v0.2.2 updates the Visvalingam weighting function

Author: mbloch

mapshaper.js

@@ -3303,9 +3303,9 @@ MapShaper.getOptionParser = function() {
 
   // Work-in-progress (no .describe(), so hidden from -h)
   parser.command('tracing');
-  /*
   parser.command("flatten")
     .option("target", targetOpt);
+  /*
 
   parser.command("divide")
     .option("name", nameOpt)
@@ -5497,71 +5497,6 @@ Visvalingam.getArcCalculator = function(metric2D, metric3D, scale) {
 Visvalingam.standardMetric = triangleArea;
 Visvalingam.standardMetric3D = triangleArea3D;
 
-// Replacement for original "Modified Visvalingam"
-// Underweight polyline vertices with acute angles in proportion to 1 - cosine
-//
-Visvalingam.weightedMetric = function(ax, ay, bx, by, cx, cy) {
-  var area = triangleArea(ax, ay, bx, by, cx, cy);
-  return area * Visvalingam.weight(ax, ay, bx, by, cx, cy);
-};
-
-Visvalingam.weightedMetric3D = function(ax, ay, az, bx, by, bz, cx, cy, cz) {
-  var area = triangleArea3D(ax, ay, az, bx, by, bz, cx, cy, cz),
-      cos = cosine3D(ax, ay, az, bx, by, bz, cx, cy, cz),
-      weight = cos > 0 ? 1 - cos : 1;
-  return area * weight;
-};
-
-// deg.  weight
-// 180   1
-// 90    1
-// 60
-// 45
-// 0     0
-//
-Visvalingam.weightA = function(cos) {
-  return cos > 0 ? 1 - cos : 1;
-};
-
-// deg.  weight
-// 180   1
-// 90    1
-// 60
-// 45
-// 0     0
-//
-Visvalingam.weightB = function(cos) {
-  return cos > 0 ? 1 - cos * cos : 1;
-};
-
-Visvalingam.weightC = function(cos) {
-  return 0.5 - cos * 0.5;
-};
-
-// deg.  weight
-// 180   2
-// 90    1
-// 0     0
-//
-Visvalingam.weightD = function(cos) {
-  return 1 + -cos;
-};
-
-// deg.  weight
-// 180   1.5
-// 90    1
-// 0     0.5
-//
-Visvalingam.weightE = function(cos) {
-  return -cos * 0.5 + 1;
-};
-
-Visvalingam.weightF = function(cos) {
-  return -cos * 0.7 + 1;
-};
-
-Visvalingam.weight = Visvalingam.weightF;
-
 Visvalingam.weightedMetric = function(ax, ay, bx, by, cx, cy) {
   var area = triangleArea(ax, ay, bx, by, cx, cy),
       cos = cosine(ax, ay, bx, by, cx, cy);
@@ -5574,23 +5509,34 @@ Visvalingam.weightedMetric3D = function(ax, ay, az, bx, by, bz, cx, cy, cz) {
   return Visvalingam.weight(cos) * area;
 };
 
-// The original "modified Visvalingam" function used a step function to
+// Functions for weighting triangle area
+
+// The original Flash-based Mapshaper (ca. 2006) used a step function to
 // underweight more acute triangles.
-/*
-Visvalingam.weightedMetric_v1 = function(ax, ay, bx, by, cx, cy) {
-  var area = triangleArea(ax, ay, bx, by, cx, cy),
-      angle = innerAngle(ax, ay, bx, by, cx, cy),
-      weight = angle < 0.5 ? 0.1 : angle < 1 ? 0.3 : 1;
-  return area * weight;
+Visvalingam.weight_v1 = function(cos) {
+  var angle = Math.acos(cos),
+      weight = 1;
+  if (angle < 0.5) {
+    weight = 0.1;
+  } else if (angle < 1) {
+    weight = 0.3;
+  }
+  return weight;
 };
 
-Visvalingam.weightedMetric3D_v1 = function(ax, ay, az, bx, by, bz, cx, cy, cz) {
-  var area = triangleArea3D(ax, ay, az, bx, by, bz, cx, cy, cz),
-      angle = innerAngle3D(ax, ay, az, bx, by, bz, cx, cy, cz),
-      weight = angle < 0.5 ? 0.1 : angle < 1 ? 0.3 : 1;
-  return area * weight;
+// v2 weighting: underweight polyline vertices at acute angles in proportion to 1 - cosine
+Visvalingam.weight_v2 = function(cos) {
+  return cos > 0 ? 1 - cos : 1;
+};
+
+// v3 weighting: weight by inverse cosine
+// Standard weighting favors 90-deg angles; this curve peaks at 120 deg.
+Visvalingam.weight_v3 = function(cos) {
+  var k = 0.7;
+  return -cos * k + 1;
 };
-*/
+
+Visvalingam.weight = Visvalingam.weight_v3;
 
