xg_area_center — 2D `xldgeom` op

• Data kinds: contour → feature

• Call: fullseye.apply(img, "xg_area_center", a=0.5, b=0.5) (the 2-D model is one image plus two scalar knobs a,b∈[0,1])

• HALCON equivalent: area_center_points_xld (the HALCON reference is a useful guide to its meaning and parameters)

xg_area_center: 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_area_center: stages (docs site)

Usage

Polygon area of the contour(s) via the shoelace formula (summed abs).

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

輪郭辞書 `{"shape": (H, W), "cs": [Nx2 の (row, col) 点列, ...]}` の各輪郭を

多角形とみなし、靴ひも公式 `0.5*|Σ(x_i*y_{i+1} - x_{i+1}*y_i)|` で面積を

求めて全輪郭の合計を返す。点が 3 個未満の輪郭は 0 として無視。`a, b` は

未使用。

返り値は `numpy.float64`(単位は画素²、正規化なし)。輪郭が無い・辞書で

ない・非有限値を含む輪郭は読み飛ばされ、合計に寄与しない(空なら 0.0)。

開いた輪郭でも「最後の点と最初の点を結んで閉じた多角形」の面積になる点に

注意(直線状の開輪郭では 0、折れ線の開輪郭でも非零になる)。絶対値を取る

ので点列の向き(時計回り/反時計回り)は結果に影響しない。自己交差する輪郭では

交差で符号が打ち消しあい、真の面積より小さく出る。名前に反して重心は

返さない(面積のみ)。同じ点集合の 2 次モーメントは `xg_moments`、bbox の

縦横比は `xg_height_width_ratio`。

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_area_center 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_eccentricity · xg_orientation · xg_elliptic_axis · 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_area_center — 2D xldgeom op