirements before measurement

• The comet is present in KOPR's local comet-element database.
• The active location, telescope and camera describe the observation.
• The comet-aligned image contains a usable two-dimensional FITS image and a celestial WCS when catalogue stars are required.
• The selected camera and binning are compatible with the image geometry.
• A manual aperture and its complete local background annulus fit inside valid image coverage.

The Stars image is optional. When available it is the preferred comparison-star surface and improves paired comet-candidate diagnostics. Without it, supported helpers may work in restricted Comet-only mode.

Scientific, Compact and external FITS input

WCCD measures physical pixel values, not raw on-disk integer codes. Astropy applies BSCALE, BZERO and BLANK; KOPR then copies the selected science image to a common C-contiguous float32 array.

• signed int16;
• pseudo-unsigned uint16 through FITS scaling;
• other scaled integer FITS;
• float32 and float64;
• science images in the primary or a supported image extension.

Coverage, clipping, saturation, PROVENANCE and COMETTRK extensions are skipped when locating the science image.

Ordinary external FITS can be measured manually when their image, WCS and required observation metadata are usable. WStack provenance improves pairing, saturation and helper diagnostics, but integer storage alone does not establish those contracts.

Open a manual observation

1. Click New observation. The dialog displays the active KOPR location, telescope and camera.
2. Enter the comet short name. Examples are 103P or C/2012 X1. KOPR refuses the observation if local orbital elements are unavailable.
3. Select Comet stack. This file is required. Click the empty or populated path field, press Enter/Return, or use Browse… to open the same file chooser. A WStack product marked with a non-comet STACKTYP is rejected.
4. Select Stars stack when available. It is optional for manual work, but strongly recommended because comparison stars are sharper in the star-aligned product. It uses the same interactive path field and Browse handler; the existing Clear button removes the optional path.
5. Confirm pair compatibility. KOPR checks that the two paths differ and compares filter, object identity, WStack pair links and the numerical EXPTIME represented by the Comet and Stars pixels. The accepted exposure values must agree within 0.001 s.

Observation date, time, filter, total integration and represented frame count are read from the comet stack. KOPR prefers midpoint metadata for a stack. During preflight it resolves the numerical EXPTIME represented by the stack pixels, validates it against the Stars stack when present, and freezes the accepted value for the observation. TOTEXP remains reporting metadata and is not substituted for the photometric scale. If required exposure metadata are absent, KOPR requests or rejects the value according to the supported input route. The current folder is remembered as the starting directory for the next file dialog.

Camera compatibility gate

KOPR evaluates camera compatibility before deciding whether a selection dialog is necessary. It reconstructs the native detector geometry from the FITS source dimensions and binning. An exact match is accepted silently as VERIFIED_EXACT. A unique configured camera whose active-area dimensions differ only by a supported border is accepted silently as VERIFIED_COMPATIBLE. The dialog opens only when the policy cannot identify one unambiguous verified camera; after an explicit selection, the chosen camera becomes the active KOPR camera.

Automatic helpers for a new observation

The New CCD/DSLR observation dialog can enable Automatic comet finder, Auto star measure and the dependent High-precision position — JPL Horizons (requires internet connection). Accepted checkbox values are stored as the next-dialog defaults through QSettings; Cancel does not save them. The actual helper run state remains local to the newly committed observation.

Finder and Auto Star Measure use compact progress dialogs. The interactive WCCD finder searches candidates within 120 arcsec of the expected position while retaining visual confirmation and Primary/Extended classification. The unattended complete automatic-photometry route remains limited to 30 arcsec.

Finder review labels automatic candidates consecutively C1..Cn; table rows and candidate circles are selectable. Clicking another visible object creates M1. R60 routes manual comet clicks, automatic candidates and M1 through the same bounded 2D Gaussian comet-centroid function. A valid cutout remains available even when no automatic candidate survives.

