gibs.js

/**
* GIBS Web Examples
*
* Copyright 2013 - 2020 United States Government as represented by the
* Administrator of the National Aeronautics and Space Administration.
* All Rights Reserved.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
*    http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/

var gibs = {};

gibs.GeographicTilingScheme = function (options) {
  var self = new Cesium.GeographicTilingScheme(options);
  var Math = Cesium.Math;

  var tilePixels = 512;
  var rectangle = Cesium.Rectangle.MAX_VALUE;

  // Resolution: radians per pixel
  var levels = [
    { width: 2, height: 1, resolution: 0.009817477042468103 },
    { width: 3, height: 2, resolution: 0.004908738521234052 },
    { width: 5, height: 3, resolution: 0.002454369260617026 },
    { width: 10, height: 5, resolution: 0.001227184630308513 },
    { width: 20, height: 10, resolution: 0.0006135923151542565 },
    { width: 40, height: 20, resolution: 0.00030679615757712823 },
    { width: 80, height: 40, resolution: 0.00015339807878856412 },
    { width: 160, height: 80, resolution: 0.00007669903939428206 },
    { width: 320, height: 160, resolution: 0.00003834951969714103 }
  ];

  self.getNumberOfXTilesAtLevel = function (level) {
    return levels[level].width;
  };

  self.getNumberOfYTilesAtLevel = function (level) {
    return levels[level].height;
  };

  self.tileXYToRectangle = function (x, y, level, result) {
    var resolution = levels[level].resolution;

    var xTileWidth = resolution * tilePixels;
    var west = x * xTileWidth + rectangle.west;
    var east = (x + 1) * xTileWidth + rectangle.west;

    var yTileHeight = resolution * tilePixels;
    var north = rectangle.north - y * yTileHeight;
    var south = rectangle.north - (y + 1) * yTileHeight;

    if (!result) {
      result = new Cesium.Rectangle(0, 0, 0, 0);
    }
    result.west = west;
    result.south = south;
    result.east = east;
    result.north = north;
    return result;
  };

  self.positionToTileXY = function (position, level, result) {
    if (!Cesium.Rectangle.contains(rectangle, position)) {
      return undefined;
    }

    var xTiles = levels[level].width;
    var yTiles = levels[level].height;
    var resolution = levels[level].resolution;

    var xTileWidth = resolution * tilePixels;
    var yTileHeight = resolution * tilePixels;

    var longitude = position.longitude;
    if (rectangle.east < rectangle.west) {
      longitude += Math.TWO_PI;
    }

    var xTileCoordinate = (longitude - rectangle.west) / xTileWidth | 0;
    if (xTileCoordinate >= xTiles) {
      xTileCoordinate = xTiles - 1;
    }

    var latitude = position.latitude;
    var yTileCoordinate = (rectangle.north - latitude) / yTileHeight | 0;
    if (yTileCoordinate > yTiles) {
      yTileCoordinate = yTiles - 1;
    }

    if (!result) {
      result = new Cesium.Cartesian2(0, 0);
    }
    result.x = xTileCoordinate;
    result.y = yTileCoordinate;
    return result;
  };

  return self;
};