snapshot of https://github.com/blevesearch/bleve.git (master, 2026-09-15; blobs > 131072B omitted)

geo/sloppy.go

@@ -0,0 +1,59 @@
+//  Copyright (c) 2017 Couchbase, Inc.
+//
+// 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 geo
+
+import (
+	"math"
+)
+
+var earthDiameterPerLatitude []float64
+
+const (
+	radiusTabsSize = (1 << 10) + 1
+	radiusDelta    = (math.Pi / 2) / (radiusTabsSize - 1)
+	radiusIndexer  = 1 / radiusDelta
+)
+
+func init() {
+	// initializes the tables used for the sloppy math functions
+
+	// earth radius
+	a := 6378137.0
+	b := 6356752.31420
+	a2 := a * a
+	b2 := b * b
+	earthDiameterPerLatitude = make([]float64, radiusTabsSize)
+	earthDiameterPerLatitude[0] = 2.0 * a / 1000
+	earthDiameterPerLatitude[radiusTabsSize-1] = 2.0 * b / 1000
+	for i := 1; i < radiusTabsSize-1; i++ {
+		lat := math.Pi * float64(i) / (2*radiusTabsSize - 1)
+		one := math.Pow(a2*math.Cos(lat), 2)
+		two := math.Pow(b2*math.Sin(lat), 2)
+		three := math.Pow(float64(a)*math.Cos(lat), 2)
+		four := math.Pow(b*math.Sin(lat), 2)
+		radius := math.Sqrt((one + two) / (three + four))
+		earthDiameterPerLatitude[i] = 2 * radius / 1000
+	}
+}
+
+// earthDiameter returns an estimation of the earth's diameter at the specified
+// latitude in kilometers
+func earthDiameter(lat float64) float64 {
+	index := math.Mod(math.Abs(lat)*radiusIndexer+0.5, float64(len(earthDiameterPerLatitude)))
+	if math.IsNaN(index) {
+		return 0
+	}
+	return earthDiameterPerLatitude[int(index)]
+}