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2023-04-18
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// Extracts the lines and rings from the specified hash of geometry objects.
//
// Returns an object with three properties:
//
// * coordinates - shared buffer of [x, y] coordinates
// * lines - lines extracted from the hash, of the form [start, end]
// * rings - rings extracted from the hash, of the form [start, end]
//
// For each ring or line, start and end represent inclusive indexes into the
// coordinates buffer. For rings (and closed lines), coordinates[start] equals
// coordinates[end].
//
// For each line or polygon geometry in the input hash, including nested
// geometries as in geometry collections, the `coordinates` array is replaced
// with an equivalent `arcs` array that, for each line (for line string
// geometries) or ring (for polygon geometries), points to one of the above
// lines or rings.
export default function(objects) {
var index = -1,
lines = [],
rings = [],
coordinates = [];
function extractGeometry(geometry) {
if (geometry && extractGeometryType.hasOwnProperty(geometry.type)) extractGeometryType[geometry.type](geometry);
}
var extractGeometryType = {
GeometryCollection: function(o) { o.geometries.forEach(extractGeometry); },
LineString: function(o) { o.arcs = extractLine(o.arcs); },
MultiLineString: function(o) { o.arcs = o.arcs.map(extractLine); },
Polygon: function(o) { o.arcs = o.arcs.map(extractRing); },
MultiPolygon: function(o) { o.arcs = o.arcs.map(extractMultiRing); }
};
function extractLine(line) {
for (var i = 0, n = line.length; i < n; ++i) coordinates[++index] = line[i];
var arc = {0: index - n + 1, 1: index};
lines.push(arc);
return arc;
}
function extractRing(ring) {
for (var i = 0, n = ring.length; i < n; ++i) coordinates[++index] = ring[i];
var arc = {0: index - n + 1, 1: index};
rings.push(arc);
return arc;
}
function extractMultiRing(rings) {
return rings.map(extractRing);
}
for (var key in objects) {
extractGeometry(objects[key]);
}
return {
type: "Topology",
coordinates: coordinates,
lines: lines,
rings: rings,
objects: objects
};
}