90 lines
3.2 KiB
JavaScript
90 lines
3.2 KiB
JavaScript
var _ = require('underscore');
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var BaseDataview = require('../base');
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function BaseOverviewsDataview(query, queryOptions, BaseDataview, queryRewriter, queryRewriteData, options, queries) {
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this.BaseDataview = BaseDataview;
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this.query = query;
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this.queryOptions = queryOptions;
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this.queryRewriter = queryRewriter;
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this.queryRewriteData = queryRewriteData;
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this.options = options;
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this.queries = queries;
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this.baseDataview = new this.BaseDataview(this.query, this.queryOptions, this.queries);
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}
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module.exports = BaseOverviewsDataview;
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BaseOverviewsDataview.prototype = new BaseDataview();
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BaseOverviewsDataview.prototype.constructor = BaseOverviewsDataview;
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// TODO: parameterized these settings
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var SETTINGS = {
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// use overviews as a default fallback strategy
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defaultOverviews: false,
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// minimum ratio of bounding box size to grid size
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// (this would ideally be based on the viewport size in pixels)
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zoomLevelFactor: 1024.0
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};
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// Compute zoom level so that the the resolution grid size of the
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// selected overview is smaller (zoomLevelFactor times smaller at least)
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// than the bounding box size.
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BaseOverviewsDataview.prototype.zoomLevelForBbox = function(bbox) {
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var pxPerTile = 256.0;
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var earthWidth = 360.0;
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// TODO: now we assume overviews are computed for 1-pixel tolerance;
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// should use extended overviews metadata to compute this properly.
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if ( bbox ) {
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var bboxValues = _.map(bbox.split(','), function(v) { return +v; });
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var w = Math.abs(bboxValues[2]-bboxValues[0]);
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var h = Math.abs(bboxValues[3]-bboxValues[1]);
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var maxDim = Math.min(w, h);
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// Find minimum suitable z
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// note that the QueryRewirter will use the minimum level overview
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// of level >= z if it exists, and otherwise the base table
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var z = Math.ceil(-Math.log(maxDim*pxPerTile/earthWidth/SETTINGS.zoomLevelFactor)/Math.log(2.0));
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return Math.max(z, 0);
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}
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return 0;
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};
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BaseOverviewsDataview.prototype.rewrittenQuery = function(query) {
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var zoom_level = this.zoomLevelForBbox(this.options.bbox);
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return this.queryRewriter.query(query, this.queryRewriteData, { zoom_level: zoom_level });
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};
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// Default behaviour
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BaseOverviewsDataview.prototype.defaultSql = function(psql, override, callback) {
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var query = this.query;
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var dataview = this.baseDataview;
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if ( SETTINGS.defaultOverviews ) {
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query = this.rewrittenQuery(query);
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dataview = new this.BaseDataview(query, this.queryOptions);
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}
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return dataview.sql(psql, override, callback);
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};
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// default implementation that can be override in derived classes:
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BaseOverviewsDataview.prototype.sql = function(psql, override, callback) {
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return this.defaultSql(psql, override, callback);
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};
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BaseOverviewsDataview.prototype.search = function(psql, userQuery, callback) {
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return this.baseDataview.search(psql, userQuery, callback);
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};
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BaseOverviewsDataview.prototype.format = function(result) {
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return this.baseDataview.format(result);
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};
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BaseOverviewsDataview.prototype.getType = function() {
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return this.baseDataview.getType();
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};
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BaseOverviewsDataview.prototype.toString = function() {
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return this.baseDataview.toString();
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};
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