openlaysers开发常见坐标定义说明
README
最近在了解openlayers定义投影的一些机制，这边简单做一个记录，自我总结下。在ol中默认自带的定义投影坐标为EPSG:4326和EPSG:3857，同时ol也支持proj4进行相关投影坐标信息的扩招，详细的后面可以做个简单的示例。
1.BD09
bd09是百度在gcj02加偏基础，再进行加密的一种火星投影坐标系，在ol中明显是不存在对火星投影的定义，这里我们需要使用百度的相关图层，需要按照一定的投影行列规则进行数据的请求，下面是在ol中对bd09进行定义的相关操作代码：
var forEachPoint = function(func) {
return function(input, opt_output, opt_dimension) {
var len = input.length;
var dimension = opt_dimension ? opt_dimension: 2;
var output;
if (opt_output) {
output = opt_output
} else {
if (dimension !== 2) {
output = input.slice()
} else {
output = new Array(len)
}
}
for (var offset = 0; offset < len; offset += dimension) {
func(input, output, offset)
}
return output
}
};
var sphericalMercator = {};
var RADIUS = 6378137;
var MAX_LATITUDE = 85.0511287798;
var RAD_PER_DEG = Math.PI / 180;
sphericalMercator.forward = forEachPoint(function(input, output, offset) {
var lat = Math.max(Math.min(MAX_LATITUDE, input[offset + 1]), -MAX_LATITUDE);
var sin = Math.sin(lat * RAD_PER_DEG);
output[offset] = RADIUS * input[offset] * RAD_PER_DEG;
output[offset + 1] = RADIUS * Math.log((1 + sin) / (1 - sin)) / 2
});
sphericalMercator.inverse = forEachPoint(function(input, output, offset) {
output[offset] = input[offset] / RADIUS / RAD_PER_DEG;
output[offset + 1] = (2 * Math.atan(Math.exp(input[offset + 1] / RADIUS)) - (Math.PI / 2)) / RAD_PER_DEG
});
var baiduMercator = {};
var MCBAND = [12890594.86, 8362377.87, 5591021, 3481989.83, 1678043.12, 0];
var LLBAND = [75, 60, 45, 30, 15, 0];
var MC2LL = [[1.410526172116255e-8, 0.00000898305509648872, -1.9939833816331, 200.9824383106796, -187.2403703815547, 91.6087516669843, -23.38765649603339, 2.57121317296198, -0.03801003308653, 17337981.2], [ - 7.435856389565537e-9, 0.000008983055097726239, -0.78625201886289, 96.32687599759846, -1.85204757529826, -59.36935905485877, 47.40033549296737, -16.50741931063887, 2.28786674699375, 10260144.86], [ - 3.030883460898826e-8, 0.00000898305509983578, 0.30071316287616, 59.74293618442277, 7.357984074871, -25.38371002664745, 13.45380521110908, -3.29883767235584, 0.32710905363475, 6856817.37], [ - 1.981981304930552e-8, 0.000008983055099779535, 0.03278182852591, 40.31678527705744, 0.65659298677277, -4.44255534477492, 0.85341911805263, 0.12923347998204, -0.04625736007561, 4482777.06], [3.09191371068437e-9, 0.000008983055096812155, 0.00006995724062, 23.10934304144901, -0.00023663490511, -0.6321817810242, -0.00663494467273, 0.03430082397953, -0.00466043876332, 2555164.4], [2.890871144776878e-9, 0.000008983055095805407, -3.068298e-8, 7.47137025468032, -0.00000353937994, -0.02145144861037, -0.00001234426596, 0.00010322952773, -0.00000323890364, 826088.5]];
var LL2MC = [[ - 0.0015702102444, 111320.7020616939, 1704480524535203, -10338987376042340, 26112667856603880, -35149669176653700, 26595700718403920, -10725012454188240, 1800819912950474, 82.5], [0.0008277824516172526, 111320.7020463578, 647795574.6671607, -4082003173.641316, 10774905663.51142, -15171875531.51559, 12053065338.62167, -5124939663.577472, 913311935.9512032, 67.5], [0.00337398766765, 111320.7020202162, 4481351.045890365, -23393751.19931662, 79682215.47186455, -115964993.2797253, 97236711.15602145, -43661946.33752821, 8477230.501135234, 52.5], [0.00220636496208, 111320.7020209128, 51751.86112841131, 3796837.749470245, 992013.7397791013, -1221952.21711287, 1340652.697009075, -620943.6990984312, 144416.9293806241, 37.5], [ - 0.0003441963504368392, 111320.7020576856, 278.2353980772752, 2485758.690035394, 6070.750963243378, 54821.18345352118, 9540.606633304236, -2710.55326746645, 1405.483844121726, 22.5], [ - 0.0003218135878613132, 111320.7020701615, 0.00369383431289, 823725.6402795718, 0.46104986909093, 2351.343141331292, 1.58060784298199, 8.77738589078284, 0.37238884252424, 7.45]];
