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Diffstat (limited to 'vendor/github.com/golang/geo/s2/regioncoverer.go')
| -rw-r--r-- | vendor/github.com/golang/geo/s2/regioncoverer.go | 477 |
1 files changed, 0 insertions, 477 deletions
diff --git a/vendor/github.com/golang/geo/s2/regioncoverer.go b/vendor/github.com/golang/geo/s2/regioncoverer.go deleted file mode 100644 index 476e58559..000000000 --- a/vendor/github.com/golang/geo/s2/regioncoverer.go +++ /dev/null @@ -1,477 +0,0 @@ -// Copyright 2015 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 - -import ( - "container/heap" -) - -// RegionCoverer allows arbitrary regions to be approximated as unions of cells (CellUnion). -// This is useful for implementing various sorts of search and precomputation operations. -// -// Typical usage: -// -// rc := &s2.RegionCoverer{MaxLevel: 30, MaxCells: 5} -// r := s2.Region(CapFromCenterArea(center, area)) -// covering := rc.Covering(r) -// -// This yields a CellUnion of at most 5 cells that is guaranteed to cover the -// given region (a disc-shaped region on the sphere). -// -// For covering, only cells where (level - MinLevel) is a multiple of LevelMod will be used. -// This effectively allows the branching factor of the S2 CellID hierarchy to be increased. -// Currently the only parameter values allowed are 1, 2, or 3, corresponding to -// branching factors of 4, 16, and 64 respectively. -// -// Note the following: -// -// - MinLevel takes priority over MaxCells, i.e. cells below the given level will -// never be used even if this causes a large number of cells to be returned. -// -// - For any setting of MaxCells, up to 6 cells may be returned if that -// is the minimum number of cells required (e.g. if the region intersects -// all six face cells). Up to 3 cells may be returned even for very tiny -// convex regions if they happen to be located at the intersection of -// three cube faces. -// -// - For any setting of MaxCells, an arbitrary number of cells may be -// returned if MinLevel is too high for the region being approximated. -// -// - If MaxCells is less than 4, the area of the covering may be -// arbitrarily large compared to the area of the original region even if -// the region is convex (e.g. a Cap or Rect). -// -// The approximation algorithm is not optimal but does a pretty good job in -// practice. The output does not always use the maximum number of cells -// allowed, both because this would not always yield a better approximation, -// and because MaxCells is a limit on how much work is done exploring the -// possible covering as well as a limit on the final output size. -// -// Because it is an approximation algorithm, one should not rely on the -// stability of the output. In particular, the output of the covering algorithm -// may change across different versions of the library. -// -// One can also generate interior coverings, which are sets of cells which -// are entirely contained within a region. Interior coverings can be -// empty, even for non-empty regions, if there are no cells that satisfy -// the provided constraints and are contained by the region. Note that for -// performance reasons, it is wise to specify a MaxLevel when computing -// interior coverings - otherwise for regions with small or zero area, the -// algorithm may spend a lot of time subdividing cells all the way to leaf -// level to try to find contained cells. -type RegionCoverer struct { - MinLevel int // the minimum cell level to be used. - MaxLevel int // the maximum cell level to be used. - LevelMod int // the LevelMod to be used. - MaxCells int // the maximum desired number of cells in the approximation. -} - -type coverer struct { - minLevel int // the minimum cell level to be used. - maxLevel int // the maximum cell level to be used. - levelMod int // the LevelMod to be used. - maxCells int // the maximum desired number of cells in the approximation. - region Region - result CellUnion - pq priorityQueue - interiorCovering bool -} - -type candidate struct { - cell Cell - terminal bool // Cell should not be expanded further. - numChildren int // Number of children that intersect the region. - children []*candidate // Actual size may be 0, 4, 16, or 64 elements. - priority int // Priority of the candidate. -} - -type priorityQueue []*candidate - -func (pq priorityQueue) Len() int { - return len(pq) -} - -func (pq priorityQueue) Less(i, j int) bool { - // We want Pop to give us the highest, not lowest, priority so we use greater than here. - return pq[i].priority > pq[j].priority -} - -func (pq priorityQueue) Swap(i, j int) { - pq[i], pq[j] = pq[j], pq[i] -} - -func (pq *priorityQueue) Push(x interface{}) { - item := x.