xg_elliptic_axis — 2D `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)

xg_elliptic_axis: input → output

*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)

Usage

Major/minor axis ratio sqrt(lambda_max/lambda_min) of the point set.

> The detailed description below is the original text — the summary and the headings are translated.

全輪郭の点(閉輪郭の重複終点は除く)の (row, col) 共分散行列の固有値から、

等価楕円の長軸/短軸比 `sqrt(λ_max/λ_min) を返す。a, b` は未使用。

返り値は `numpy.float64` で 1 以上。等方な点配置で 1、細長いほど大きい。

`λ_min <= 1e-12(全点が一直線)では λ_max > 1e-12` なら 1e6、そうで

なければ 1.0。それ以外でも上限 1e6 で打ち切る。点が 2 個未満なら 1.0。

非有限になった場合も 1.0 に落とす。[0,1] に正規化されていない量なので、

他の特徴量と並べる際はスケールに注意(1e6 の外れ値が出うる)。

`xg_eccentricity` は同じ固有値を [0,1] に写した版で、こちらは比を直接

見たいときに使う。軸ではなく外接矩形の縦横比なら `xg_height_width_ratio`

(こちらは向きに依存する)。

Detailed usage guide

• gallery2d_geometry family guide

References (sample data, literature)

• 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.

Try it in Studio

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

Runnable examples (verified samples that actually call this op)

• gallery2d_geometry — py -3.11 examples/gallery2d_geometry.py

Ops the type connects to (they accept `feature` as input)

identity · feature_to_img

Same category (`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).*

xg_elliptic_axis — 2D xldgeom op