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Haoming Yin
8f93956ff1
- From zoom level 20 to 1, once find a size that contains the whole boundary, then the size will be used to retrieve map image from google #story[928]
53 lines
2.0 KiB
Java
53 lines
2.0 KiB
Java
package seng302.models.map;
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/**
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* An utility class useful to convert between Geo locations and Mercator projection
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* planar coordinates.
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* Created by Haoming on 15/5/2017
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*/
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public class MercatorProjection {
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private static final double MERCATOR_RANGE = 256;
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private static final double pixelsPerLngDegree = MERCATOR_RANGE / 360.0;
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private static final double pixelsPerLngRadian = MERCATOR_RANGE / (2 * Math.PI);
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/**
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* A help function keeps the value in bound between -0.9999 and 0.9999.
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* @param value in bound value
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* @return the value in bound
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*/
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private static double bound(double value) {
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return Math.min(Math.max(value, -0.9999), 0.9999);
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}
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/**
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* Projects a Geo Location (lat, lng) on a planar
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* @param geo MapGeo (lat, lng) location to be projected
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* @return the projection GeoPoint (x, y) on planar
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*/
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public static MapPoint toMapPoint(MapGeo geo) {
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MapPoint point = new MapPoint(0, 0);
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MapPoint origin = new MapPoint(MERCATOR_RANGE / 2.0, MERCATOR_RANGE / 2.0);
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point.setX(origin.getX() + geo.getLng() * pixelsPerLngDegree);
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// NOTE(appleton): Truncating to 0.9999 effectively limits latitude to
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// 89.189. This is about a third of a tile past the edge of the world tile.
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double sinY = bound(Math.sin(Math.toRadians(geo.getLat())));
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point.setY(origin.getY() + 0.5 * Math.log((1 + sinY) / (1 - sinY)) * (-pixelsPerLngRadian));
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return point;
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}
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/**
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* Converts the planar projection (x, y) back to Geo Location (lat, lng)
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* @param point MapPoint (x, y) to be converted back
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* @return the original Geo location converted from the given projection point
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*/
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public static MapGeo toMapGeo(MapPoint point) {
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MapPoint origin = new MapPoint(MERCATOR_RANGE / 2.0, MERCATOR_RANGE / 2.0);
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double lng = (point.getX() - origin.getX()) / pixelsPerLngDegree;
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double latRadians = (point.getY() - origin.getY()) / (-pixelsPerLngRadian);
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double lat = Math.toDegrees(2 * Math.atan(Math.exp(latRadians)) - Math.PI / 2.0);
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return new MapGeo(lat, lng);
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}
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}
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