(*candidate) - *pq = append(*pq, item) -} - -func (pq *priorityQueue) Pop() interface{} { - item := (*pq)[len(*pq)-1] - *pq = (*pq)[:len(*pq)-1] - return item -} - -func (pq *priorityQueue) Reset() { - *pq = (*pq)[:0] -} - -// newCandidate returns a new candidate with no children if the cell intersects the given region. -// The candidate is marked as terminal if it should not be expanded further. -func (c *coverer) newCandidate(cell Cell) *candidate { - if !c.region.IntersectsCell(cell) { - return nil - } - cand := &candidate{cell: cell} - level := int(cell.level) - if level >= c.minLevel { - if c.interiorCovering { - if c.region.ContainsCell(cell) { - cand.terminal = true - } else if level+c.levelMod > c.maxLevel { - return nil - } - } else if level+c.levelMod > c.maxLevel || c.region.ContainsCell(cell) { - cand.terminal = true - } - } - return cand -} - -// expandChildren populates the children of the candidate by expanding the given number of -// levels from the given cell. Returns the number of children that were marked "terminal". -func (c *coverer) expandChildren(cand *candidate, cell Cell, numLevels int) int { - numLevels-- - var numTerminals int - last := cell.id.ChildEnd() - for ci := cell.id.ChildBegin(); ci != last; ci = ci.Next() { - childCell := CellFromCellID(ci) - if numLevels > 0 { - if c.region.IntersectsCell(childCell) { - numTerminals += c.expandChildren(cand, childCell, numLevels) - } - continue - } - if child := c.newCandidate(childCell); child != nil { - cand.children = append(cand.children, child) - cand.numChildren++ - if child.terminal { - numTerminals++ - } - } - } - return numTerminals -} - -// addCandidate adds the given candidate to the result if it is marked as "terminal", -// otherwise expands its children and inserts it into the priority queue. -// Passing an argument of nil does nothing. -func (c *coverer) addCandidate(cand *candidate) { - if cand == nil { - return - } - - if cand.terminal { - c.result = append(c.result, cand.cell.id) - return - } - - // Expand one level at a time until we hit minLevel to ensure that we don't skip over it. - numLevels := c.levelMod - level := int(cand.cell.level) - if level < c.minLevel { - numLevels = 1 - } - - numTerminals := c.expandChildren(cand, cand.cell, numLevels) - maxChildrenShift := uint(2 * c.levelMod) - if cand.numChildren == 0 { - return - } else if !c.interiorCovering && numTerminals == 1<<maxChildrenShift && level >= c.minLevel { - // Optimization: add the parent cell rather than all of its children. - // We can't do this for interior coverings, since the children just - // intersect the region, but may not be contained by it - we need to - // subdivide them further. - cand.terminal = true - c.addCandidate(cand) - } else { - // We negate the priority so that smaller absolute priorities are returned - // first. The heuristic is designed to refine the largest cells first, - // since those are where we have the largest potential gain. Among cells - // of the same size, we prefer the cells with the fewest children. - // Finally, among cells with equal numbers of children we prefer those - // with the smallest number of children that cannot be refined further. - cand.priority = -(((level<<maxChildrenShift)+cand.numChildren)<<maxChildrenShift + numTerminals) - heap.Push(&c.pq, cand) - } -} - -// adjustLevel returns the reduced "level" so that it satisfies levelMod. Levels smaller than minLevel -// are not affected (since cells at these levels are eventually expanded). -func (c *coverer) adjustLevel(level int) int { - if c.levelMod > 1 && level > c.minLevel { - level -= (level - c.minLevel) % c.levelMod - } - return level -} - -// adjustCellLevels ensures that all cells with level > minLevel also satisfy levelMod, -// by replacing them with an ancestor if necessary. Cell levels smaller -// than minLevel are not modified (see AdjustLevel). The output is -// then normalized to ensure that no redundant cells are present. -func (c *coverer) adjustCellLevels(cells *CellUnion) { - if c.levelMod == 1 { - return - } - - var out int - for _, ci := range *cells { - level := ci.Level() - newLevel := c.adjustLevel(level) - if newLevel != level { - ci = ci.Parent(newLevel) - } - if out > 