function getRange(v, min, max) {
v = Math.max(v, min);
v = Math.min(v, max);
return v
}
function getLoop(v, min, max) {
var d = max - min;
while (v > max) {
v -= d
}
while (v < min) {
v += d
}
return v
}
function convertor(input, output, offset, table) {
var px = input[offset];
var py = input[offset + 1];
var x = table[0] + table[1] * Math.abs(px);
var d = Math.abs(py) / table[9];
var y = table[2] + table[3] * d + table[4] * d * d + table[5] * d * d * d + table[6] * d * d * d * d + table[7] * d * d * d * d * d + table[8] * d * d * d * d * d * d;
output[offset] = x * (px < 0 ? -1 : 1);
output[offset + 1] = y * (py < 0 ? -1 : 1)
}
baiduMercator.forward = forEachPoint(function(input, output, offset) {
var lng = getLoop(input[offset], -180, 180);
var lat = getRange(input[offset + 1], -74, 74);
var table = null;
var j;
for (j = 0; j < LLBAND.length; ++j) {
if (lat >= LLBAND[j]) {
table = LL2MC[j];
break
}
}
if (table === null) {
for (j = LLBAND.length - 1; j >= 0; --j) {
if (lat <= -LLBAND[j]) {
table = LL2MC[j];
break
}
}
}
output[offset] = lng;
output[offset + 1] = lat;
convertor(output, output, offset, table)
});
baiduMercator.inverse = forEachPoint(function(input, output, offset) {
var y_abs = Math.abs(input[offset + 1]);
var table = null;
for (var j = 0; j < MCBAND.length; j++) {
if (y_abs >= MCBAND[j]) {
table = MC2LL[j];
break
}
}
convertor(input, output, offset, table)
});
var gcj02 = {};
var PI = Math.PI;
var AXIS = 6378245.0;
var OFFSET = 0.00669342162296594323;
function delta(wgLon, wgLat) {
var dLat = transformLat(wgLon - 105.0, wgLat - 35.0);
var dLon = transformLon(wgLon - 105.0, wgLat - 35.0);
var radLat = wgLat / 180.0 * PI;
var magic = Math.sin(radLat);
magic = 1 - OFFSET * magic * magic;
var sqrtMagic = Math.sqrt(magic);
dLat = (dLat * 180.0) / ((AXIS * (1 - OFFSET)) / (magic * sqrtMagic) * PI);
dLon = (dLon * 180.0) / (AXIS / sqrtMagic * Math.cos(radLat) * PI);
return [dLon, dLat]
}
function outOfChina(lon, lat) {
if (lon < 72.004 || lon > 137.8347) {
return true
}
if (lat < 0.8293 || lat > 55.8271) {
return true
}
return false
}
function transformLat(x, y) {
var ret = -100.0 + 2.0 * x + 3.0 * y + 0.2 * y * y + 0.1 * x * y + 0.2 * Math.sqrt(Math.abs(x));
ret += (20.0 * Math.sin(6.0 * x * PI) + 20.0 * Math.sin(2.0 * x * PI)) * 2.0 / 3.0;
ret += (20.0 * Math.sin(y * PI) + 40.0 * Math.sin(y / 3.0 * PI)) * 2.0 / 3.0;
ret += (160.0 * Math.sin(y / 12.0 * PI) + 320 * Math.sin(y * PI / 30.0)) * 2.0 / 3.0;
return ret
}
function transformLon(x, y) {
var ret = 300.0 + x + 2.0 * y + 0.1 * x * x + 0.1 * x * y + 0.1 * Math.sqrt(Math.abs(x));
ret += (20.0 * Math.sin(6.0 * x * PI) + 20.0 * Math.sin(2.0 * x * PI)) * 2.0 / 3.0;
ret += (20.0 * Math.sin(x * PI) + 40.0 * Math.sin(x / 3.0 * PI)) * 2.0 / 3.0;
ret += (150.0 * Math.sin(x / 12.0 * PI) + 300.0 * Math.sin(x / 30.0 * PI)) * 2.0 / 3.0;
return ret
}
gcj02.toWGS84 = forEachPoint(function(input, output, offset) {
var lng = input[offset];
var lat = input[offset + 1];
if (!outOfChina(lng, lat)) {
var deltaD = delta(lng, lat);
lng = lng - deltaD[0];
lat = lat - deltaD[1]
}
output[offset] = lng;
output[offset + 1] = lat
});
gcj02.fromWGS84 = forEachPoint(function(input, output, offset) {
var lng = input[offset];
var lat = input[offset + 1];
if (!outOfChina(lng, lat)) {
var deltaD = delta(lng, lat);
lng = lng + deltaD[0];
lat = lat + deltaD[1]
}
output[offset] = lng;
output[offset + 1] = lat
});
var bd09 = {};
var PI = Math.PI;
var X_PI = PI * 3000 / 180;
function toGCJ02(input, output, offset) {
var x = input[offset] - 0.0065;
var y = input[offset + 1] - 0.006;
