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2023-04-18
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import bounds from "./bounds";
import cut from "./cut";
import dedup from "./dedup";
import delta from "./delta";
import extract from "./extract";
import geometry from "./geometry";
import hashmap from "./hash/hashmap";
import prequantize from "./prequantize";
// Constructs the TopoJSON Topology for the specified hash of features.
// Each object in the specified hash must be a GeoJSON object,
// meaning FeatureCollection, a Feature or a geometry object.
export default function(objects, quantization) {
var bbox = bounds(objects = geometry(objects)),
transform = quantization > 0 && bbox && prequantize(objects, bbox, quantization),
topology = dedup(cut(extract(objects))),
coordinates = topology.coordinates,
indexByArc = hashmap(topology.arcs.length * 1.4, hashArc, equalArc);
objects = topology.objects; // for garbage collection
topology.bbox = bbox;
topology.arcs = topology.arcs.map(function(arc, i) {
indexByArc.set(arc, i);
return coordinates.slice(arc[0], arc[1] + 1);
});
delete topology.coordinates;
coordinates = null;
function indexGeometry(geometry) {
if (geometry && indexGeometryType.hasOwnProperty(geometry.type)) indexGeometryType[geometry.type](geometry);
}
var indexGeometryType = {
GeometryCollection: function(o) { o.geometries.forEach(indexGeometry); },
LineString: function(o) { o.arcs = indexArcs(o.arcs); },
MultiLineString: function(o) { o.arcs = o.arcs.map(indexArcs); },
Polygon: function(o) { o.arcs = o.arcs.map(indexArcs); },
MultiPolygon: function(o) { o.arcs = o.arcs.map(indexMultiArcs); }
};
function indexArcs(arc) {
var indexes = [];
do {
var index = indexByArc.get(arc);
indexes.push(arc[0] < arc[1] ? index : ~index);
} while (arc = arc.next);
return indexes;
}
function indexMultiArcs(arcs) {
return arcs.map(indexArcs);
}
for (var key in objects) {
indexGeometry(objects[key]);
}
if (transform) {
topology.transform = transform;
topology.arcs = delta(topology.arcs);
}
return topology;
}
function hashArc(arc) {
var i = arc[0], j = arc[1], t;
if (j < i) t = i, i = j, j = t;
return i + 31 * j;
}
function equalArc(arcA, arcB) {
var ia = arcA[0], ja = arcA[1],
ib = arcB[0], jb = arcB[1], t;
if (ja < ia) t = ia, ia = ja, ja = t;
if (jb < ib) t = ib, ib = jb, jb = t;
return ia === ib && ja === jb;
}