Auto Star Measure uses one pipeline for sparse and crowded fields. It accepts elongation up to 2.2 normally, 2.2–2.7 with a quality warning and rejects values above 2.7. R55 adds mask-aware centroiding, compact-profile FWHM measurement, a robust isolated-star PSF scale, a post-aperture blend check and balanced background fallback. If no plateau exists, the guarded aperture is 3.5 × robust FWHM; 3–7 final stars remain a warning and scatter above 0.15 mag remains a hard failure.

Auto Stars displays only the final validated catalogue markers and apertures in the main WCCD image, not intermediate processing stages. Its detailed selectable report remains open until closed.

Open the complete Automatic Helpers and Slice guide

Main WCCD controls

Measurement modes

The selector uses stable named identifiers: Measure Comet, Measure Tail, Measure Stars, Slice Through Comet, Slice Between Points and Fix Astrometry. Logic does not depend on their visual index.

Comparison-star catalogues

Catalogue markers require a celestial WCS. KOPR queries the selected magnitude family and transforms catalogue coordinates into image pixels. Without WCS, stars can still be entered manually through the search dialog, but the normal catalogue-assisted workflow is unavailable.

For an unfiltered C observation, KOPR selects a comparison band from the configured camera spectral peak where possible. The catalogue family follows the Preferred mag. catalog setting, but a manual APASS/Gaia choice remains in effect when the filter is changed.

Marker colours distinguish catalogue colour classes. A catalogue marker is only a candidate position; it becomes a measured reference star after aperture photometry succeeds. All objects used in one final solution must use the same magnitude source.

Unified Reference stars workflow

R77–R78 use one canonical, lossless reference-star model for both AutoStars and Manual Stars. Fields available from the richer source are retained instead of being discarded when stars move between automatic measurement, manual review and the final observation.

• Reference stars opens one scrollable dialog over the canonical collection, including larger star sets.
• Use is checked only when the star is effectively included in the current final ensemble. Pairwise-rejected stars, image-quality-rejected stars and stars disabled by the observer are displayed unchecked.
• Reason is the single visible explanation of exclusion. The former redundant Pairwise status column is not shown.
• A freshly edited or explicitly rechecked candidate remains selected while recalculation is pending. After Recalculate, the strict scientific policy is applied again and an incompatible star becomes unchecked.
• Internally, user_enabled still records the observer's explicit state and pairwise_accepted still records the derived solver result. The R80 hotfix changes only the table projection; it does not discard either state.
• Automatic and manual stars have canonical type parity and feed the same final solution.
• Process obs. and Af-rho consume the same accepted IDs; they do not create a second competing reference-star solution.

Internal pairwise audit details remain available for review and diagnostics but are not automatically copied into the ICQ free-text comment.

Manual measurement workflow

1. Set the aperture radius and verify saturation handling. Use a radius that includes the intended coma while leaving the complete background annulus inside valid image coverage. For a physical standard aperture, enter the radius in thousands of kilometres, for example 10kkm. Leave Saturation level untouched to use the automatic role-specific policy; edit it only when you intentionally need a direct numeric threshold for the active image.
2. Measure the comet on the Comet image. Choose Measure Comet and store the nuclear-condensation centre. Manual selection uses the same bounded 2D Gaussian comet-centroid model as finder candidates and M1. You can then use the existing image interaction or click Perform comet measure beside Aperture radius. The button becomes available only with a positive aperture and finite stored centre, switches to the Comet image when necessary and runs without a separate confirmation dialog. When the Comet image is already active, repeating the measurement preserves the current zoom and pan; a role change still performs the normal switch and redraw. The large coma aperture is never reused as the centroid search radius.
3. Inspect the drawn geometry. The green circle is the comet aperture. The two green squares bound the local square background annulus. A cropped annulus is rejected.
4. Measure comparison stars. Choose Measure Stars. KOPR switches to the star-aligned image when one is loaded. Click clean, isolated catalogue stars. Each measurement enters the same canonical reference-star collection used by AutoStars. Each accepted star is shown with a cyan circular aperture and square background annulus.
5. Reject unsuitable stars. Avoid saturation, no-data edges, blends, star trails, contaminated annuli and stars with obviously inconsistent photometry. Hold Shift and click near an already measured star to change the manual set, or review the lossless canonical collection and its separate user/solver states through Reference stars.
6. Optionally measure the tail. Choose Measure Tail and right-click the comet centre followed by the visible tail end. KOPR derives angular length and position angle from WCS.
7. Process the observation. Select an extinction season only when appropriate, add an optional comment and click Process obs..

