cheap-ruler - npm Package Compare versions

Comparing version 2.1.0 to 2.2.0

cheap-ruler.js

@@ -19,7 +19,13 @@ (function(f){if(typeof exports==="object"&&typeof module!=="undefined"){module.exports=f()}else if(typeof define==="function"&&define.amd){define([],f)}else{var g;if(typeof window!=="undefined"){g=window}else if(typeof global!=="undefined"){g=global}else if(typeof self!=="undefined"){g=self}else{g=this}g.cheapRuler = f()}})(function(){var define,module,exports;return (function e(t,n,r){function s(o,u){if(!n[o]){if(!t[o]){var a=typeof require=="function"&&require;if(!u&&a)return a(o,!0);if(i)return i(o,!0);var f=new Error("Cannot find module '"+o+"'");throw f.code="MODULE_NOT_FOUND",f}var l=n[o]={exports:{}};t[o][0].call(l.exports,function(e){var n=t[o][1][e];return s(n?n:e)},l,l.exports,e,t,n,r)}return n[o].exports}var i=typeof require=="function"&&require;for(var o=0;o<r.length;o++)s(r[o]);return s})({1:[function(require,module,exports){
 
-    // units per degree on equator
-    this.d = (units === 'miles' ? 24901.55 : 40075.16) / 360;
+    var f = lat * Math.PI / 180;
 
-    // longitude correction based on latitude
-    this.e = Math.cos(lat * Math.PI / 180);
+    // multiplier for unit conversion
+    var m = units === 'miles' ?  1.609344 :
+            units === 'meters' ? 1000 : 1;
+
+    // longitude correction
+    this.kx = m * (111.41513 * Math.cos(f) - 0.09455 * Math.cos(3 * f) + 0.00012 * Math.cos(5 * f));
+
+    // latitude correction
+    this.ky = m * (111.13209 - 0.56605 * Math.cos(2 * f) + 0.0012 * Math.cos(4 * f));
 }
@@ -29,10 +35,10 @@
     distance: function (a, b) {
-        var dx = (a[0] - b[0]) * this.e;
-        var dy = a[1] - b[1];
-        return Math.sqrt(dx * dx + dy * dy) * this.d;
+        var dx = (a[0] - b[0]) * this.kx;
+        var dy = (a[1] - b[1]) * this.ky;
+        return Math.sqrt(dx * dx + dy * dy);
     },
 
     bearing: function (a, b) {
-        var dx = (b[0] - a[0]) * this.e;
-        var dy = b[1] - a[1];
+        var dx = (b[0] - a[0]) * this.kx;
+        var dy = (b[1] - a[1]) * this.ky;
         if (!dx && !dy) return 0;
@@ -46,6 +52,5 @@ var bearing = Math.atan2(-dy, dx) * 180 / Math.PI + 90;
         var a = (90 - bearing) * Math.PI / 180;
-        var d = dist / this.d;
         return [
-            p[0] + d * Math.cos(a) / this.e,
-            p[1] + d * Math.sin(a)
+            p[0] + Math.cos(a) * dist / this.kx,
+            p[1] + Math.sin(a) * dist / this.ky
         ];
@@ -73,3 +78,3 @@ },
 
-        return (Math.abs(sum) / 2) * this.e * this.d * this.d;
+        return (Math.abs(sum) / 2) * this.kx * this.ky;
     },
@@ -101,8 +106,8 @@
             var y = line[i][1];
-            var dx = (line[i + 1][0] - x) * this.e;
-            var dy = line[i + 1][1] - y;
+            var dx = (line[i + 1][0] - x) * this.kx;
+            var dy = (line[i + 1][1] - y) * this.ky;
 
             if (dx !== 0 || dy !== 0) {
 
-                var t = ((p[0] - x) * this.e * dx + (p[1] - y) * dy) / (dx * dx + dy * dy);
+                var t = ((p[0] - x) * this.kx * dx + (p[1] - y) * this.ky * dy) / (dx * dx + dy * dy);
 
