d3-polygon module overview
d3-polygon provides geometric operations for two-dimensional polygons, including functions to compute area, centroid, convex hull, perimeter length, and test point containment.
d3-polygon
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d3-polygon operations
Polygon operations: d3.polygonArea (compute area), d3.polygonCentroid (compute centroid), d3.polygonHull (compute convex hull), d3.polygonContains (test point inside polygon), d3.polygonLength (compute perimeter length).
polygonArea signature and behavior
polygonArea(polygon) returns the signed area of a polygon represented as an array of [x, y] coordinate pairs. If vertices are in counterclockwise order (assuming origin at top-left), the returned area is positive; otherwise negative or zero. Example: d3.polygonArea([[1, 1], [1.5, 0], [2, 1]]) returns -0.5.
polygonCentroid signature and behavior
polygonCentroid(polygon) returns the centroid of a polygon represented as an array of [x, y] coordinate pairs. The centroid is returned as a [x, y] coordinate. Example: d3.polygonCentroid([[1, 1], [1.5, 0], [2, 1]]) returns [1.5, 0.6666666666666666].
polygonHull signature and algorithm
polygonHull(points) returns the convex hull of the specified points using Andrew's monotone chain algorithm. The returned hull is an array containing a subset of input points arranged in counterclockwise order. Returns null if points has fewer than three elements.
polygonContains signature and behavior
polygonContains(polygon, point) returns true if and only if the specified point (as [x, y] coordinates) is inside the specified polygon. Example: d3.polygonContains([[1, 1], [1.5, 0], [2, 1]], [1.5, 0.667]) returns true.
polygonLength signature and behavior
polygonLength(polygon) returns the length of the perimeter of the specified polygon represented as an array of [x, y] coordinate pairs. Example: d3.polygonLength([[1, 1], [1.5, 0], [2, 1]]) returns 3.23606797749979.
Polygon representation format
Polygons in d3-polygon are represented as arrays of two-element arrays [[x0, y0], [x1, y1], …]. Polygons may be closed (first and last points are the same) or open (they are different). Typically polygons are in counterclockwise order, assuming a coordinate system where the origin is in the top-left corner.