ogc-parser.js

'use strict';

const assert = {
	strictEqual( actual, expected, ...args ) {

		args = args || [];
		if ( actual !== expected ) {

			throw new Error( `${actual} (actual) should equal ${expected} (expected): ${[ ...args ].join( ' ' )}` );

		}

	},
	notStrictEqual( actual, expected, ...args ) {

		args = args || [];
		if ( actual === expected ) {

			throw new Error( `${actual} (actual) should NOT equal ${expected} (expected): ${[ ...args ].join( ' ' )}` );

		}

	},
};

/*
function dumpBuf(buf) {
  for (let i = 0; i < buf.length; i += 32) {
    const p = [];
    const a = [];
    for (let j = i; j < i + 32 && j < buf.length; ++j) {
      const b = buf[j];
      p.push(b.toString(16).padStart(2, '0'));
      a.push(b >= 32 && b < 128 ? String.fromCharCode(b) : '.');
      if (j % 4 === 3) {
        p.push(' ');
      }
    }
    console.log(i.toString(16).padStart(8, '0'), ':', p.join(''), a.join(''));
  }
}
*/

function parse( buf ) {

	assert.strictEqual( buf[ 0 ], 0x47, 'bad header' );
	assert.strictEqual( buf[ 1 ], 0x50, 'bad header' );
	assert.strictEqual( buf[ 2 ], 0, 'unknown version' ); // version
	const flags = buf[ 3 ];

	const flag_x = ( flags >> 5 ) & 1;
	// const flag_empty_geo = (flags >> 4) & 1;  // 1 = empty, 0 non-empty
	const flag_byteOrder = ( flags >> 0 ) & 1; // 1 = little endian, 0 = big
	const flag_envelope = ( flags >> 1 ) & 7;

	assert.strictEqual( flag_x, 0, 'x must be 0' );

	const envelopeSizes = [
		0, // 0: non
		4, // 1: minx, maxx, miny, maxy
		6, // 2: minx, maxx, miny, maxy, minz, maxz
		6, // 3: minx, maxx, miny, maxy, minm, maxm
		8, // 4: minx, maxx, miny, maxy, minz, maxz, minm, maxm
	];

	const envelopeSize = envelopeSizes[ flag_envelope ];
	assert.notStrictEqual( envelopeSize, undefined );

	const headerSize = 8;
	let cursor = headerSize;

	const dataView = new DataView( buf.buffer );
	/*
  const readBE = {
    getDouble() { const v = buf.readDoubleBE(cursor); cursor += 8 ; return v; },
    getFloat()  { const v = buf.readFloatBE(cursor);  cursor += 4 ; return v; },
    getInt8()   { const v = buf.readInt8(cursor);     cursor += 1 ; return v; },
    getUint8()  { const v = buf.readUInt8(cursor);    cursor += 1 ; return v; },
    getInt16()  { const v = buf.readInt16BE(cursor);  cursor += 2 ; return v; },
    getUint16() { const v = buf.readUInt16BE(cursor); cursor += 2 ; return v; },
    getInt32()  { const v = buf.readInt32BE(cursor);  cursor += 4 ; return v; },
    getUint32() { const v = buf.readUInt32BE(cursor); cursor += 4 ; return v; },
  };

  const readLE = {
    getDouble() { const v = buf.readDoubleLE(cursor); cursor += 8 ; return v; },
    getFloat()  { const v = buf.readFloatLE(cursor);  cursor += 4 ; return v; },
    getInt8()   { const v = buf.readInt8(cursor);     cursor += 1 ; return v; },
    getUint8()  { const v = buf.readUInt8(cursor);    cursor += 1 ; return v; },
    getInt16()  { const v = buf.readInt16LE(cursor);  cursor += 2 ; return v; },
    getUint16() { const v = buf.readUInt16LE(cursor); cursor += 2 ; return v; },
    getInt32()  { const v = buf.readInt32LE(cursor);  cursor += 4 ; return v; },
    getUint32() { const v = buf.readUInt32LE(cursor); cursor += 4 ; return v; },
  };
  */

	let littleEndian;
	const endianStack = [];

	function pushByteOrder( byteOrder ) {

		endianStack.push( littleEndian );
		littleEndian = byteOrder;

