mvt: fix bugs from the mvt merge

bbox.go

@@ -353,15 +353,15 @@ func (e *Extent) Clone() *Extent {
 
 // Intersect will return a new extent that is the intersect of the two extents.
 //
-// +-------------------------+
-// |                         |
-// |       A      +----------+------+
-// |              |//////////|      |
-// |              |/// C ////|      |
-// |              |//////////|      |
-// +--------------+----------+      |
-//                |             B   |
-//                +-----------------+
+//	+-------------------------+
+//	|                         |
+//	|       A      +----------+------+
+//	|              |//////////|      |
+//	|              |/// C ////|      |
+//	|              |//////////|      |
+//	+--------------+----------+      |
+//	               |             B   |
+//	               +-----------------+
 // For example the for the above Box A intersects Box B at the area surround by C.
 //
 // If the Boxes don't intersect does will be false, otherwise ibb will be the intersect.

encoding/mvt/prepare.go

@@ -6,11 +6,14 @@ import (
 	"github.com/go-spatial/geom"
 )
 
-// PrepareGeo converts the geometry's coordinates to tile coordinates. tile should be the
+// PrepareGeo converts the geometry's coordinates to tile pixel coordinates. tile should be the
 // extent of the tile, in the same projection as geo. pixelExtent is the dimension of the
 // (square) tile in pixels usually 4096, see DefaultExtent.
-// The geometry must not go outside the tile extent. If this is unknown,
-// use the clip package before encoding.
+// This function treats the tile extent elements as left, top, right, bottom. This is fine
+// when working with a north-positive projection such as lat/long (epsg:4326)
+// and web mercator (epsg:3857), but a south-positive projection (ie. epsg:2054) or west-postive
+// projection would then flip the geomtery. To properly render these coordinate systems, simply
+// swap the X's or Y's in the tile extent.
 func PrepareGeo(geo geom.Geometry, tile *geom.Extent, pixelExtent float64) geom.Geometry {
 	switch g := geo.(type) {
 	case geom.Point:
@@ -60,10 +63,10 @@ func PrepareGeo(geo geom.Geometry, tile *geom.Extent, pixelExtent float64) geom.
 }
 
 func preparept(g geom.Point, tile *geom.Extent, pixelExtent float64) geom.Point {
-	px := (g.X() - tile.MinX()) / tile.XSpan() * pixelExtent
-	py := (g.Y() - tile.MinY()) / tile.YSpan() * pixelExtent
+	px := int64((g.X() - tile.MinX()) / tile.XSpan() * pixelExtent)
+	py := int64((tile.MaxY() - g.Y()) / tile.YSpan() * pixelExtent)
 
-	return geom.Point{px, py}
+	return geom.Point{float64(px), float64(py)}
 }
 
 func preparelinestr(g geom.LineString, tile *geom.Extent, pixelExtent float64) (ls geom.LineString) {

encoding/mvt/prepare_internal_test.go

@@ -33,28 +33,28 @@ func TestPrepareLinestring(t *testing.T) {
 
 	tests := map[string]tcase{
 		"duplicate pt simple line": {
-			in: geom.LineString{{9.0, 9.0}, {9.0, 9.0}},
-			out: geom.LineString{{9.0, 9.0}, {9.0, 9.0}},
+			in: geom.LineString{{9.0, 4090.0}, {9.0, 4090.0}},
+			out: geom.LineString{{9.0, 6.0}, {9.0, 6.0}},
 			tile: geom.Extent{0.0, 0.0, 4096.0, 4096.0},
 		},
 		"simple line": {
-			in: geom.LineString{{9.0, 9.0}, {11.0, 11.0}},
-			out: geom.LineString{{9.0, 9.0}, {11.0, 11.0}},
+			in: geom.LineString{{9.0, 4090.0}, {11.0, 4091.0}},
+			out: geom.LineString{{9.0, 6.0}, {11.0, 5.0}},
 			tile: geom.Extent{0.0, 0.0, 4096.0, 4096.0},
 		},
 		"edge line": {
 			in: geom.LineString{{0.0, 0.0}, {4096.0, 20.0}},
-			out: geom.LineString{{0.0, 0.0}, {4096.0, 20.0}},
+			out: geom.LineString{{0.0, 4096.0}, {4096.0, 4076.0}},
 			tile: geom.Extent{0.0, 0.0, 4096.0, 4096.0},
 		},
 		"simple line 3pt": {
-			in: geom.LineString{{9.0, 9.0}, {11.0, 9.0}, {11.0, 14.0}},
-			out: geom.LineString{{9.0, 9.0}, {11.0, 9.0}, {11.0, 14.0}},
+			in: geom.LineString{{9.0, 4090.0}, {11.0, 4090.0}, {11.0, 4076.0}},
+			out: geom.LineString{{9.0, 6.0}, {11.0, 6.0}, {11.0, 20.0}},
 			tile: geom.Extent{0.0, 0.0, 4096.0, 4096.0},
 		},
 		"scale" : {
 			in: geom.LineString{{100.0, 100.0}, {300.0, 300.0}},
-			out: geom.LineString{{1024.0, 1024.0}, {3072.0, 3072.0}},
+			out: geom.LineString{{1024.0, 3072.0}, {3072.0, 1024.0}},
 			tile: geom.Extent{0.0, 0.0, 400.0, 400.0},
 		},
 	}

slippy/tile_test.go

@@ -71,14 +71,14 @@ func TestNewTile(t *testing.T) {
 			x:      1,
 			y:      1,
 			buffer: 64,
-			eExtent: geom.NewExtent(
-				[2]float64{-10018754.17, 10018754.17},
-				[2]float64{0, 0},
-			),
-			eBExtent: geom.NewExtent(
-				[2]float64{-1.017529720390625e+07, 1.017529720390625e+07},
-				[2]float64{156543.03390624933, -156543.03390624933},
-			),
+			eExtent: &geom.Extent{
+				-10018754.17, 0,
+				0, 10018754.17,
+			},
+			eBExtent: &geom.Extent{
+				-1.017529720390625e+07, -156543.03390624933,
+				156543.03390624933, 1.017529720390625e+07,
+			},
 			eBounds: spherical.Hull(
 				[2]float64{-90, 66.51},
 				[2]float64{0, 0},
@@ -89,14 +89,14 @@ func TestNewTile(t *testing.T) {
 			x:      11436,
 			y:      26461,
 			buffer: 64,
-			eExtent: geom.NewExtent(
-				[2]float64{-13044437.497219238996, 3856706.6986199953},
-				[2]float64{-13043826.000993041, 3856095.202393799},
-			),
-			eBExtent: geom.NewExtent(
-				[2]float64{-1.3044447051847773e+07, 3.8567162532485295e+06},
-				[2]float64{-1.3043816446364507e+07, 3.856085647765265e+06},
-			),
+			eExtent: &geom.Extent{
+				-13044437.497219238996, 3856095.202393799,
+				-13043826.000993041, 3856706.6986199953,
+			},
+			eBExtent: &geom.Extent{
+				-1.3044447051847773e+07, 3.856085647765265e+06,
+				-1.3043816446364507e+07, 3.8567162532485295e+06,
+			},
 			eBounds: spherical.Hull(
 				[2]float64{-117.18, 32.70},
 				[2]float64{-117.17, 32.70},