48 lines
1.6 KiB
JavaScript
48 lines
1.6 KiB
JavaScript
var stream = require('stream');
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var util = require('util');
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module.exports = ZXYStream;
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util.inherits(ZXYStream, stream.Readable);
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// Readable stream of line-delimited z/x/y coordinates
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// contained within the MBTiles `tiles` table/view.
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//
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// The `batch` option exists to allow tests to check that
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// multiple calls to `_read` are handled properly. IRL the
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// default offset of 10000 should be reasonably efficient
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// and not worth messing with.
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function ZXYStream(source, options) {
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if (!source) throw new TypeError('MBTiles source required');
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options = options || {};
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if (options.batch !== undefined && typeof options.batch !== 'number')
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throw new TypeError('options.batch must be a positive integer');
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this.source = source;
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this.batch = options.batch || 10000;
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this.offset = 0;
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stream.Readable.call(this);
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}
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ZXYStream.prototype._read = function() {
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var stream = this;
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this.source._db.all('SELECT zoom_level AS z, tile_column AS x, tile_row AS y FROM tiles LIMIT ' + this.batch + ' OFFSET ' + this.offset, function(err, rows) {
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if (err && err.code === 'SQLITE_ERROR' && /no such table/.test(err.message)) return stream.push(null);
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if (err) return stream.emit('error', err);
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if (!rows.length) return stream.push(null);
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stream.offset += stream.batch;
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var chunk = '';
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for (var i = 0; i < rows.length; i++) chunk += toLine(rows[i]);
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stream.push(chunk);
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});
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};
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function toLine(row) {
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// Flip Y coordinate because MBTiles files are TMS.
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var y = row.y = (1 << row.z) - 1 - row.y;
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return row.z + '/' + row.x + '/' + y + '\n';
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}
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