Initial QSfera import

Server/vendor/github.com/blevesearch/geo/s2/builder.go

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+// Copyright 2023 Google Inc. All rights reserved.
+//
+// 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 s2
+
+const (
+	// maxEdgeDeviationRatio is set so that MaxEdgeDeviation will be large enough
+	// compared to snapRadius such that edge splitting is rare.
+	//
+	// Using spherical trigonometry, if the endpoints of an edge of length L
+	// move by at most a distance R, the center of the edge moves by at most
+	// asin(sin(R) / cos(L / 2)). Thus the (MaxEdgeDeviation / SnapRadius)
+	// ratio increases with both the snap radius R and the edge length L.
+	//
+	// We arbitrarily limit the edge deviation to be at most 10% more than the
+	// snap radius. With the maximum allowed snap radius of 70 degrees, this
+	// means that edges up to 30.6 degrees long are never split. For smaller
+	// snap radii, edges up to 49 degrees long are never split. (Edges of any
+	// length are not split unless their endpoints move far enough so that the
+	// actual edge deviation exceeds the limit; in practice, splitting is rare
+	// even with long edges.) Note that it is always possible to split edges
+	// when MaxEdgeDeviation is exceeded.
+	maxEdgeDeviationRatio = 1.1
+)