The same manual aperture-radius field is used for comet and manually selected comparison-star measurements. Auto Star Measure can derive and commit one validated common stellar aperture for its accepted comparison stars.

Background, valid coverage and saturation

Same-image local background

Manual WCCD measures the sky in the same image as each object. The adopted level is the median of a complete square annulus linked to the aperture radius. Its inner square half-size is approximately 4/3 of the aperture radius and its outer half-size approximately 7/3. The object aperture itself is excluded.

The median is robust to sparse outliers, but it does not make a visibly contaminated annulus valid. Reject a measurement when the annulus contains a bright star/trail, strong gradient, residual coma or masked/no-data boundary.

Coverage checks

Only finite pixels with positive aperture weight are accepted. KOPR reports No data coverage when a circular aperture touches NaN pixels, typically along the reprojection edge. A complete background annulus must also fit; KOPR does not silently use a clipped asymmetric sample.

Automatic role-specific policy

Comet and Stars images retain independent saturation contracts. When a WStack product contains a complete, shape-compatible NSATVAL source-frame map, any aperture touching a marked pixel is rejected as saturated even when averaging or summation hides the clipped source value. The aggregate stack pixel is not compared with a per-source-frame ADC threshold in this mode.

Without a complete map, the shared resolver first obtains a base value in this order:

1. explicit detector or linearity metadata: SATURATE, SATLEVEL, MAXADU or ADC-MAX;
2. detector bit depth from ADCBITS, ADC-BITS, BITDEPTH, BITDEP or NBITS, converted to 2**bits - 1;
3. the physical storage ceiling for integer FITS from BITPIX, BSCALE and BZERO;
4. for floating FITS, 1.0 when finite data follow the common normalized 0–1 convention, otherwise an editable 65535 ADU fallback.

For an aggregate image whose pixel scale can exceed that base value, the common resolver converts the base limit into the current image domain using an integer multiplier. The effective limit must be at least the finite image maximum, but the maximum itself is never copied as the threshold. In the audited FLOAT32 SUM stack, base 65535, maximum 1036396.5625 and multiplier 16 produce an effective limit of 1048560 ADU.

Manual threshold override

Editing Saturation level activates a per-image manual base value. While it is active, KOPR intentionally ignores the complete source-frame map for that image. The same shared resolver converts the manual base into the effective image-domain threshold, so the same base produces the same effective limit whether it came from automatic FLOAT fallback or the WCCD field. The override survives redraw, remeasurement and Comet/Stars switching. Loading a new FITS resets only the replaced image slot. The tooltip and terminal log identify the active policy.

The same frozen role-specific policy is used by manual comparison-star photometry, ordinary comet apertures, PA-adaptive ACF and Auto Star Measure.

PA-adaptive ACF comet photometry

Manual WCCD uses the production pa-adaptive-upper-v1 algorithm. Each circular layer is modelled along position angle in a fixed 40° local window. Only positive outliers above the dynamic robust-noise threshold are limited; negative samples are not clipped.

The manual workflow freezes the bounded centroid, local background and calibration context before analysing the ring sequence. The user's chosen final aperture radius remains authoritative; Review Apply recalculates the ACF analysis inside the same frozen manual context.

Review comet ACF… is available below Reference stars after a successful ACF comet measurement. It belongs to the last successful ACF Comet result and can be opened while the Stars image or another measurement mode is active.

• Reset parameters returns to the original or last applied state.
• Apply to measurement validates the frozen identity and always commits the preview to the Comet slot.
• Close discards the preview.

The selected-ring PA graph follows the actual ACF state. With ACF ON, raw, upper-limit and filtered profiles are styled explicitly. With ACF OFF, clipping curves are not displayed because no ACF clipping is active.

