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I changed style slightly to better fit in with the rest of the project's code, added some missing comments where needed, and added in the commented code that the unchanged bounds must be copied to both of the new bboxes if it is later refactored to work that way.
This commit is contained in:
umpc 2016-10-13 06:17:45 -04:00 committed by GitHub
parent c665c324ff
commit 05de7283b4
1 changed files with 19 additions and 15 deletions
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34
geojson/bbox.go
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@ -187,49 +187,47 @@ func BBoxesFromCenter(lat, lon, meters float64) (outer BBox) {
return outer return outer
} }
func BBoxBounds(lat, lon, meters float64) (float64, float64, float64, float64) { func BBoxBounds(lat, lon, meters float64) (latMin, lonMin, latMax, lonMax float64) {
// see http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#Latitude // see http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#Latitude
lat = toRadians(lat)
lon = toRadians(lon)
r := meters / earthRadius // angular radius r := meters / earthRadius // angular radius
φ1 := toRadians(lat) latMin = lat - r
λ1 := toRadians(lon) latMax = lat + r
latMin := φ1 - r latT := math.Asin(math.Sin(lat) / math.Cos(r))
latMax := φ1 + r lonΔ := math.Acos(( math.Cos(r) - math.Sin(latT) * math.Sin(lat)) / (math.Cos(latT) * math.Cos(lat) ))
latT := math.Asin(math.Sin(φ1) / math.Cos(r)) lonMin = lon - lonΔ
lonΔ := math.Acos(( math.Cos(r) - math.Sin(latT) * math.Sin(φ1)) / (math.Cos(latT) * math.Cos(φ1) )) lonMax = lon + lonΔ
lonMin := λ1 - lonΔ
lonMax := λ1 + lonΔ
// Adjust for north poll // Adjust for north poll
if latMax > math.Pi/2 { if latMax > math.Pi/2 {
lonMin = -math.Pi lonMin = -math.Pi
latMax = math.Pi/2 latMax = math.Pi/2
lonMax = math.Pi lonMax = math.Pi
} }
// Adjust for south poll // Adjust for south poll
if latMin < -math.Pi/2 { if latMin < -math.Pi/2 {
latMin = -math.Pi/2 latMin = -math.Pi/2
lonMin = -math.Pi lonMin = -math.Pi
lonMax = math.Pi lonMax = math.Pi
} }
// Adjust for wraparound. Remove this if the commented-out condition below this block is added.
if lonMin < -math.Pi || lonMax > math.Pi { if lonMin < -math.Pi || lonMax > math.Pi {
lonMin = -math.Pi lonMin = -math.Pi
lonMax = math.Pi lonMax = math.Pi
} }
/* /*
// Consider splitting into two bboxes and using the below checks and erasing above block for performance. See http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#PolesAnd180thMeridian // Consider splitting area into two bboxes, using the below checks, and erasing above block for performance. See http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates#PolesAnd180thMeridian
// Adjust for wraparound if minimum longitude is less than -180 degrees.
if lonMin < -math.Pi { if lonMin < -math.Pi {
// box 1: // box 1:
latMin = latMin latMin = latMin
@ -243,10 +241,16 @@ func BBoxBounds(lat, lon, meters float64) (float64, float64, float64, float64) {
lonMax = lonMax lonMax = lonMax
} }
// Adjust for wraparound if minimum longitude is greater than -180 degrees.
if lonMax > math.Pi { if lonMax > math.Pi {
// box 1: // box 1:
latMin = latMin
latMax = latMax
lonMin = lonMin
lonMax = -math.Pi lonMax = -math.Pi
// box 2: // box 2:
latMin = latMin
latMax = latMax
lonMin = -math.Pi lonMin = -math.Pi
lonMax -= 2*math.Pi lonMax -= 2*math.Pi
} }