@@ -114,9 +119,9 @@ if (t > 1) {
                 } else if (t > 0) {
-                    x += dx * t / this.e;
-                    y += dy * t;
+                    x += (dx / this.kx) * t;
+                    y += (dy / this.ky) * t;
                 }
             }
 
-            dx = (p[0] - x) * this.e;
-            dy = p[1] - y;
+            dx = (p[0] - x) * this.kx;
+            dy = (p[1] - y) * this.ky;
 
@@ -195,4 +200,4 @@ var sqDist = dx * dx + dy * dy;
     bufferPoint: function (p, buffer) {
-        var v = buffer / this.d;
-        var h = v / this.e;
+        var v = buffer / this.ky;
+        var h = buffer / this.kx;
         return [
@@ -207,4 +212,4 @@ p[0] - h,
     bufferBBox: function (bbox, buffer) {
-        var v = buffer / this.d;
-        var h = v / this.e;
+        var v = buffer / this.ky;
+        var h = buffer / this.kx;
         return [
@@ -211,0 +216,0 @@ bbox[0] - h,

debug.js

@@ -17,3 +17,3 @@ 'use strict';
 
-var distances = [1, 100, 1000, 5000];
+var distances = [1, 100, 500, 1000, 5000];
 
@@ -27,7 +27,8 @@ for (var i = 0; i < distances.length; i++) {
 
-        var p1 = ruler.destination([0, lat], dist / 2, 90);
-        var p2 = ruler.destination([0, lat], dist / 2, 90 - 180);
+        var p1 = ruler.destination([0, lat], dist / 2, 45);
+        var p2 = ruler.destination([0, lat], dist / 2, 45 - 180);
         var d = ruler.distance(p1, p2);
-        var d2 = turf.distance(turf.point(p1), turf.point(p2));
-        // var d2 = vincenty.distVincenty(p1[1], p1[0], p2[1], p2[0]).distance / 1000;
+        // var d = turf.distance(turf.point(p1), turf.point(p2));
+        // var d = fccDist(p1, p2, lat);
+        var d2 = vincenty.distVincenty(p1[1], p1[0], p2[1], p2[0]).distance / 1000;
         var err = Math.abs((d - d2) / d2);
@@ -42,1 +43,11 @@ var errStr = (Math.round(100 * 1e2 * err) / 1e2) + '%';
 }
+
+
+function fccDist(a, b, lat) {
+    var f = lat * Math.PI / 180;
+    var k1 = 111.13209 - 0.56605 * Math.cos(2 * f) + 0.0012 * Math.cos(4 * f);
+    var k2 = 111.41513 * Math.cos(f) - 0.09455 * Math.cos(3 * f) + 0.00012 * Math.cos(5 * f);
+    var dy = k1 * (a[1] - b[1]);
+    var dx = k2 * (a[0] - b[0]);
+    return Math.sqrt(dx * dx + dy * dy);
+}

index.js

@@ -18,7 +18,13 @@ 'use strict';
 
-    // units per degree on equator
-    this.d = (units === 'miles' ? 24901.55 : 40075.16) / 360;
+    var f = lat * Math.PI / 180;
 
-    // longitude correction based on latitude
-    this.e = Math.cos(lat * Math.PI / 180);
+    // multiplier for unit conversion
+    var m = units === 'miles' ?  1.609344 :
+            units === 'meters' ? 1000 : 1;
+
+    // longitude correction
+    this.kx = m * (111.41513 * Math.cos(f) - 0.09455 * Math.cos(3 * f) + 0.00012 * Math.cos(5 * f));
+
+    // latitude correction
+    this.ky = m * (111.13209 - 0.56605 * Math.cos(2 * f) + 0.0012 * Math.cos(4 * f));
 }
@@ -28,10 +34,10 @@
     distance: function (a, b) {
-        var dx = (a[0] - b[0]) * this.e;
-        var dy = a[1] - b[1];
-        return Math.sqrt(dx * dx + dy * dy) * this.d;
+        var dx = (a[0] - b[0]) * this.kx;
+        var dy = (a[1] - b[1]) * this.ky;
+        return Math.sqrt(dx * dx + dy * dy);
     },
 
