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Faster point in polygon / GeoJSON updates
The big change is that the GeoJSON package has been completely rewritten to fix a few of geometry calculation bugs, increase performance, and to better follow the GeoJSON spec RFC 7946. GeoJSON updates - A LineString now requires at least two points. - All json members, even foreign, now persist with the object. - The bbox member persists too but is no longer used for geometry calculations. This is change in behavior. Previously Tile38 would treat the bbox as the object's physical rectangle. - Corrections to geometry intersects and within calculations. Faster spatial queries - The performance of Point-in-polygon and object intersect operations are greatly improved for complex polygons and line strings. It went from O(n) to roughly O(log n). - The same for all collection types with many children, including FeatureCollection, GeometryCollection, MultiPoint, MultiLineString, and MultiPolygon. Codebase changes - The pkg directory has been renamed to internal - The GeoJSON internal package has been moved to a seperate repo at https://github.com/tidwall/geojson. It's now vendored. Please look out for higher memory usage for datasets using complex shapes. A complex shape is one that has 64 or more points. For these shapes it's expected that there will be increase of least 54 bytes per point.
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,142 @@ | ||
| package clip | ||
|
|
||
| import ( | ||
| "github.com/tidwall/geojson" | ||
| "github.com/tidwall/geojson/geometry" | ||
| ) | ||
|
|
||
| // Clip clips the contents of a geojson object and return | ||
| func Clip(obj geojson.Object, clipper geojson.Object) (clipped geojson.Object) { | ||
| switch obj := obj.(type) { | ||
| case *geojson.Point: | ||
| return clipPoint(obj, clipper) | ||
| case *geojson.Rect: | ||
| return clipRect(obj, clipper) | ||
| case *geojson.LineString: | ||
| return clipLineString(obj, clipper) | ||
| case *geojson.Polygon: | ||
| return clipPolygon(obj, clipper) | ||
| case *geojson.Feature: | ||
| return clipFeature(obj, clipper) | ||
| case geojson.Collection: | ||
| return clipCollection(obj, clipper) | ||
| } | ||
| return obj | ||
| } | ||
|
|
||
| // clipSegment is Cohen-Sutherland Line Clipping | ||
| // https://www.cs.helsinki.fi/group/goa/viewing/leikkaus/lineClip.html | ||
| func clipSegment(seg geometry.Segment, rect geometry.Rect) ( | ||
| res geometry.Segment, rejected bool, | ||
| ) { | ||
| startCode := getCode(rect, seg.A) | ||
| endCode := getCode(rect, seg.B) | ||
| if (startCode | endCode) == 0 { | ||
| // trivially accept | ||
| res = seg | ||
| } else if (startCode & endCode) != 0 { | ||
| // trivially reject | ||
| rejected = true | ||
| } else if startCode != 0 { | ||
| // start is outside. get new start. | ||
| newStart := intersect(rect, startCode, seg.A, seg.B) | ||
| res, rejected = | ||
| clipSegment(geometry.Segment{A: newStart, B: seg.B}, rect) | ||
| } else { | ||
| // end is outside. get new end. | ||
| newEnd := intersect(rect, endCode, seg.A, seg.B) | ||
| res, rejected = clipSegment(geometry.Segment{A: seg.A, B: newEnd}, rect) | ||
| } | ||
| return | ||
| } | ||
|
|
||
| // clipRing is Sutherland-Hodgman Polygon Clipping | ||
| // https://www.cs.helsinki.fi/group/goa/viewing/leikkaus/intro2.html | ||
| func clipRing(ring []geometry.Point, bbox geometry.Rect) ( | ||
| resRing []geometry.Point, | ||
| ) { | ||
| if len(ring) < 4 { | ||
| // under 4 elements this is not a polygon ring! | ||
| return | ||
| } | ||
| var edge uint8 | ||
| var inside, prevInside bool | ||
| var prev geometry.Point | ||
| for edge = 1; edge <= 8; edge *= 2 { | ||
| prev = ring[len(ring)-2] | ||
| prevInside = (getCode(bbox, prev) & edge) == 0 | ||
| for _, p := range ring { | ||
| inside = (getCode(bbox, p) & edge) == 0 | ||
| if prevInside && inside { | ||
| // Staying inside | ||
| resRing = append(resRing, p) | ||
| } else if prevInside && !inside { | ||
| // Leaving | ||
| resRing = append(resRing, intersect(bbox, edge, prev, p)) | ||
| } else if !prevInside && inside { | ||
| // Entering | ||
| resRing = append(resRing, intersect(bbox, edge, prev, p)) | ||
| resRing = append(resRing, p) | ||
| } else { | ||
| // Staying outside | ||
| } | ||
| prev, prevInside = p, inside | ||
| } | ||
| if len(resRing) > 0 && resRing[0] != resRing[len(resRing)-1] { | ||
| resRing = append(resRing, resRing[0]) | ||
| } | ||
| ring, resRing = resRing, []geometry.Point{} | ||
| if len(ring) == 0 { | ||
| break | ||
| } | ||
| } | ||
| resRing = ring | ||
| return | ||
| } | ||
|
|
||
| func getCode(bbox geometry.Rect, point geometry.Point) (code uint8) { | ||
| code = 0 | ||
|
|
||
| if point.X < bbox.Min.X { | ||
| code |= 1 // left | ||
| } else if point.X > bbox.Max.X { | ||
| code |= 2 // right | ||
| } | ||
|
|
||
| if point.Y < bbox.Min.Y { | ||
| code |= 4 // bottom | ||
| } else if point.Y > bbox.Max.Y { | ||
| code |= 8 // top | ||
| } | ||
|
|
||
| return | ||
| } | ||
|
|
||
| func intersect(bbox geometry.Rect, code uint8, start, end geometry.Point) ( | ||
| new geometry.Point, | ||
| ) { | ||
| if (code & 8) != 0 { // top | ||
| new = geometry.Point{ | ||
| X: start.X + (end.X-start.X)*(bbox.Max.Y-start.Y)/(end.Y-start.Y), | ||
| Y: bbox.Max.Y, | ||
| } | ||
| } else if (code & 4) != 0 { // bottom | ||
| new = geometry.Point{ | ||
| X: start.X + (end.X-start.X)*(bbox.Min.Y-start.Y)/(end.Y-start.Y), | ||
| Y: bbox.Min.Y, | ||
| } | ||
| } else if (code & 2) != 0 { //right | ||
| new = geometry.Point{ | ||
| X: bbox.Max.X, | ||
| Y: start.Y + (end.Y-start.Y)*(bbox.Max.X-start.X)/(end.X-start.X), | ||
| } | ||
| } else if (code & 1) != 0 { // left | ||
| new = geometry.Point{ | ||
| X: bbox.Min.X, | ||
| Y: start.Y + (end.Y-start.Y)*(bbox.Min.X-start.X)/(end.X-start.X), | ||
| } | ||
| } else { // should not call intersect with the zero code | ||
| } | ||
|
|
||
| return | ||
| } |
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