xldgeom op• Data kinds: contour → feature
• Call: fullseye.apply(img, "xg_elliptic_axis", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])
• HALCON equivalent: elliptic_axis_points_xld (the HALCON reference is a useful guide to its meaning and parameters)
*The figure is the actual output on a synthetic 128×128 input. Left: input, right: output. Point clouds are drawn as a top-down scatter (brightness = z), 1-D series as a line plot, volumes as the maximum-intensity projection along z, videos as the middle frame, complex images as magnitude; return values that are not pictures are shown as the values themselves.*
*Knob a does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
*Knob b does not change the output (measured: identical at 0.1 / 0.5 / 0.9).*
Stages (the ops that come before → this op, left to right):
▸ xg_elliptic_axis: stages (docs site)
Major/minor axis ratio sqrt(lambda_max/lambda_min) of the point set.
From the eigenvalues of the (row, col) covariance matrix of all contour points (excluding the duplicated end point of closed contours), returns the major/minor axis ratio of the equivalent ellipse sqrt(λ_max/λ_min). a, b are unused.
Returns a numpy.float64 >= 1. 1 for isotropic point layouts, larger the more elongated. For λ_min <= 1e-12 (all points on one line): 1e6 if λ_max > 1e-12, otherwise 1.0. In other cases it is also capped at 1e6. 1.0 if there are fewer than 2 points. It also falls back to 1.0 if the value becomes non-finite. Since this quantity is not normalised to [0,1], mind the scale when placing it next to other features (outliers of 1e6 can occur). xg_eccentricity maps the same eigenvalues into [0,1]; use this one when you want to see the ratio directly. For the aspect ratio of the bounding rectangle rather than of the axes, use xg_height_width_ratio (which depends on orientation).
• gallery2d_geometry family guide
• Sample-data catalog (download URLs / licences) — 2-D uses skimage.data (BSD/public domain) plus synthetic images; 3-D lists download URLs for real data sources (Stanford, PDS, …).
• Operator provenance and references — the sources of the research/methods this op family came from.
• The canonical algorithm (author, year) and its uses are named in the family usage guide above.
The program below has been verified to run (same input as the figure). In Studio's help this block becomes buttons that load and run it on the spot.
threshold 0.50 0.50 sk_find_contours 0.50 0.50 xg_elliptic_axis 0.50 0.50
▸ Load this pipeline · Load & run
• gallery2d_geometry — py -3.11 examples/gallery2d_geometry.py
feature as input)xldgeom)xg_moments · xg_area_center · xg_eccentricity · xg_orientation · xg_height_width_ratio · xg_regress_contours · xg_clip_contours · xg_gen_polygons
*Provenance: ops.py — 2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*
© 2026 Kazufumi Furuse — Fullseye operator documentation. Licensed under Apache-2.0.