0 && (*cells)[out-1].Contains(ci) { - continue - } - for out > 0 && ci.Contains((*cells)[out-1]) { - out-- - } - (*cells)[out] = ci - out++ - } - *cells = (*cells)[:out] -} - -// initialCandidates computes a set of initial candidates that cover the given region. -func (c *coverer) initialCandidates() { - // Optimization: start with a small (usually 4 cell) covering of the region's bounding cap. - temp := &RegionCoverer{MaxLevel: c.maxLevel, LevelMod: 1, MaxCells: minInt(4, c.maxCells)} - - cells := temp.FastCovering(c.region) - c.adjustCellLevels(&cells) - for _, ci := range cells { - c.addCandidate(c.newCandidate(CellFromCellID(ci))) - } -} - -// coveringInternal generates a covering and stores it in result. -// Strategy: Start with the 6 faces of the cube. Discard any -// that do not intersect the shape. Then repeatedly choose the -// largest cell that intersects the shape and subdivide it. -// -// result contains the cells that will be part of the output, while pq -// contains cells that we may still subdivide further. Cells that are -// entirely contained within the region are immediately added to the output, -// while cells that do not intersect the region are immediately discarded. -// Therefore pq only contains cells that partially intersect the region. -// Candidates are prioritized first according to cell size (larger cells -// first), then by the number of intersecting children they have (fewest -// children first), and then by the number of fully contained children -// (fewest children first). -func (c *coverer) coveringInternal(region Region) { - c.region = region - - c.initialCandidates() - for c.pq.Len() > 0 && (!c.interiorCovering || len(c.result) < c.maxCells) { - cand := heap.Pop(&c.pq).(*candidate) - - // For interior covering we keep subdividing no matter how many children - // candidate has. If we reach MaxCells before expanding all children, - // we will just use some of them. - // For exterior covering we cannot do this, because result has to cover the - // whole region, so all children have to be used. - // candidate.numChildren == 1 case takes care of the situation when we - // already have more than MaxCells in result (minLevel is too high). - // Subdividing of the candidate with one child does no harm in this case. - if c.interiorCovering || int(cand.cell.level) < c.minLevel || cand.numChildren == 1 || len(c.result)+c.pq.Len()+cand.numChildren <= c.maxCells { - for _, child := range cand.children { - if !c.interiorCovering || len(c.result) < c.maxCells { - c.addCandidate(child) - } - } - } else { - cand.terminal = true - c.addCandidate(cand) - } - } - c.pq.Reset() - c.region = nil -} - -// newCoverer returns an instance of coverer. -func (rc *RegionCoverer) newCoverer() *coverer { - return &coverer{ - minLevel: maxInt(0, minInt(maxLevel, rc.MinLevel)), - maxLevel: maxInt(0, minInt(maxLevel, rc.MaxLevel)), - levelMod: maxInt(1, minInt(3, rc.LevelMod)), - maxCells: rc.MaxCells, - } -} - -// Covering returns a CellUnion that covers the given region and satisfies the various restrictions. -func (rc *RegionCoverer) Covering(region Region) CellUnion { - covering := rc.CellUnion(region) - covering.Denormalize(maxInt(0, minInt(maxLevel, rc.MinLevel)), maxInt(1, minInt(3, rc.LevelMod))) - return covering -} - -// InteriorCovering returns a CellUnion that is contained within the given region and satisfies the various restrictions. -func (rc *RegionCoverer) InteriorCovering(region Region) CellUnion { - intCovering := rc.InteriorCellUnion(region) - intCovering.Denormalize(maxInt(0, minInt(maxLevel, rc.MinLevel)), maxInt(1, minInt(3, rc.LevelMod))) - return intCovering -} - -// CellUnion returns a normalized CellUnion that covers the given region and -// satisfies the restrictions except for minLevel and levelMod. These criteria -// cannot be satisfied using a cell union because cell unions are -// automatically normalized by replacing four child cells with their parent -// whenever possible. (Note that the list of cell ids passed to the CellUnion -// constructor does in fact satisfy all the given restrictions.) -func (rc *RegionCoverer) CellUnion(region Region) CellUnion { - c := rc.newCoverer() - c.coveringInternal(region) - cu := c.result - cu.Normalize() - return cu -} - -// InteriorCellUnion returns a normalized CellUnion that is contained within the given region and -// satisfies the restrictions except for minLevel and levelMod. These criteria -// cannot be satisfied