     bearing: function (a, b) {
-        var dx = (b[0] - a[0]) * this.e;
-        var dy = b[1] - a[1];
+        var dx = (b[0] - a[0]) * this.kx;
+        var dy = (b[1] - a[1]) * this.ky;
         if (!dx && !dy) return 0;
@@ -45,6 +51,5 @@ var bearing = Math.atan2(-dy, dx) * 180 / Math.PI + 90;
         var a = (90 - bearing) * Math.PI / 180;
-        var d = dist / this.d;
         return [
-            p[0] + d * Math.cos(a) / this.e,
-            p[1] + d * Math.sin(a)
+            p[0] + Math.cos(a) * dist / this.kx,
+            p[1] + Math.sin(a) * dist / this.ky
         ];
@@ -72,3 +77,3 @@ },
 
-        return (Math.abs(sum) / 2) * this.e * this.d * this.d;
+        return (Math.abs(sum) / 2) * this.kx * this.ky;
     },
@@ -100,8 +105,8 @@
             var y = line[i][1];
-            var dx = (line[i + 1][0] - x) * this.e;
-            var dy = line[i + 1][1] - y;
+            var dx = (line[i + 1][0] - x) * this.kx;
+            var dy = (line[i + 1][1] - y) * this.ky;
 
             if (dx !== 0 || dy !== 0) {
 
-                var t = ((p[0] - x) * this.e * dx + (p[1] - y) * dy) / (dx * dx + dy * dy);
+                var t = ((p[0] - x) * this.kx * dx + (p[1] - y) * this.ky * dy) / (dx * dx + dy * dy);
 
@@ -113,9 +118,9 @@ if (t > 1) {
                 } else if (t > 0) {
-                    x += dx * t / this.e;
-                    y += dy * t;
+                    x += (dx / this.kx) * t;
+                    y += (dy / this.ky) * t;
                 }
             }
 
-            dx = (p[0] - x) * this.e;
-            dy = p[1] - y;
+            dx = (p[0] - x) * this.kx;
+            dy = (p[1] - y) * this.ky;
 
@@ -194,4 +199,4 @@ var sqDist = dx * dx + dy * dy;
     bufferPoint: function (p, buffer) {
-        var v = buffer / this.d;
-        var h = v / this.e;
+        var v = buffer / this.ky;
+        var h = buffer / this.kx;
         return [
@@ -206,4 +211,4 @@ p[0] - h,
     bufferBBox: function (bbox, buffer) {
-        var v = buffer / this.d;
-        var h = v / this.e;
+        var v = buffer / this.ky;
+        var h = buffer / this.kx;
         return [
@@ -210,0 +215,0 @@ bbox[0] - h,

package.json

 {
   "name": "cheap-ruler",
-  "version": "2.1.0",
+  "version": "2.2.0",
   "description": "A collection of fast approximations to common geographic measurements.",
@@ -5,0 +5,0 @@ "main": "index.js",

README.md

@@ -7,4 +7,7 @@ # cheap-ruler [![Build Status](https://travis-ci.org/mapbox/cheap-ruler.svg?branch=master)](https://travis-ci.org/mapbox/cheap-ruler)
 
-For distances under a hundred miles and not on the poles,
-the results are [typically within 0.1%](#precision) of corresponding Turf functions.
+The approximations are based on an [FCC-approved formula of ellipsoidal Earth projection](https://www.gpo.gov/fdsys/pkg/CFR-2005-title47-vol4/pdf/CFR-2005-title47-vol4-sec73-208.pdf).
+For distances under 500 kilometers and not on the poles,
+the results are very precise — within [0.1% margin of error](#precision)
+compared to [Vincenti formulas](https://en.wikipedia.org/wiki/Vincenty%27s_formulae),
+and usually much less for shorter distances.
 
