Tile utility code in Java
From Google Mapki
This code is a set of simple methods for converting between lat/lng and google tile references. The zoom levels are API version 1.x Please edit this code if you find any bugs.
import java.awt.Point;
import java.awt.geom.Point2D;
import java.awt.geom.Rectangle2D;
/**
* A set of simple routines to provide information about google tiles (API v1).
* These routines are not written for speed.
* These routines assume a tile size of 256 pixels square.
* Internally a sort of offset mercator projection is used, this places the origin (0,0)
* at the top left and goes to +1,+1 at the bottom right.
* I believe a proper mercator would have 0,0 in the middle and range from -0.5,-0.5 bottom left to +0.5,+0.5 top right.
* I've used this system because it provides a better fit with a typical the pixel coordinate system.
*/
public class GoogleTileUtils {
static int TILE_SIZE = 256;
/**
* Returns the pixel offset of a latitude and longitude within a single typical google tile.
* @param lat
* @param lng
* @param zoom
* @return
*/
public static Point getPixelOffsetInTile(double lat, double lng, int zoom) {
Point pixelCoords = toZoomedPixelCoords(lat, lng, zoom);
return new Point(pixelCoords.x % TILE_SIZE, pixelCoords.y % TILE_SIZE);
}
/**
* returns a Rectangle2D with x = lon, y = lat, width=lonSpan, height=latSpan
* for an x,y,zoom as used by google.
*/
public static Rectangle2D.Double getTileRect(int x, int y, int zoom) {
int tilesAtThisZoom = 1 << (17 - zoom);
double lngWidth = 360.0 / tilesAtThisZoom; // width in degrees longitude
double lng = -180 + (x * lngWidth); // left edge in degrees longitude
double latHeightMerc = 1.0 / tilesAtThisZoom; // height in "normalized" mercator 0,0 top left
double topLatMerc = y * latHeightMerc; // top edge in "normalized" mercator 0,0 top left
double bottomLatMerc = topLatMerc + latHeightMerc;
// convert top and bottom lat in mercator to degrees
// note that in fact the coordinates go from about -85 to +85 not -90 to 90!
double bottomLat = Math.toDegrees((2 * Math.atan(Math.exp(Math.PI * (1 - (2 * bottomLatMerc)))))
- (Math.PI / 2));
double topLat = Math.toDegrees((2 * Math.atan(Math.exp(Math.PI * (1 - (2 * topLatMerc))))) - (Math.PI / 2));
double latHeight = topLat - bottomLat;
return new Rectangle2D.Double(lng, bottomLat, lngWidth, latHeight);
}
/**
* returns the lat/lng as an "Offset Normalized Mercator" pixel coordinate,
* this is a coordinate that runs from 0..1 in latitude and longitude with 0,0 being
* top left. Normalizing means that this routine can be used at any zoom level and
* then multiplied by a power of two to get actual pixel coordinates.
* @param lat in degrees
* @param lng in degrees
* @return
*/
public static Point2D toNormalisedPixelCoords(double lat, double lng) {
// first convert to Mercator projection
// first convert the lat lon to mercator coordintes.
if (lng > 180) {
lng -= 360;
}
lng /= 360;
lng += 0.5;
lat = 0.5 - ((Math.log(Math.tan((Math.PI / 4) + (Math.toRadians(0.5 * lat)))) / Math.PI) / 2.0);
return new Point2D.Double(lng, lat);
}
/**
* returns a point that is a google tile reference for the tile containing the lat/lng and at the zoom level.
* @param lat
* @param lng
* @param zoom
* @return
*/
public static Point toTileXY(double lat, double lng, int zoom) {
Point2D normalised = toNormalisedPixelCoords(lat, lng);
int scale = 1 << (17 - zoom);
// can just truncate to integer, this looses the fractional "pixel offset"
return new Point((int) (normalised.getX() * scale), (int) (normalised.getY() * scale));
}
/**
* returns a point that is a google pixel reference for the particular lat/lng and zoom
* assumes tiles are 256x256.
* @param lat
* @param lng
* @param zoom
* @return
*/
public static Point toZoomedPixelCoords(double lat, double lng, int zoom) {
Point2D normalised = toNormalisedPixelCoords(lat, lng);
double scale = (1 << (17 - zoom)) * TILE_SIZE;
return new Point((int) (normalised.getX() * scale), (int) (normalised.getY() * scale));
}
/**
* Returns a google maps satellite type string for the tile containing the lat and lng at the zoom level.
