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Aug 18, 2015
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var util = require("util");
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var Promise = require("bluebird"),
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Map = require("collections/map"),
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_ = require("underscore");
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// Used to build up a set of hierarchical VRTs.
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// The problem with VRTs that have many, many files is...they are sloooow.
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// This uses a technique of building VRTs up so that they do not contain
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// more images than some threshold. If the original set of images
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// is greater than the the threshold, then we build VRTs in a grid based
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// on the min/max col and row of the grid coordinates.
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// Then those VRTs that we built up are contructed into another VRT.
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// This is recursive, so if it ends up that the generated set of VRTs in the first
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// level make up more images then the threshold, those images will be partitioned
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// into another level's VRT, and so one, until the last VRT has no more images
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// then the threshold.
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// Requires that you set "this" to a swfr DeciderContext.
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module.exports = function buildHierarchicalVrt(initialCoordsAndFiles, vrtPath, options) {
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var threshold = options.vrtThreshold | 256;
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var t = Math.sqrt(threshold) | 0;
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var levelUpHierarchy = function(level, desc) {
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var minCol = desc.minCol,
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minRow = desc.minRow;
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var coordsAndFiles = desc.coordsAndFiles;
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var newMinCol = -1,
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newMinRow = -1;
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var m = new Map();
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for(var i = 0; i < coordsAndFiles.length; i += 1) {
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var caf = coordsAndFiles[i];
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var coord = caf.coord;
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if(coord[0] < newMinCol || newMinCol < 0) { newMinCol = coord[0]; }
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if(coord[1] < newMinRow || newMinRow < 0) { newMinRow = coord[1]; }
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var file = caf.file;
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var x = (coord[0] - minCol) / t | 0;
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var y = (coord[1] - minRow) / t | 0;
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var s = x + "-" + y;
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if(!m.has(s)) { m.set(s, { coord: [x, y], componentFiles: [], file: util.format("%s-%d-%s.vrt", vrtPath, level,s) }); }
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m.get(s).componentFiles.push(file);
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}
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return {
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minCol: newMinCol,
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minRow: newMinRow,
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coordsAndFiles: m.values()
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};
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};
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var minCol = -1,
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minRow = -1;
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_.forEach(_.map(initialCoordsAndFiles, function(caf) { return caf.coord; }), function(coord) {
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if(coord[0] < minCol || minCol < 0) { minCol = coord[0]; }
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if(coord[1] < minRow || minRow < 0) { minRow = coord[1]; }
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});
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var desc = {
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minCol: minCol,
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minRow: minRow,
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coordsAndFiles: initialCoordsAndFiles
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};
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var level = 1;
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var vrtSteps = [];
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while(desc.coordsAndFiles.length > threshold) {
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desc = levelUpHierarchy(level, desc);
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var vrtStep = _.map(desc.coordsAndFiles, function(caf) { return { vrtPath: caf.file, componentFiles: caf.componentFiles } });
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vrtSteps.push(vrtStep);
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level += 1;
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}
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vrtSteps.push([{ vrtPath: vrtPath, componentFiles: _.map(desc.coordsAndFiles, function(caf) { return caf.file; }) }]);
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return Promise
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.resolve(vrtSteps)
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.bind(this)
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.each(function(vrtStep) {
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return Promise
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.resolve(vrtStep)
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.bind(this)
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.map(function(vrtBuildDesc) {
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return this.activity("buildVRT", "1.0", vrtBuildDesc.componentFiles, vrtBuildDesc.vrtPath, { nodata: 0 });
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});
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})
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.then(function() {
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return vrtPath;
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});
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};