@@ -172,18 +175,12 @@ ## Performance
 
-A table that shows the margin of error for `ruler.distance` compared to `turf.distance`:
+A table that shows the margin of error for `ruler.distance` compared to `node-vincenty`
+(a state of the art distance formula):
 
 | lat | 0° | 10° | 20° | 30° | 40° | 50° | 60° | 70° | 80° |
 | --- |  --- | --- | --- | --- | --- | --- | --- | --- | --- |
-| 1km | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% |
-| 100km | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.08% | 0.09% | 0.11% |
-| 1000km | 0.11% | 0.11% | 0.12% | 0.14% | 0.18% | 0.25% | 0.42% | 0.89% | 3.48% |
+| 1km | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% | 0% |
+| 100km | 0% | 0% | 0% | 0% | 0% | 0% | 0.01% | 0.01% | 0.04% |
+| 500km | 0% | 0% | 0% | 0.01% | 0.02% | 0.04% | 0.08% | 0.2% | 0.83% |
+| 1000km | 0% | 0% | 0.02% | 0.04% | 0.07% | 0.15% | 0.31% | 0.78% | 3.36% |
 
-The same table for a much more precise Vincenty distance formula (using `node-vincenty` module):
-
-| lat | 0° | 10° | 20° | 30° | 40° | 50° | 60° | 70° | 80° |
-| --- |  --- | --- | --- | --- | --- | --- | --- | --- | --- |
-| 1km | 0.34% | 0.32% | 0.26% | 0.17% | 0.06% | 0.06% | 0.17% | 0.26% | 0.31% |
-| 100km | 0.34% | 0.32% | 0.26% | 0.17% | 0.06% | 0.06% | 0.16% | 0.25% | 0.28% |
-| 1000km | 0.36% | 0.34% | 0.3% | 0.23% | 0.16% | 0.11% | 0.17% | 0.55% | 3.08% |
-
 Errors for all other methods are similar.

test/test.js

@@ -29,5 +29,5 @@ 'use strict';
         var actual = ruler.distance(points[i], points[i + 1]);
-        assertErr(t, expected, actual, 0.001, 'distance');
+        assertErr(t, expected, actual, 0.003, 'distance');
     }
-    t.pass('distance within 0.1%');
+    t.pass('distance within 0.3%');
     t.end();
@@ -40,5 +40,5 @@ });
         var actual = ruler.bearing(points[i], points[i + 1]);
-        assertErr(t, expected, actual, 0.0001, 'bearing');
+        assertErr(t, expected, actual, 0.005, 'bearing');
     }
-    t.pass('bearing within 0.01%');
+    t.pass('bearing within 0.05%');
     t.end();
@@ -52,6 +52,6 @@ });
         var actual = ruler.destination(points[i], 1.0, bearing);
-        assertErr(t, expected[0], actual[0], 3e-7, 'destination longitude');
-        assertErr(t, expected[1], actual[1], 3e-7, 'destination latitude');
+        assertErr(t, expected[0], actual[0], 1e-6, 'destination longitude');
+        assertErr(t, expected[1], actual[1], 1e-6, 'destination latitude');
     }
-    t.pass('destination within 3e-7');
+    t.pass('destination within 1e-6');
     t.end();
@@ -64,5 +64,5 @@ });
         var actual = ruler.lineDistance(lines[i]);
-        assertErr(t, expected, actual, 0.001, 'lineDistance');
+        assertErr(t, expected, actual, 0.003, 'lineDistance');
     }
-    t.pass('lineDistance within 0.1%');
+    t.pass('lineDistance within 0.3%');
     t.end();
@@ -77,5 +77,5 @@ });
         var actual = ruler.area([lines[i]]);
-        assertErr(t, expected, actual, 0.0002, 'area');
+        assertErr(t, expected, actual, 0.003, 'area');
     }
-    t.pass('area within 0.02%');
+    t.pass('area within 0.3%');
     t.end();
@@ -90,6 +90,6 @@ });
         var actual = ruler.along(lines[i], dist);
-        assertErr(t, expected[0], actual[0], 2e-7, 'along longitude');
-        assertErr(t, expected[1], actual[1], 2e-7, 'along latitude');
+        assertErr(t, expected[0], actual[0], 1e-6, 'along longitude');
+        assertErr(t, expected[1], actual[1], 1e-6, 'along latitude');
     }
-    t.pass('lineDistance within 0.1%');
+    t.pass('along point within 1e-6');
     t.end();
@@ -112,3 +112,3 @@ });
     var p = ruler.pointOnLine(line, [-77.034076, 38.882017]).point;
-    t.same(p, [-77.03051972665213, 38.88046894284234], 'pointOnLine');
+    t.same(p, [-77.03052697027461, 38.880457194811896], 'pointOnLine');
     t.end();
@@ -128,7 +128,8 @@ });
             turf.point(start), turf.point(stop), turf.linestring(line)).geometry.coordinates);
+
         var actual = ruler.lineDistance(ruler.lineSlice(start, stop, line));
 