	}

	function popByteOrder() {

		littleEndian = endianStack.pop();

	}

	const getDouble = () => {

		const v = dataView.getFloat64( cursor, littleEndian ); cursor += 8; return v;

	};

	// const getFloat =  () => { const v = dataView.getFloat32(cursor, littleEndian); cursor += 4 ; return v; };
	const getInt8 = () => {

		const v = dataView.getInt8( cursor ); cursor += 1; return v;

	};

	// const getUint8 =  () => { const v = dataView.getUint8(cursor, littleEndian);   cursor += 1 ; return v; };
	// const getInt16 =  () => { const v = dataView.getInt16(cursor, littleEndian);   cursor += 2 ; return v; };
	// const getUint16 = () => { const v = dataView.getUint16(cursor, littleEndian);  cursor += 2 ; return v; };
	// const getInt32 =  () => { const v = dataView.getInt32(cursor, littleEndian);   cursor += 4 ; return v; };
	const getUint32 = () => {

		const v = dataView.getUint32( cursor, littleEndian ); cursor += 4; return v;

	};

	pushByteOrder( flag_byteOrder );

	const envelope = [];
	for ( let i = 0; i < envelopeSize; ++ i ) {

		envelope.push( getDouble() );

	}

	const primitives = [];

	function getPoints( num ) {

		const points = [];
		for ( let i = 0; i < num; ++ i ) {

			points.push( getDouble(), getDouble() );

		}

		return points;

	}

	function getRings( num ) {

		const rings = [];
		for ( let i = 0; i < num; ++ i ) {

			rings.push( getPoints( getUint32() ) );

		}

		return rings;

	}

	function pointHandler() {

		return {
			type: 'point',
			point: getPoints( 1 ),
		};

	}

	function lineStringHandler() {

		return {
			type: 'lineString',
			points: getPoints( getUint32() ),
		};

	}

	function polygonHandler() {

		return {
			type: 'polygon',
			rings: getRings( getUint32() ),
		};

	}

	function multiPointHandler() {

		// WTF?
		const points = [];
		const num = getUint32();
		for ( let i = 0; i < num; ++ i ) {

			pushByteOrder( getInt8() );
			const type = getUint32();
			assert.strictEqual( type, 1 ); // must be point
			points.push( getDouble(), getDouble() );
			popByteOrder();

		}

		return {
			type: 'multiPoint',
			points,
		};

	}

	function multiLineStringHandler() {

		// WTF?
		const lineStrings = [];
		const num = getUint32();
		for ( let i = 0; i < num; ++ i ) {

			pushByteOrder( getInt8() );
			const type = getUint32();
			assert.strictEqual( type, 2 ); // must be lineString
			lineStrings.push( getPoints( getUint32() ) );
			popByteOrder();

		}

		return {
			type: 'multiLineString',
			lineStrings,
		};

	}

	function multiPolygonHandler() {

		// WTF?
		const polygons = [];
		const num = getUint32();
		for ( let i = 0; i < num; ++ i ) {

			pushByteOrder( getInt8() );
			const type = getUint32();
			assert.strictEqual( type, 3 ); // must be polygon
			polygons.push( getRings( getUint32() ) );
			popByteOrder();

		}

		return {
			type: 'multiPolygon',
			polygons,
		};

	}

	const typeHandlers = [
		undefined, // 0
		pointHandler, // 1
		lineStringHandler, // 2
		polygonHandler, // 3
		multiPointHandler, // 4
		multiLineStringHandler, // 5,
		multiPolygonHandler, // 6,
	];

	const end = buf.length;
	while ( cursor < end ) {

		pushByteOrder( getInt8() );
		const type = getUint32();
		const handler = typeHandlers[ type ];
		assert.notStrictEqual( handler, undefined, 'unknown type' );
		primitives.push( handler() );
		popByteOrder();

	}

	return {
		envelope,
		primitives,
	};

}

window.ogcParser = { parse };