The reported signal remains the cumulative PA-adaptive ACF value at the selected radius; a second ordinary aperture sum is not substituted afterward.

Open the complete ACF, centroid, Review and provenance guide.

Magnitude calculation and uncertainty

Exposure-normalized instrumental convention

Manual ordinary photometry, ACF measurements, curve-of-growth points and automatically transferred comparison stars use one convention:

m_inst = 40 - 2.5 log10(net_flux / EXPTIME)

net_flux is the weighted aperture signal after additive local-sky subtraction. EXPTIME is the numerical exposure represented by the stack pixels and is frozen during observation preflight. Local sky is not a photometric divisor. TOTEXP remains total-integration/reporting metadata and does not replace EXPTIME. KOPR does not introduce PHOTSCAL, KPRSCAL or a user-entered scale factor.

Canonical differential solution

AutoStars and manually measured stars are converted to one lossless canonical reference-star collection. Extinction is applied to each star quantity q_i before consistency selection. The strict global pairwise solver then selects a mutually consistent subset; it does not use a naive greedy remove-and-recompute sequence.

No two accepted stars may differ by 0.150 mag or more. A pair exactly on the 0.150-mag boundary therefore fails the strict policy. The user choice user_enabled is preserved separately from the derived pairwise_accepted state, so opening or rerunning the solution does not destroy the observer's selections.

The one canonical accepted-ID set and one common final solution are used by Process obs. and the Af-rho output. There is no parallel post-success scatter gate after the strict pairwise solution.

Results, curve of growth and saved files

After validation, the Observation output dialog contains:

• the fixed-width ICQ observation record;
• the CometObs text representation;
• filtered Afρ rows when a supported non-C passband is used;
• a graph of measured aperture magnitudes and the selected curve-of-growth model;
• buttons for COBS comparison, saving the figure, appending the ICQ record and closing the dialog.

Append ICQ code writes the record to <observer-code>.txt in the current KOPR working directory. Merely opening or closing the result dialog does not append it. Save figure writes a PNG chosen by the user.

Afρ and curve of growth

KOPR converts measured angular apertures to projected cometocentric radii and calculates Afρ for filtered observations within the configured maximum physical radius. Unfiltered C data do not produce a meaningful Afρ row because no solar passband magnitude is assigned.

The same physically interpretable curve-of-growth model is used in the plot and ICQ comment:

m(<rho) = m_ref + s log10(rho / rho_ref)
gamma = -2 - s / 2.5

The preferred reference radius is 10,000 km when it lies inside the measured interval; otherwise the geometric centre of that interval is used. KOPR may select a continuous broken power law only when at least four measured apertures lie on each side and the broken fit improves BIC by more than 6. Cumulative apertures are correlated, so a reported break is descriptive and must be checked against seeing, background residuals, trails and image boundaries.

ICQ free-text comment

The generated comment records the requested observation metadata, including the active location with coordinates, comet altitude, Moon altitude and the fitted CoG formula. A user-entered comment is appended after these generated fields. R58 does not append an automatic Saturation: sentence to Results, ICQ or COBS comments. Saturation validation and provenance remain active in the measurement diagnostics. Individual comparison-star magnitudes remain internal diagnostics and are not exported as a list.

Common problems

Measurement checklist

• Comet and Stars products belong to the same WStack group and use the same filter/exposure.
• Active location, telescope, camera and binning are correct.
• Observation midpoint and represented frame count are plausible.
• Comet centre is on the intended condensation, not a star or trail.
• Comet aperture captures the requested coma and remains inside valid coverage.
• Every local background annulus is complete and visually clean.
• Comparison stars are unsaturated, isolated and use one catalogue source.
• Manual and automatic CoG behaviour is physically plausible; no late negative drift or unbounded growth is ignored.
• The result dialog and optional Afρ/CoG graph have been reviewed before appending the ICQ record.
• The automatic JSON diagnostic is retained with the measured WStack products.

Related chapters

Prepare matched stacks · Configuration · FITS and output formats · Troubleshooting · Algorithm reference · Scientific / Compact output · ACF / Review guide · Automatic helpers / Slice