Add calculation of max and min zoom for images

These changes:
 - replace the hard coded min/max zoom with values that are calculated
   based on the pixel density of the image and the geo bounds
 - add more implementations of functionality copied from globalmaptiles.py

Author: andrewdodd

go.mod

@@ -2,10 +2,8 @@ module main
 
 require (
 	github.com/ghodss/yaml v1.0.1-0.20190212211648-25d852aebe32
-	github.com/gorilla/handlers v1.4.0 // indirect
 	github.com/gorilla/mux v1.7.0
 	github.com/h2non/bimg v1.0.19
 	golang.org/x/image v0.0.0-20190321063152-3fc05d484e9f
 	gonum.org/v1/gonum v0.0.0-20190330083134-779ef2ac207d
-	gopkg.in/h2non/bimg.v1 v1.0.19
 )

go.sum

@@ -1,7 +1,5 @@
 github.com/ghodss/yaml v1.0.1-0.20190212211648-25d852aebe32 h1:Mn26/9ZMNWSw9C9ERFA1PUxfmGpolnw2v0bKOREu5ew=
 github.com/ghodss/yaml v1.0.1-0.20190212211648-25d852aebe32/go.mod h1:GIjDIg/heH5DOkXY3YJ/wNhfHsQHoXGjl8G8amsYQ1I=
-github.com/gorilla/handlers v1.4.0 h1:XulKRWSQK5uChr4pEgSE4Tc/OcmnU9GJuSwdog/tZsA=
-github.com/gorilla/handlers v1.4.0/go.mod h1:Qkdc/uu4tH4g6mTK6auzZ766c4CA0Ng8+o/OAirnOIQ=
 github.com/gorilla/mux v1.7.0 h1:tOSd0UKHQd6urX6ApfOn4XdBMY6Sh1MfxV3kmaazO+U=
 github.com/gorilla/mux v1.7.0/go.mod h1:1lud6UwP+6orDFRuTfBEV8e9/aOM/c4fVVCaMa2zaAs=
 github.com/h2non/bimg v1.0.19 h1:lrKA2oi4DttnscGeb/oRiBIcRiAX33mmp3yQX8JzGIc=
@@ -10,14 +8,13 @@ golang.org/x/exp v0.0.0-20190125153040-c74c464bbbf2 h1:y102fOLFqhV41b+4GPiJoa0k/
 golang.org/x/exp v0.0.0-20190125153040-c74c464bbbf2/go.mod h1:CJ0aWSM057203Lf6IL+f9T1iT9GByDxfZKAQTCR3kQA=
 golang.org/x/image v0.0.0-20190321063152-3fc05d484e9f h1:FO4MZ3N56GnxbqxGKqh+YTzUWQ2sDwtFQEZgLOxh9Jc=
 golang.org/x/image v0.0.0-20190321063152-3fc05d484e9f/go.mod h1:kZ7UVZpmo3dzQBMxlp+ypCbDeSB+sBbTgSJuh5dn5js=
-golang.org/x/image v0.0.0-20190622003408-7e034cad6442 h1:KHkZ9SH+rcDwdj29lcYkks2agONXqNa8YkEGwGhY6Sg=
 golang.org/x/text v0.3.0/go.mod h1:NqM8EUOU14njkJ3fqMW+pc6Ldnwhi/IjpwHt7yyuwOQ=
 golang.org/x/tools v0.0.0-20190206041539-40960b6deb8e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 gonum.org/v1/gonum v0.0.0-20190330083134-779ef2ac207d h1:ShJE9we+7oZ2ZWS32zNTOntaiKgC3zCnzvTbDLTGZhQ=
 gonum.org/v1/gonum v0.0.0-20190330083134-779ef2ac207d/go.mod h1:2ltnJ7xHfj0zHS40VVPYEAAMTa3ZGguvHGBSJeRWqE0=
+gonum.org/v1/netlib v0.0.0-20190313105609-8cb42192e0e0 h1:OE9mWmgKkjJyEmDAAtGMPjXu+YNeGvK9VTSHY6+Qihc=
 gonum.org/v1/netlib v0.0.0-20190313105609-8cb42192e0e0/go.mod h1:wa6Ws7BG/ESfp6dHfk7C6KdzKA7wR7u/rKwOGE66zvw=
+gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
-gopkg.in/h2non/bimg.v1 v1.0.19 h1:Li7mgBrIvCHvShB4nyCcGJ2Z2rWR/95kgI/U2+U2eYw=
-gopkg.in/h2non/bimg.v1 v1.0.19/go.mod h1:PgsZL7dLwUbsGm1NYps320GxGgvQNTnecMCZqxV11So=
 gopkg.in/yaml.v2 v2.2.2 h1:ZCJp+EgiOT7lHqUV2J862kp8Qj64Jo6az82+3Td9dZw=
 gopkg.in/yaml.v2 v2.2.2/go.mod h1:hI93XBmqTisBFMUTm0b8Fm+jr3Dg1NNxqwp+5A1VGuI=

