Merge pull request #31 from pelias/line_centroid

linestring centroids

README.md

@@ -167,6 +167,8 @@ pbf2json.createReadStream( config )
 
 Make sure `Go` is installed and configured on your system, see: https://gist.github.com/missinglink/4212a81a7d9c125b68d9
 
+**Note:** You should install the latest version of Golang, at least `1.5+`, last tested on `1.6.2`
+
 ```bash
 sudo apt-get install mercurial;
 go get;
@@ -189,7 +191,7 @@ If you would like to compile a version of this lib for an architecture which isn
 
 ```bash
 go get;
-go build pbf2json.go;
+go build;
 chmod +x pbf2json;
 mv pbf2json build/pbf2json.{platform}-{arch};
 ```
@@ -205,4 +207,4 @@ $ node
 'x64'
 ```
 
-Then submit a pull request, you are awesome ;)
+Then submit a pull request, you are awesome ;)

compile.sh

@@ -2,67 +2,64 @@
 
 # note: you will need to follow the guide here to install the tools required
 # to cross-compile for different architectures on your host machine.
-# http://dave.cheney.net/2013/07/09/an-introduction-to-cross-compilation-with-go-1-1
-
-# change this path to match your env
-source /var/www/golang-crosscompile/crosscompile.bash
+# http://dave.cheney.net/2015/08/22/cross-compilation-with-go-1-5
 
 echo "[compile] linux arm";
-go-linux-arm build pbf2json.go;
+env GOOD=linux GOARCH=arm go build;
 chmod +x pbf2json;
 mv pbf2json build/pbf2json.linux-arm;
 
 # echo "[compile] linux i386";
-# go-linux-386 build pbf2json.go;
+# env GOOD=linux GOARCH=386 go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.linux-ia32;
 
 echo "[compile] linux x64";
-go-linux-amd64 build pbf2json.go;
+env GOOD=linux GOARCH=amd64 go build;
 chmod +x pbf2json;
 mv pbf2json build/pbf2json.linux-x64;
 
 # echo "[compile] darwin i386";
-# go-darwin-386 build pbf2json.go;
+# env GOOD=darwin GOARCH=386 go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.darwin-ia32;
 
 echo "[compile] darwin x64";
-go-darwin-amd64 build pbf2json.go;
+env GOOD=darwin GOARCH=amd64 go build;
 chmod +x pbf2json;
 mv pbf2json build/pbf2json.darwin-x64;
 
 # echo "[compile] windows i386";
-# go-windows-386 build pbf2json.go;
+# env GOOD=windows GOARCH=386 go build;
 # chmod +x pbf2json.exe;
 # mv pbf2json.exe build/pbf2json.win32-ia32;
 
 echo "[compile] windows x64";
-go-windows-amd64 build pbf2json.go;
+env GOOD=windows GOARCH=amd64 go build -o pbf2json.exe;
 chmod +x pbf2json.exe;
 mv pbf2json.exe build/pbf2json.win32-x64;
 
 # echo "[compile] freebsd arm";
-# go-freebsd-arm build pbf2json.go;
+# env GOOD=freebsd GOARCH=arm go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.freebsd-arm;
 
 # echo "[compile] freebsd i386";
-# go-freebsd-386 build pbf2json.go;
+# env GOOD=freebsd GOARCH=386 go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.freebsd-ia32;
 
 # echo "[compile] freebsd x64";
-# go-freebsd-amd64 build pbf2json.go;
+# env GOOD=freebsd GOARCH=amd64 go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.freebsd-x64;
 
 # echo "[compile] openbsd i386";
-# go-openbsd-386 build pbf2json.go;
+# env GOOD=openbsd GOARCH=386 go build;
 # chmod +x pbf2json;
 # mv pbf2json build/pbf2json.openbsd-ia32;
 
 # echo "[compile] openbsd x64";
-# go-openbsd-amd64 build pbf2json.go;
+# env GOOD=openbsd GOARCH=amd64 go build;
 # chmod +x pbf2json;
-# mv pbf2json build/pbf2json.openbsd-x64;
+# mv pbf2json build/pbf2json.openbsd-x64;

line_centroid.go

@@ -0,0 +1,29 @@
+package main
+
+import "github.com/paulmach/go.geo"
+
+// GetLineCentroid - compute the centroid of a line string
+func GetLineCentroid(ps *geo.PointSet) *geo.Point {
+
+	path := geo.NewPath()
+	path.PointSet = *ps
+
+	halfDistance := path.Distance() / 2
+	travelled := 0.0
+
+	for i := 0; i < len(path.PointSet)-1; i++ {
+
+		segment := geo.NewLine(&path.PointSet[i], &path.PointSet[i+1])
+		distance := segment.Distance()
+
+		// middle line segment
+		if (travelled + distance) > halfDistance {
+			var remainder = halfDistance - travelled
+			return segment.Interpolate(remainder / distance)
+		}
+
+		travelled += distance
+	}
+
+	return ps.GeoCentroid()
+}

line_centroid_test.go

@@ -0,0 +1,46 @@
+package main
+
+import (
+	"testing"
+
+	"github.com/paulmach/go.geo"
+	"github.com/stretchr/testify/assert"
+)
+
+// http://www.openstreetmap.org/way/46340228
+func TestGetLineCentroid(t *testing.T) {
+
+	var poly = geo.NewPointSet()
+	poly.Push(geo.NewPoint(-74.001559, 40.719743))
+	poly.Push(geo.NewPoint(-73.999914, 40.721679))
+	poly.Push(geo.NewPoint(-73.997783, 40.724195))
+	poly.Push(geo.NewPoint(-73.997318, 40.724745))
+	poly.Push(geo.NewPoint(-73.996797, 40.725375))
+	poly.Push(geo.NewPoint(-73.995203, 40.727239))
+	poly.Push(geo.NewPoint(-73.993927, 40.728737))
+	poly.Push(geo.NewPoint(-73.992407, 40.730535))
+	poly.Push(geo.NewPoint(-73.991545, 40.731566))
+	poly.Push(geo.NewPoint(-73.991417, 40.731843))
+	poly.Push(geo.NewPoint(-73.990745, 40.734738))
+	poly.Push(geo.NewPoint(-73.990199, 40.737495))
+	poly.Push(geo.NewPoint(-73.989630, 40.739735))
+	poly.Push(geo.NewPoint(-73.989370, 40.741459))
+	poly.Push(geo.NewPoint(-73.989219, 40.742233))
+	poly.Push(geo.NewPoint(-73.989119, 40.743025))
+	poly.Push(geo.NewPoint(-73.988699, 40.745262))
+	poly.Push(geo.NewPoint(-73.987904, 40.749446))
+	poly.Push(geo.NewPoint(-73.987417, 40.752149))
+	poly.Push(geo.NewPoint(-73.986938, 40.754016))
+	poly.Push(geo.NewPoint(-73.986833, 40.754345))
+	poly.Push(geo.NewPoint(-73.986321, 40.755897))
+	poly.Push(geo.NewPoint(-73.986117, 40.756513))
+	poly.Push(geo.NewPoint(-73.985720, 40.757348))
+	poly.Push(geo.NewPoint(-73.985433, 40.757980))
+	poly.Push(geo.NewPoint(-73.983607, 40.760503))
+	poly.Push(geo.NewPoint(-73.979957, 40.765504))
+	poly.Push(geo.NewPoint(-73.979264, 40.766480))
+
+	var centroid = GetLineCentroid(poly)
+	assert.Equal(t, 40.74239780132512, centroid.Lat())
+	assert.Equal(t, -73.98919819175188, centroid.Lng())
+}