Add initial ‘geof’ package for geospatial functions

util/geof/geohash.go

@@ -0,0 +1,111 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package geof
+
+import (
+	"bytes"
+
+	"github.com/abcum/surreal/sql"
+)
+
+var bits = []int{16, 8, 4, 2, 1}
+
+var latmax = []float64{-90, 90}
+
+var lngmax = []float64{-180, 180}
+
+var base32 = []byte("0123456789bcdefghjkmnpqrstuvwxyz")
+
+func refine(interval []float64, cd, mask int) []float64 {
+	if cd&mask > 0 {
+		interval[0] = (interval[0] + interval[1]) / 2
+	} else {
+		interval[1] = (interval[0] + interval[1]) / 2
+	}
+	return interval
+}
+
+func GeohashDecode(hash string) *sql.Point {
+
+	isEven := true
+	lat := latmax
+	lng := lngmax
+	latErr := float64(90)
+	lngErr := float64(180)
+	var c string
+	var cd int
+
+	for i := 0; i < len(hash); i++ {
+		c = hash[i : i+1]
+		cd = bytes.Index(base32, []byte(c))
+		for j := 0; j < 5; j++ {
+			if isEven {
+				lngErr /= 2
+				lng = refine(lng, cd, bits[j])
+			} else {
+				latErr /= 2
+				lat = refine(lat, cd, bits[j])
+			}
+			isEven = !isEven
+		}
+	}
+
+	return sql.NewPoint(
+		(lat[0]+lat[1])/2,
+		(lng[0]+lng[1])/2,
+	)
+
+}
+
+func GeohashEncode(point *sql.Point, precision int64) string {
+
+	isEven := true
+	lat := []float64{-90, 90}
+	lng := []float64{-180, 180}
+	bit := 0
+	ch := 0
+	var geohash bytes.Buffer
+	var mid float64
+	for geohash.Len() < int(precision) {
+		if isEven {
+			mid = (lng[0] + lng[1]) / 2
+			if point.LO > mid {
+				ch |= bits[bit]
+				lng[0] = mid
+			} else {
+				lng[1] = mid
+			}
+		} else {
+			mid = (lat[0] + lat[1]) / 2
+			if point.LA > mid {
+				ch |= bits[bit]
+				lat[0] = mid
+			} else {
+				lat[1] = mid
+			}
+		}
+		isEven = !isEven
+		if bit < 4 {
+			bit++
+		} else {
+			geohash.WriteByte(base32[ch])
+			bit = 0
+			ch = 0
+		}
+	}
+
+	return geohash.String()
+
+}

util/geof/haversine.go

@@ -0,0 +1,34 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package geof
+
+import (
+	"math"
+
+	"github.com/abcum/surreal/sql"
+)
+
+const earthr float64 = 6371000
+
+const radian float64 = math.Pi / 180
+
+func Haversine(a, b *sql.Point) float64 {
+	lata, lnga := a.LA*radian, a.LO*radian
+	latb, lngb := b.LA*radian, b.LO*radian
+	latc, lngc := lata-latb, lnga-lngb
+	dis := math.Pow(math.Sin(latc/2), 2) + math.Cos(lata)*math.Cos(latb)*math.Pow(math.Sin(lngc/2), 2)
+	c := 2 * math.Atan2(math.Sqrt(dis), math.Sqrt(1-dis))
+	return earthr * c
+}

util/geof/inside.go

@@ -0,0 +1,19 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package geof
+
+func Inside(a, b interface{}) bool {
+	return false
+}

util/geof/intersects.go

@@ -0,0 +1,19 @@
+// Copyright © 2016 Abcum Ltd
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package geof
+
+func Intersects(a, b interface{}) bool {
+	return false
+}