 
 
@@ -7988,7 +7934,6 @@ function PathImporter(reservedPoints, opts) {
   */
 
   // Import coordinates from an array with coordinates in format: [x, y, x, y, ...]
-  // (for Shapefile import -- consider moving out of here)
   //
   this.importPathFromFlatArray = function(arr, type) {
     var len = arr.length,
@@ -10429,7 +10374,6 @@ MapShaper.importShp = function(src, opts) {
   var importer = new PathImporter(pathPoints, opts);
 
   // TODO: test cases: null shape; non-null shape with no valid parts
-
   reader.forEachShape(function(shp) {
     importer.startShape();
     if (shp.isNull) return;
@@ -12754,16 +12698,37 @@ MapShaper.appendHolestoRings = function(cw, ccw) {
 
 
 
-// Remove overlapping polygon shapes
+// Flatten overlapping polygon shapes
 // (Unfinished)
-/*
-api.flattenLayer = function(lyr, arcs, opts) {
-  // MapShaper.divideArcs([lyr], arcs);
-  var shapes = MapShaper.flattenShapes(lyr.shapes, arcs);
-  var lyr2 = Utils.defaults({shapes: shapes, data: null}, lyr);
-  return lyr2;
+api.flattenLayer = function(lyr, dataset, opts) {
+  var nodes = MapShaper.divideArcs(dataset);
+  var flatten = MapShaper.getPolygonFlattener(nodes);
+  var lyr2 = {data: null};
+  lyr2.shapes = lyr.shapes.map(flatten);
+  // TODO: copy data over
+  return Utils.defaults(lyr2, lyr);
+};
+
+MapShaper.getPolygonFlattener = function(nodes) {
+  var flags = new Uint8Array(nodes.arcs.size());
+  var divide = MapShaper.getHoleDivider(nodes, flags);
+  var flatten = MapShaper.getRingIntersector(nodes, 'flatten', flags);
+
+  return function(shp) {
+    if (!shp) return null;
+    var cw = [],
+        ccw = [];
+
+    divide(shp, cw, ccw);
+    cw = flatten(cw);
+    ccw.forEach(MapShaper.reversePath);
+    ccw = flatten(ccw);
+    ccw.forEach(MapShaper.reversePath);
+
+    var shp2 = MapShaper.appendHolestoRings(cw, ccw);
+    return shp2 && shp2.length > 0 ? shp2 : null;
+  };
 };
-*/
 
 
 
@@ -13247,8 +13212,8 @@ api.runCommand = function(cmd, dataset, cb) {
   } else if (name == 'filter') {
     MapShaper.applyCommand(api.filterFeatures, targetLayers, arcs, opts.expression);
 
-  //} else if (name == 'flatten') {
-  //  newLayers = MapShaper.applyCommand(api.flattenLayer, targetLayers, arcs, opts);
+  } else if (name == 'flatten') {
+    newLayers = MapShaper.applyCommand(api.flattenLayer, targetLayers, dataset, opts);
 
   } else if (name == 'info') {
     api.printInfo(dataset);
@@ -13622,6 +13587,11 @@ Utils.extend(api.internal, {
 api.T = T;
 C.VERBOSE = false;
 
-module.exports = api;
+if (typeof define === "function" && define.amd) {
+  define("mapshaper", api);
+} else if (typeof module === "object" && module.exports) {
+  module.exports = api;
+}
+this.mapshaper = api;
 
 })();

package.json

@@ -1,6 +1,6 @@
 {
 	"name": "mapshaper",
-	"version": "0.2.1",
+	"version": "0.2.2",
 	"description": "A tool for editing vector datasets for mapping and GIS.",
 	"keywords": ["shapefile","topojson","geojson","cartography","simplification","topology","gis"],
 	"author": "Matthew Bloch <masiyou@gmail.com>",

test/visvalingam-test.js

@@ -69,4 +69,4 @@ describe("mapshaper-visvalingam.js", function() {
           v.weightedMetric(0, 0, 1, 8, 2, 0));
     })
   })
-})
+})

www/index.html

@@ -14,7 +14,7 @@
 
 <div id="page-wrapper">
 <div class="g-page-header">
-	<div class="g-mapshaper-logo">map<span class="g-logo-highlight">shaper</span> <span class="mshp-version">v. 0.2.0</span></div>
+	<div class="g-mapshaper-logo">map<span class="g-logo-highlight">shaper</span> <span class="mshp-version">v. 0.2.2</span></div>
 
 	<div id="g-simplify-control-wrapper"><div id="g-simplify-control"><span class="g-label">Simplify</span>
 		<div class="g-slider">