* @param lat
* @param lng
* @param zoom
* @return
*/
private static String getSatelliteRef(double lat, double lng, int zoom) {
Point tileXY = toTileXY(lat, lng, zoom);
int invZoom = 17 - zoom;
int stepSize = 1 << (17 - zoom);
int currentX = 0;
int currentY = 0;
StringBuffer satString = new StringBuffer(zoom);
satString.append("t");
for (int i = 0; i < invZoom; i++) {
stepSize >>= 1;
if ((currentY + stepSize) > tileXY.y) {
if ((currentX + stepSize) > tileXY.x) {
satString.append('q');
}
else {
currentX += stepSize;
satString.append('r');
}
}
else {
currentY += stepSize;
if ((currentX + stepSize) > tileXY.x) {
satString.append('t');
}
else {
currentX += stepSize;
satString.append('s');
}
}
}
return satString.toString();
}
/** Returns an x,y for a satellite reference
* @param string
* @return
*/
private static Point satelliteRefToTileXY(String satelliteRef) {
// must start with "t"
if ((satelliteRef == null) || (satelliteRef.length() == 0) || (satelliteRef.charAt(0) != 't')) {
throw new RuntimeException("satellite string must start with 't'");
}
int x = 0; // x
int y = 0;
for (int i = 1; i < satelliteRef.length(); i++) {
x <<= 1;
y <<= 1;
char c = satelliteRef.charAt(i);
switch (c) {
case 's':
y += 1;
x += 1;
break;
case 'r':
x += 1;
break;
case 'q':
y += 0;
break;
case 't':
y += 1;
break;
default:
throw new RuntimeException("satellite char '" + c + "' when decoding keyhole string.");
}
}
return new Point(x, y);
}
/**
* Returns the zoom level for the given satellite reference string
* @param string
* @return
*/
private static int satelliteRefToZoom(String satRef) {
return 18 - satRef.length();
}
/**
* Test cases
* @param args
*/
public static void main(String[] args) {
double eps = 1.0e-6;
System.out.println("toNormalizedCoords");
// center
System.out.println("center, expect 0.5,0.5\t" + toNormalisedPixelCoords(0, 0));
// topleft
System.out.println("topLeft, expect 0,0\t" + toNormalisedPixelCoords(85.05113f, -180));
// topright
System.out.println("topRight, expect 1,0\t" + toNormalisedPixelCoords(85.05113f, 180 - eps));
//bottomleft
System.out.println("bottomLeft, expect 0,1\t" + toNormalisedPixelCoords(-85.05113f, -180));
// bottomright
System.out.println("bottomRight, expect 1,1\t" + toNormalisedPixelCoords(-85.05113f, 180 - eps));
// my old home
System.out.println("my old home, expect \t" + toNormalisedPixelCoords(53.427972089896805, -2.2671961784362793));
System.out.println("getTileXY");
System.out.println("center zoom=17, expect 0,0\t" + toTileXY(0, 0, 17));
System.out.println("slightly up right of center zoom=16, expect 1,0\t" + toTileXY(eps, eps, 16));
System.out.println("slightly up right of center zoom=15, expect 2,1\t" + toTileXY(eps, eps, 15));
System.out.println("my old home zoom=0, expect 64710,42436\t"
+ toTileXY(53.427972089896805, -2.2671961784362793, 0));
System.out.println("toPixelCoords");
System.out.println("center zoom=17, expect 127,127\t" + toZoomedPixelCoords(0, 0, 17));
System.out.println("slightly up right of center zoom=16, expect 256,256\t" + toZoomedPixelCoords(eps, eps, 16));
System.out.println("slightly up right of center zoom=15, expect 512,512\t" + toZoomedPixelCoords(eps, eps, 15));
System.out.println("my old home zoom=0, expect 16565898,10863803\t"
+ toZoomedPixelCoords(53.427972089896805, -2.2671961784362793, 0));
System.out.println("getPixelOffsetInTile");
System.out.println("center zoom=17, expect 127,127\t" + getPixelOffsetInTile(0, 0, 17));
System.out.println("slightly up right of center zoom=16, expect 0,0\t" + getPixelOffsetInTile(eps, eps, 16));
System.out.println("slightly up right of center zoom=15, expect 0,0\t" + getPixelOffsetInTile(eps, eps, 15));
System.out.println("my old home zoom=0, expect 138,187\t"
+ getPixelOffsetInTile(53.427972089896805, -2.2671961784362793, 0));
System.out.println("getSatelliteRef");
System.out.println("center zoom=17, expect t\t" + getSatelliteRef(0, 0, 17));
System.out.println("slightly up right of center zoom=16, expect tr\t" + getSatelliteRef(eps, eps, 16));
System.out.println("slightly up right of center zoom=15, expect trt\t" + getSatelliteRef(eps, eps, 15));
System.out.println("my old home zoom=0, expect tqsrsrrsqtssqqqsrq\t"
+ getSatelliteRef(53.427972089896805, -2.2671961784362793, 0));
System.out.println();
System.out.println();
System.out.println("from google to lat/lng");
System.out.println();
System.out.println("satelliteRefToZoom");
System.out.println("expect 17\t" + satelliteRefToZoom("t"));
System.out.println("expect 16\t" + satelliteRefToZoom("tr"));
System.out.println("expect 15\t" + satelliteRefToZoom("trt"));
System.out.println("expect 0\t" + satelliteRefToZoom("tqsrsrrsqtssqqqsrq"));
System.out.println("satelliteRefToTileXY");
System.out.println("expect 0,0\t" + satelliteRefToTileXY("t"));
System.out.println("expect 1,0\t" + satelliteRefToTileXY("tr"));
System.out.println("expect 2,1\t" + satelliteRefToTileXY("trt"));
System.out.println("expect 64710,42436\t" + satelliteRefToTileXY("tqsrsrrsqtssqqqsrq"));
System.out.println("tileXYToRectangle");
System.out.println("expect -180,-85,360,170\t" + getTileRect(0, 0, 17));
System.out.println("expect 0,0,180,85\t" + getTileRect(1, 0, 16));
System.out.println("expect 0,0,90,66.5\t" + getTileRect(2, 1, 15));
System.out.println("expect -2.268677,53.42754, 0.002747,0.00163\t" + getTileRect(64710, 42436, 0));
}
}
