topojson simplify

server.js

@@ -76,42 +76,96 @@ async function handleRequest(req, resp) {
   }
 }
 
-async function processQueryRequest(req, resp) {
+// Allowed params (per topojson code)
+const NUMERIC_PARAMS = {
+  // 'planarArea': { 'desc': 'minimum planar triangle area (absolute)' },
+  // 'planarQuantile': { 'desc': 'minimum planar triangle area (quantile)', max: 1 },
+  'sphericalArea': {'desc': 'minimum spherical excess (absolute)'},
+  'sphericalQuantile': {'desc': 'minimum spherical excess (quantile)', max: 1},
+};
+
+function parseParams(req) {
+
   const sparql = req.query.sparql;
   if (!sparql) {
     throw new MyError(400, `bad sparql parameter`);
   }
 
   const type = req.params.type;
   if (type !== `geojson.json` && type !== `topojson.json`) {
-    throw new MyError(400, `bad type parameter`);
+    throw new MyError(400, `bad type parameter. Allows "geojson.json" and "topojson.json"`);
   }
 
-  const qres = await sparqlService.query(sparql, `id`);
+  let param, value;
+  for (const name of Object.keys(NUMERIC_PARAMS)) {
+    if (req.query.hasOwnProperty(name)) {
+      if (param) {
+        throw new Error(`${name} parameter cannot be used together with ${param}`);
+      }
+      value = parseFloat(req.query[name]);
+      const info = NUMERIC_PARAMS[name];
+      param = name;
+      if (!(value.toString() === req.query[name] && value >= 0 && value <= (info.max || Number.MAX_VALUE))) {
+        throw new Error(`${name} parameter, ${info.desc}, must be a non-negative number` +
+          (info.max ? ` not larger than ${info.max}` : ''));
+      }
+    }
+  }
 
-  const pres = await postgresService.query(secrets.table, Object.keys(qres));
+  const filter = req.params.filter;
+  if (filter !== undefined && filter !== `all` && filter !== `detached`) {
+    throw new MyError(400, `bad filter parameter. Allows "all" and "detached"`);
+  }
+
+  return {sparql, param, value, type, filter};
+}
+
+async function processQueryRequest(req, resp) {
+  let {sparql, param, value, type, filter} = parseParams(req);
 
+  const qres = await sparqlService.query(sparql, `id`);
+  const pres = await postgresService.query(secrets.table, Object.keys(qres));
   let result = PostgresService.toGeoJSON(pres, qres);
 
-  switch (type) {
-  case `geojson.json`:
-    resp.status(200).type(`application/geo+json`).send(result);
-    break;
+  console.log(new Date().toISOString(), type, param || 'noSimpl', value || 0, filter || 'noFilter', result.length, req.headers[`x-real-ip`], sparql);
 
-  case `topojson.json`:
+  if (param || type === `topojson.json`) {
 
     result = topojson.topology({data: JSON.parse(result)}, {
       // preserve all properties
-      "property-transform": feature => feature.properties
+      'property-transform': feature => feature.properties
     });
-    result = JSON.stringify(result);
 
-    resp.status(200).type(`application/topo+json`).send(result);
-    break;
+    if (param) {
+      const system = (param === 'sphericalArea' || param === 'sphericalQuantile') ? `spherical` : `planar`;
 
-  default:
-    throw new Error();
+      result = topojson.presimplify(result, topojson[system + `TriangleArea`]);
+
+      if (param === 'planarQuantile' || param === 'sphericalQuantile') {
+        value = topojson.quantile(result, value);
+        param = system + `Area`;
+        res.header(`X-Equivalent-${param}`, value.toString());
+      }
+
+      result = topojson.simplify(result, value);
+
+      if (filter) {
+        const filterFunc = filter === 'all' ? topojson.filterWeight : topojson.filterAttachedWeight;
+        result = topojson.filter(result, filterFunc(result, value, topojson[system + `RingArea`]));
+      }
+
+      const transform = result.transform;
+      if (transform) {
+        result = topojson.quantize(result, transform);
+      }
+
+      if (type === `geojson.json`) {
+        result = topojson.feature(result, result.objects.data);
+      }
+    }
   }
 
-  console.log(new Date().toISOString(), type, result.length, req.headers[`x-real-ip`], sparql);
+  const contentType = type === 'geojson.json' ? 'application/geo+json' : 'application/topo+json';
+
+  resp.status(200).type(contentType).send(result);
 }