FA-70747 / GIS polygon topology / Member archive

Node degree classification in an arc-node topology: loop end count · case 02

Island rings closed by a single loop arc report their node as a dangle.

Member previewVariant 2 · 3 implementations · 8 checks per implementation

Case contract

Input [nodes, arcs] with integer node ids and arcs [arc_id, from, to]. Degree counts arc ends, so a loop adds 2 to its node. Label degree 0 "isolated", 1 "dangle", 2 "pseudo", 3 or more "node". Return [[node, degree, label], ...] in ascending numeric node order, including isolated nodes.

Why this case matters

Topology QA flags dangles (undershoots) and pseudo-nodes (unnecessary splits); miscounting loops turns valid island rings into errors.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
regression #3	`[[7, 2, "pseudo"], [8, 1, "dangle"]]`	`[[7, 3, "node"], [8, 1, "dangle"]]`	Failed

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