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Camera and viewpoint

render, wl, fieldlines and run all use the same camera: a plane-of-sky view, the geometry of an eclipse photograph or a coronagraph image. The viewpoint is set in one of two ways: prescribe it, or fetch it from a real observer's position at the observation time.

Prescribing the viewpoint

  • --longitude, --latitude: where the camera sits, in degrees, as a heliographic longitude and latitude in the solution's frame. It always looks at Sun centre, so this pair is the sub-observer point.
  • --roll: rotation about the line of sight, in degrees counter-clockwise as the observer sees it. At the default 0 the image is solar-north-up.
  • --fov: the field of view, the full width of the image, in solar radii.
qorona render data/coconut_corona.qor -o data/eclipse.png --fov 8 --longitude 317 --latitude 6.2

The angles are read in the solution's own heliographic frame, exactly as given. Two frames are in use; they share the rotation axis, so latitudes agree, but not the zero meridian: in a Carrington frame (a run driven by a Carrington synoptic map) --longitude 317 is Carrington longitude 317; in a Stonyhurst frame (HEEQ; the input magnetogram rotated to the Earth-facing meridian) longitude 0 faces Earth at every time. To point at Earth by hand, print the two angles with sunpy, which comes with the default Qorona install:

from sunpy.coordinates import sun

t = "2025-10-09T18:19:52"  # an ISO-8601 UTC string, or a compact "20251009181952"
print(sun.L0(t).deg, sun.B0(t).deg)  # 316.29 6.24

L0 is the Carrington longitude of the point facing Earth and B0 its heliographic latitude: in a Carrington frame the pair goes straight into --longitude and --latitude; in a Stonyhurst frame the sub-Earth longitude is 0 by definition and only --latitude is needed.

Fetching the viewpoint from an observer

When the volume carries its observation time and frame (--timestamp and --frame at build, or the same flags on the render command), --observer resolves the viewpoint from the observer's ephemeris and expresses it in the solution's frame, so no angles are typed:

qorona render data/corona.qor -o data/eclipse.png --fov 8 --observer earth
qorona render data/corona.qor -o data/stereo.png --fov 8 --observer stereo-a
  • earth resolves offline (L0, B0).
  • stereo-a, solo (Solar Orbiter) and psp (Parker Solar Probe) query JPL Horizons, which needs network access; offline, the run stops with a message naming the manual fallback.

--observer sets the pointing itself, so --longitude and --latitude are refused alongside it. The observer's true distance also goes into the FITS export, and the same declared frame places the FITS observer and the SunJSON field lines in Carrington coordinates for JHelioviewer.

Declaring the frame

--frame carrington|stonyhurst (heeq is accepted for Stonyhurst) is declared at build and baked into the volume with the timestamp; render --frame and wl --frame declare it for a volume built without one, or override it. The run summary names the frame in use. Without a declaration Qorona falls back to Carrington, reports carrington frame (assumed), and prints one warning whenever a frame-dependent feature runs (--observer, --export fits, --export sunjson, or export-lines). If the frame of a solution is not known, prescribe the viewpoint by hand.