mapimage/goimage.go

@@ -29,10 +29,7 @@ func NewImageInfo(
 	id,
 	text string,
 	referencePoints []MapImagePair,
-	minZoom int,
-	maxZoom int,
 	contents *os.File) MapImage {
-	//image, err := png.Decode(bytes.NewReader(fileContents))
 	image, _, err := image.Decode(contents)
 	if err != nil {
 		panic(0)
@@ -52,26 +49,32 @@ func NewImageInfo(
 		panic(0)
 	}
 
-	return &goImage{
+	i := goImage{
 		id:              id,
 		text:            text,
-		minZoom:         minZoom,
-		maxZoom:         maxZoom,
+		minZoom:         0,
+		maxZoom:         0,
 		referencePoints: referencePoints,
 		contents:        contents,
 		image:           image,
 		toGeo:           &toGeo,
 		toPixel:         &toPixel,
 	}
 
+	i.minZoom = calculateMinZoom(&i)
+	i.maxZoom = calculateMaxZoom(&i)
+
+	return &i
 }
 
 func (i goImage) Id() string {
 	return i.id
 }
+
 func (i goImage) Text() string {
 	return i.text
 }
+
 func (i goImage) GeoBounds() [2]LatLng {
 	imageSize := i.PixelBounds()
 

mapimage/libvips.go

@@ -34,10 +34,7 @@ func NewVIPSImageInfo(
 	id,
 	text string,
 	referencePoints []MapImagePair,
-	minZoom int,
-	maxZoom int,
 	contents *os.File) MapImage {
-	//image, err := png.Decode(bytes.NewReader(fileContents))
 	imageConfig, format, err := image.DecodeConfig(contents)
 	if err != nil {
 		panic(0)
@@ -64,11 +61,11 @@ func NewVIPSImageInfo(
 		panic(0)
 	}
 
-	return &libvipsImage{
+	i := libvipsImage{
 		id:      id,
 		text:    text,
-		minZoom: minZoom,
-		maxZoom: maxZoom,
+		minZoom: 0,
+		maxZoom: 0,
 		//referencePoints: referencePoints,
 		contents:    contents,
 		fileBuf:     buf,
@@ -77,7 +74,9 @@ func NewVIPSImageInfo(
 		toGeo:       &toGeo,
 		toPixel:     &toPixel,
 	}
-
+	i.minZoom = calculateMinZoom(&i)
+	i.maxZoom = calculateMaxZoom(&i)
+	return &i
 }
 
 func (i libvipsImage) Id() string {

mapimage/main.go

@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"github.com/gorilla/mux"
 	"io"
+	"math"
 	"net/http"
 	"strconv"
 	"strings"
@@ -18,9 +19,12 @@ type MapImage interface {
 	Text() string
 	GeoBounds() [2]LatLng
 	PixelBounds() [2]LatLng
+	// The zoom where whole image is on a single tile?
 	MinZoom() int
+	// The zoom where image is being stretched by more than half?
 	MaxZoom() int
 	//ReferencePoints() []MapImagePair
+	GeoFromPixel(p LatLng) LatLng
 }
 
 type MapImagesSource interface {
@@ -56,6 +60,45 @@ func max(a, b int) int {
 	return b
 }
 