-        assertErr(t, expected, actual, 0.001, 'lineSlice length');
+        assertErr(t, expected, actual, 0, 'lineSlice length');
     }
-    t.pass('lineSlice length within 0.1%');
+    t.pass('lineSlice length the same');
     t.end();
@@ -150,5 +151,5 @@ });
 
-        assertErr(t, expected, actual, 0.001, 'lineSliceAlong length');
+        assertErr(t, expected, actual, 1e-10, 'lineSliceAlong length');
     }
-    t.pass('lineSliceAlong length within 0.1%');
+    t.pass('lineSliceAlong length within 1e-10');
     t.end();
@@ -163,3 +164,3 @@ });
     var actual = ruler.lineDistance(ruler.lineSlice(start, stop, line));
-    t.equal(actual, 0.018665535420681036, 'lineSlice reversed length');
+    t.equal(actual, 0.018676802802910702, 'lineSlice reversed length');
     t.end();
@@ -170,10 +171,10 @@ });
     for (var i = 0; i < points.length; i++) {
-        var expected = turfPointBuffer(points[i], 0.01);
-        var actual = milesRuler.bufferPoint(points[i], 0.01);
-        assertErr(t, expected[0], actual[0], 1e-8, 'bufferPoint west');
-        assertErr(t, expected[1], actual[1], 1e-8, 'bufferPoint east');
-        assertErr(t, expected[2], actual[2], 1e-8, 'bufferPoint south');
-        assertErr(t, expected[3], actual[3], 1e-8, 'bufferPoint north');
+        var expected = turfPointBuffer(points[i], 0.1);
+        var actual = milesRuler.bufferPoint(points[i], 0.1);
+        assertErr(t, expected[0], actual[0], 3e-5, 'bufferPoint west');
+        assertErr(t, expected[1], actual[1], 3e-5, 'bufferPoint east');
+        assertErr(t, expected[2], actual[2], 3e-5, 'bufferPoint south');
+        assertErr(t, expected[3], actual[3], 3e-5, 'bufferPoint north');
     }
-    t.pass('point buffer error within 1e-8');
+    t.pass('point buffer error within 3e-5');
     t.end();
@@ -185,3 +186,3 @@ });
     var bbox2 = ruler.bufferBBox(bbox, 1);
-    t.same(bbox2, [29.989308794440007, 37.991016879283826, 40.01069120555999, 39.008983120716174], 'bufferBBox');
+    t.same(bbox2, [29.989319515875376, 37.99098271225711, 40.01068048412462, 39.00901728774289], 'bufferBBox');
     t.end();
@@ -188,0 +189,0 @@ });

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Improved metrics

Total package byte prevSize

45647

increased by1.77%

Lines of code

819

increased by1.87%

Worsened metrics

Number of lines in readme file

185

decreased by-1.6%

No dependency changes