xg_gen_polygons — 2D `xldgeom` op

• Data kinds: contour → contour

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

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

xg_gen_polygons: 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.*

Sweeping knob a (0.1 / 0.5 / 0.9, the other knob at its default):

▸ xg_gen_polygons: knob a sweep (docs site)

*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_gen_polygons: stages (docs site)

On other images (synthetic scene / photo / coins. Top row: inputs, bottom row: their outputs. Knobs at default):

▸ xg_gen_polygons: other inputs (docs site)

Usage

Douglas-Peucker polyline simplification; eps = a * contour bbox diagonal.

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

各輪郭を Ramer-Douglas-Peucker 法で間引いて頂点数の少ない折れ線(多角形)に

する。始点と終点は必ず残し、区間の弦から最も離れた点の距離が `eps` を

超えればその点を採用して再帰的に分割する。`eps` は輪郭ごとに、その輪郭の

bbox の対角長 `hypot(Δrow, Δcol) に a`([0,1] に clip)を掛けた値。

`a=0 で eps=0(弦上に完全に乗る点だけ落ちる)、a` を上げるほど粗く

なり、`a=1 では両端の 2 点だけになる。b` は未使用。

返り値は `{"shape", "cs"}` の輪郭辞書。点が 3 個未満の輪郭はコピーのまま。

閉輪郭(先頭=末尾)は始点と終点が同じ点なので、`a` が大きいと 2 点(同一点)に

退化し、面積や向きの特徴量が 0 になる。閉輪郭の形を保ちたい場合は `a` を

小さめにする(実測では半径 5〜8 の楕円 101 点が `a=0.05` で 9 点)。

間引きは元の点の部分集合を返し、新しい点は作らない。後段の `xg_area_center`

や `xg_regress_contours` の計算量を減らす前処理、折れ線の角(頂点)検出に。

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_gen_polygons 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 `contour` as input)

identity · select_contours · smooth_contours · fit_line_contours · contours_to_region · count_contours · total_length · select_contours_xld

Same category (`xldgeom`)

xg_moments · xg_area_center · xg_eccentricity · xg_orientation · xg_elliptic_axis · xg_height_width_ratio · xg_regress_contours · xg_clip_contours

*Provenance: ops.py — 2D operator registry. This per-op note is generated by tools/opdocs.py md (do not hand-edit).*

xg_gen_polygons — 2D xldgeom op