using a cell union because cell unions are -// automatically normalized by replacing four child cells with their parent -// whenever possible. (Note that the list of cell ids passed to the CellUnion -// constructor does in fact satisfy all the given restrictions.) -func (rc *RegionCoverer) InteriorCellUnion(region Region) CellUnion { - c := rc.newCoverer() - c.interiorCovering = true - c.coveringInternal(region) - cu := c.result - cu.Normalize() - return cu -} - -// FastCovering returns a CellUnion that covers the given region similar to Covering, -// except that this method is much faster and the coverings are not as tight. -// All of the usual parameters are respected (MaxCells, MinLevel, MaxLevel, and LevelMod), -// except that the implementation makes no attempt to take advantage of large values of -// MaxCells. (A small number of cells will always be returned.) -// -// This function is useful as a starting point for algorithms that -// recursively subdivide cells. -func (rc *RegionCoverer) FastCovering(region Region) CellUnion { - c := rc.newCoverer() - cu := CellUnion(region.CellUnionBound()) - c.normalizeCovering(&cu) - return cu -} - -// normalizeCovering normalizes the "covering" so that it conforms to the current covering -// parameters (MaxCells, minLevel, maxLevel, and levelMod). -// This method makes no attempt to be optimal. In particular, if -// minLevel > 0 or levelMod > 1 then it may return more than the -// desired number of cells even when this isn't necessary. -// -// Note that when the covering parameters have their default values, almost -// all of the code in this function is skipped. -func (c *coverer) normalizeCovering(covering *CellUnion) { - // If any cells are too small, or don't satisfy levelMod, then replace them with ancestors. - if c.maxLevel < maxLevel || c.levelMod > 1 { - for i, ci := range *covering { - level := ci.Level() - newLevel := c.adjustLevel(minInt(level, c.maxLevel)) - if newLevel != level { - (*covering)[i] = ci.Parent(newLevel) - } - } - } - // Sort the cells and simplify them. - covering.Normalize() - - // If there are still too many cells, then repeatedly replace two adjacent - // cells in CellID order by their lowest common ancestor. - for len(*covering) > c.maxCells { - bestIndex := -1 - bestLevel := -1 - for i := 0; i+1 < len(*covering); i++ { - level, ok := (*covering)[i].CommonAncestorLevel((*covering)[i+1]) - if !ok { - continue - } - level = c.adjustLevel(level) - if level > bestLevel { - bestLevel = level - bestIndex = i - } - } - - if bestLevel < c.minLevel { - break - } - (*covering)[bestIndex] = (*covering)[bestIndex].Parent(bestLevel) - covering.Normalize() - } - // Make sure that the covering satisfies minLevel and levelMod, - // possibly at the expense of satisfying MaxCells. - if c.minLevel > 0 || c.levelMod > 1 { - covering.Denormalize(c.minLevel, c.levelMod) - } -} - -// SimpleRegionCovering returns a set of cells at the given level that cover -// the connected region and a starting point on the boundary or inside the -// region. The cells are returned in arbitrary order. -// -// Note that this method is not faster than the regular Covering -// method for most region types, such as Cap or Polygon, and in fact it -// can be much slower when the output consists of a large number of cells. -// Currently it can be faster at generating coverings of long narrow regions -// such as polylines, but this may change in the future. -func SimpleRegionCovering(region Region, start Point, level int) []CellID { - return FloodFillRegionCovering(region, cellIDFromPoint(start).Parent(level)) -} - -// FloodFillRegionCovering returns all edge-connected cells at the same level as -// the given CellID that intersect the given region, in arbitrary order. -func FloodFillRegionCovering(region Region, start CellID) []CellID { - var output []CellID - all := map[CellID]bool{ - start: true, - } - frontier := []CellID{start} - for len(frontier) > 0 { - id := frontier[len(frontier)-1] - frontier = frontier[:len(frontier)-1] - if !region.IntersectsCell(CellFromCellID(id)) { - continue - } - output = append(output, id) - for _, nbr := range id.EdgeNeighbors() { - if !all[nbr] { - all[nbr] = true - frontier = append(frontier, nbr) - } - } - } - - return output -} - -// TODO(roberts): The differences from the C++ version -// finish up FastCovering to match C++ -// IsCanonical -// CanonicalizeCovering -// containsAllChildren -// replaceCellsWithAncestor |