+func calculateMinZoom(i MapImage) int {
+	// The zoom where whole image is on a single tile?
+	geoBounds := i.GeoBounds()
+	geoBoundsMin := geoBounds[0]
+	geoBoundsMax := geoBounds[1]
+
+	for z := 20; z > 0; z-- {
+		minX, minY := LatLonToPixels(geoBoundsMin.Lat, geoBoundsMin.Lng, z)
+		maxX, maxY := LatLonToPixels(geoBoundsMax.Lat, geoBoundsMax.Lng, z)
+		if math.Abs(minX-maxX) < 256 {
+			return z
+		}
+		if math.Abs(minY-maxY) < 256 {
+			return z
+		}
+	}
+
+	return 0
+}
+
+func calculateMaxZoom(i MapImage) int {
+	// The zoom where tiles start to stretch (i.e. pixel density limit)
+	singleTileMin := i.GeoFromPixel(LatLng{Lat: 0, Lng: 0})
+	singleTileMax := i.GeoFromPixel(LatLng{Lat: 256, Lng: 256})
+
+	for z := 0; z < 21; z++ {
+		minX, minY := LatLonToPixels(singleTileMin.Lat, singleTileMin.Lng, z)
+		maxX, maxY := LatLonToPixels(singleTileMax.Lat, singleTileMax.Lng, z)
+		if math.Abs(minX-maxX) > 256 {
+			return z
+		}
+		if math.Abs(minY-maxY) > 256 {
+			return z
+		}
+	}
+
+	return 20
+}
+
 type ApiRepresentation struct {
 	Id          string    `json:"id"`
 	Text        string    `json:"text"`

mapimage/maptile.go

@@ -12,6 +12,7 @@ type TileBounds struct {
 }
 
 const tileSize int64 = 256
+const originShift float64 = 2.0 * math.Pi * 6378137.0 / 2.0
 
 func Resolution(zoom int64) float64 {
 	//"Resolution (meters/pixel) for given zoom level (measured at Equator)"
@@ -22,7 +23,6 @@ func Resolution(zoom int64) float64 {
 
 func PixelsToMeters(px, py, zoom int64) (float64, float64) {
 	//"Converts pixel coordinates in given zoom level of pyramid to EPSG:900913"
-	originShift := 2.0 * math.Pi * 6378137.0 / 2.0
 
 	res := Resolution(zoom)
 	mx := float64(px)*res - originShift
@@ -36,6 +36,33 @@ func (b *TileBounds) FromTile(tx, ty, zoom int64) {
 	b.maxX, b.maxY = PixelsToMeters((tx+1)*tileSize, (ty+1)*tileSize, zoom)
 }
 
+func LatLonToMeters(lat, lon float64) (mx, my float64) {
+	// "Converts given lat/lon in WGS84 Datum to XY in Spherical Mercator EPSG:900913"
+
+	mx = lon * originShift / 180.0
+	my = math.Log(math.Tan((90+lat)*math.Pi/360.0)) / (math.Pi / 180.0)
+	my = my * originShift / 180.0
+	return mx, my
+}
+
+func MetersToPixels(mx, my float64, zoom int64) (px, py float64) {
+	// "Converts EPSG:900913 to pyramid pixel coordinates in given zoom level"
+
+	res := Resolution(zoom)
+	px = (mx + originShift) / float64(res)
+	py = (my + originShift) / float64(res)
+	return px, py
+}
+
+func LatLonToPixels(lat, lon float64, zoom int) (px, py float64) {
+	// "Converts lat/lon to pixel coordinates in given zoom of the EPSG:4326 pyramid"
+
+	res := 180.0 / 256.0 / math.Pow(2, float64(zoom))
+	px = (180.0 + lat) / res
+	py = (90.0 + lon) / res
+	return px, py
+}
+
 func MetersToLatLon(mx, my float64) (float64, float64) {
 	//"Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in WGS84 Datum"
 

serverd.go

@@ -13,6 +13,7 @@ import (
 	"log"
 	"main/mapimage"
 	"net/http"
+	_ "net/http/pprof"
 	"os"
 )
 
@@ -79,6 +80,7 @@ func init() {
 						loadedImage.ReferencePoints,
 						20, 0,
 						f)
+					log.Printf(" >> MinZoom: %v MaxZoom: %v\n", mi.MinZoom(), mi.MaxZoom())
 				}
 				maps.images = append(maps.images, mi)
 			}
@@ -116,6 +118,10 @@ func main() {
 
 	router.PathPrefix("/").Handler(http.FileServer(http.Dir("./ui/build")))
 
+	go func() {
+		log.Println(http.ListenAndServe("localhost:6060", nil))
+	}()
+
 	log.Fatal(http.ListenAndServe(":8000", router))
 
 }