Squashing-factor render

The primary product: the line-of-sight integral of log₁₀ Q⊥ through the built volume. Q⊥ is the perpendicular squashing factor, the projection-robust variant of the classical Q; it is large exactly where neighbouring field lines are pulled apart, in the quasi-separatrix layers, and diverges at separatrices, so the integral renders the fine structure seen at a total solar eclipse.

qorona render data/coconut_corona.qor -o data/eclipse.png --fov 8 --longitude 317 --latitude 6.2

The flags that matter

• --fov: field of view (full width) in solar radii.
• --longitude, --latitude, --roll: sub-observer heliographic point and camera roll; or --observer earth|stereo-a|solo|psp to take a real observer's viewpoint at the timestamp (see Camera and viewpoint).
• --occult: the body treatment; see the occultation modes below.
• --preset: geometric depth weighting, large-fov or small-fov for the near-limb view (default large-fov).
• --step: line-of-sight sample spacing in solar radii (default 0.02).
• --width, --height: image size in pixels (default 1024).
• --export fits: also write the quantitative render (LOS-averaged log₁₀ Q⊥, float32, WCS-registered) beside the PNG; needs a timestamp. See Export to JHelioviewer.

qorona render --help shows the common options, --help-all the complete reference (display clamp, stretch percentiles, stamp placement, and more).

Near-limb view

Closing in on the low corona is a setting, not a different product: a small field of view with the matching depth weighting, --fov 3 --preset small-fov. This sun view uses the opaque body (--occult opaque) so the disk shows its surface Q⊥ structure rather than a dark eclipse disk.

qorona render data/coconut_corona.qor -o data/near-limb.png \
    --fov 3 --longitude 317 --latitude 6.2 --preset small-fov --step 0.002 --occult opaque

Small fields of view need a fine step

The default --step 0.02 is matched to whole-corona views. Close in, thin sheets alias at that spacing: drop to --step 0.002.

Occultation modes

--occult picks the treatment of the solar body: opaque (the solid 3-D body, shown in the near-limb view above), eclipse (the dark disk, the default), none (no body at all; the integral runs through the whole volume), and composite (below). At the whole-corona scale the disk is small and the modes look alike, so eclipse and none are compared here at the same near-limb setting as the opaque view above:

eclipse (default)	none

qorona render data/coconut_corona.qor -o data/occult-<mode>.png \
    --fov 3 --longitude 317 --latitude 6.2 --preset small-fov --step 0.002 --occult <mode>

composite is made for the whole-corona view: the eclipse image with the disk filled by the near-limb view, toned down so the corona stays dominant; --disk-tone and --disk-desat tune it.

qorona render data/coconut_corona.qor -o data/composite.png \
    --fov 8 --longitude 317 --latitude 6.2 --occult composite