浅念
140 lines
3.7 KiB
JavaScript
140 lines
3.7 KiB
JavaScript
/**
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#
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# Copyright 2010 Alexandre Gellibert
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#
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at
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#
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# http://www.apache.org/licenses/LICENSE-2.0
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#
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# Unless required by applicable law or agreed to in writing, software
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# distributed under the License is distributed on an "AS IS" BASIS,
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# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and
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# limitations under the License.
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*/
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var LatLng = require('./LatLng'),
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LatLngBounds = require('./LatLngBounds'),
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GEOCELL_GRID_SIZE = 4,
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GEOCELL_ALPHABET = '0123456789abcdef';
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function computeBox(geocell) {
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var subcell_lng_span, subcell_lat_span;
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var xy, x, y;
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var bbox = _createBoundingBox(90.0, 180.0, -90.0, -180.0);
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while(geocell.length > 0) {
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//geoChar = geocell.charAt(i);
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//pos = GEOCELL_ALPHABET.indexOf(geoChar);
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subcell_lng_span = (bbox.getEast() - bbox.getWest()) / GEOCELL_GRID_SIZE;
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subcell_lat_span = (bbox.getNorth() - bbox.getSouth()) / GEOCELL_GRID_SIZE;
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xy = _subdiv_xy(geocell.charAt(0));
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x = xy[0];
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y = xy[1];
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bbox = _createBoundingBox(bbox.getSouth() + subcell_lat_span * (y + 1),
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bbox.getWest() + subcell_lng_span * (x + 1),
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bbox.getSouth() + subcell_lat_span * y,
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bbox.getWest() + subcell_lng_span * x);
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geocell = geocell.substring(1);
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}
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var sw = new LatLng(bbox.getSouth(), bbox.getWest());
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var ne = new LatLng(bbox.getNorth(), bbox.getEast());
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var bounds = new LatLngBounds(sw, ne);
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return bounds;
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}
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function _createBoundingBox(north, east, south, west) {
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var north_,south_;
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if(south > north) {
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south_ = north;
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north_ = south;
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} else {
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south_ = south;
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north_ = north;
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}
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return {
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northEast: {lat: north_, lng: east},
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southWest: {lat: south_, lng: west},
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getNorth: function() {
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return this.northEast.lat;
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},
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getSouth: function() {
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return this.southWest.lat;
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},
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getWest: function() {
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return this.southWest.lng;
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},
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getEast: function() {
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return this.northEast.lng;
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}
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};
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}
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/**
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* https://code.google.com/p/geomodel/source/browse/trunk/geo/geocell.py#370
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* @param latLng
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* @param resolution
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* @return
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*/
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function getGeocell(lat, lng, resolution) {
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var cell = '';
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var north = 90.0;
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var south = -90.0;
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var east = 180.0;
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var west = -180.0;
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var subcell_lng_span, subcell_lat_span;
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var x, y;
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while(cell.length < resolution + 1) {
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subcell_lng_span = (east - west) / GEOCELL_GRID_SIZE;
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subcell_lat_span = (north - south) / GEOCELL_GRID_SIZE;
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x = Math.min(Math.floor(GEOCELL_GRID_SIZE * (lng - west) / (east - west)), GEOCELL_GRID_SIZE - 1);
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y = Math.min(Math.floor(GEOCELL_GRID_SIZE * (lat - south) / (north - south)),GEOCELL_GRID_SIZE - 1);
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cell += _subdiv_char(x, y);
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south += subcell_lat_span * y;
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north = south + subcell_lat_span;
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west += subcell_lng_span * x;
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east = west + subcell_lng_span;
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}
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return cell;
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}
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/*
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* Returns the (x, y) of the geocell character in the 4x4 alphabet grid.
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*/
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function _subdiv_xy(char) {
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// NOTE: This only works for grid size 4.
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var charI = GEOCELL_ALPHABET.indexOf(char);
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return [(charI & 4) >> 1 | (charI & 1) >> 0,
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(charI & 8) >> 2 | (charI & 2) >> 1];
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}
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/**
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* Returns the geocell character in the 4x4 alphabet grid at pos. (x, y).
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* @return
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*/
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function _subdiv_char(posX, posY) {
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// NOTE: This only works for grid size 4.
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return GEOCELL_ALPHABET.charAt(
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(posY & 2) << 2 |
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(posX & 2) << 1 |
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(posY & 1) << 1 |
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(posX & 1) << 0);
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}
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module.exports = {
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computeBox: computeBox,
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getGeocell: getGeocell
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};
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