var z = Math.sqrt(x * x + y * y) - 0.00002 * Math.sin(y * X_PI);
var theta = Math.atan2(y, x) - 0.000003 * Math.cos(x * X_PI);
output[offset] = z * Math.cos(theta);
output[offset + 1] = z * Math.sin(theta);
return output
}
function fromGCJ02(input, output, offset) {
var x = input[offset];
var y = input[offset + 1];
var z = Math.sqrt(x * x + y * y) + 0.00002 * Math.sin(y * X_PI);
var theta = Math.atan2(y, x) + 0.000003 * Math.cos(x * X_PI);
output[offset] = z * Math.cos(theta) + 0.0065;
output[offset + 1] = z * Math.sin(theta) + 0.006;
return output
}
bd09.toWGS84 = function(input, opt_output, opt_dimension) {
var output = forEachPoint(toGCJ02)(input, opt_output, opt_dimension);
return gcj02.toWGS84(output, output, opt_dimension)
};
bd09.fromWGS84 = function(input, opt_output, opt_dimension) {
var output = gcj02.fromWGS84(input, opt_output, opt_dimension);
return forEachPoint(fromGCJ02)(output, output, opt_dimension)
};
var projzh = {};
projzh.smerc2bmerc = function(input, opt_output, opt_dimension) {
var output = sphericalMercator.inverse(input, opt_output, opt_dimension);
output = bd09.fromWGS84(output, output, opt_dimension);
return baiduMercator.forward(output, output, opt_dimension)
};
projzh.bmerc2smerc = function(input, opt_output, opt_dimension) {
var output = baiduMercator.inverse(input, opt_output, opt_dimension);
output = bd09.toWGS84(output, output, opt_dimension);
return sphericalMercator.forward(output, output, opt_dimension)
};
projzh.bmerc2ll = function(input, opt_output, opt_dimension) {
var output = baiduMercator.inverse(input, opt_output, opt_dimension);
return bd09.toWGS84(output, output, opt_dimension)
};
projzh.ll2bmerc = function(input, opt_output, opt_dimension) {
var output = bd09.fromWGS84(input, opt_output, opt_dimension);
return baiduMercator.forward(output, output, opt_dimension)
};
projzh.ll2smerc = sphericalMercator.forward;
projzh.smerc2ll = sphericalMercator.inverse;
var extent = [72.004, 0.8293, 137.8347, 55.8271];
var baiduMercatorProj = new ol.proj.Projection({
code: 'baidu',
extent: ol.extent.applyTransform(extent, projzh.ll2bmerc),
units: 'm'
});
ol.proj.addProjection(baiduMercatorProj);
console.log(baiduMercatorProj);
ol.proj.addCoordinateTransforms('EPSG:4326', baiduMercatorProj, projzh.ll2bmerc, projzh.bmerc2ll);
ol.proj.addCoordinateTransforms('EPSG:3857', baiduMercatorProj, projzh.smerc2bmerc, projzh.bmerc2smerc);
var bmercResolutions = new Array(19);
for (var i = 0; i < 19; i++) {
bmercResolutions[i] = Math.pow(2, 18 - i)
}
var layer = new ol.layer.Tile({
title: "baidu",
source: new ol.source.XYZ({
projection: 'baidu',
maxZoom: 18,
tileUrlFunction: function(tileCoord) {
var x = tileCoord[1];
var y = tileCoord[2];
var z = tileCoord[0];
return "https://mapor1.bdimg.com/tile/?qt=tile&x=" + x + "&y=" + y + "&z=" + z + "&styles=pl&udt=20171206&scaler=2"
},
tileGrid: new ol.tilegrid.TileGrid({
resolutions: bmercResolutions,
origin: [0, 0],
extent: ol.extent.applyTransform(extent, projzh.ll2bmerc),
tileSize: [256, 256]
})
})
});
2.GCJ02
GCJ-02是由中国国家测绘局（G表示Guojia国家，C表示Cehui测绘，J表示Ju局）制订的地理信息系统的坐标系统。它是一种对经纬度数据的加密算法，即加入随机的偏差。国内出版的各种地图系统（包括电子形式），必须至少采用GCJ-02对地理位置进行首次加密。
在处理这类投影坐标定义时，要了解其主要为地图投影的一种非线性保密处理技术。网上有一类小地理范围处理的一个技术手段，详细参照：wgtochina_lb
/**
* 这是一个比较粗暴的方法，假设gcj为线性加偏，并对其偏移值直接进行处理
* origin: [-20037508.342789244-534.9468834158033, 20037508.342789244 + 338.0657671787776]
*/
var proj_3857 = new ol.proj.get("EPSG:3857");
var proj_3857Extent = proj_3857.getExtent();
var resolutions3857 = [156543.03392804097, 78271.51696402048, 39135.75848201024, 19567.87924100512, 9783.93962050256, 4891.96981025128, 2445.98490512564, 1222.99245256282, 611.49622628141, 305.748113140705, 152.8740565703525, 76.43702828517625, 38.21851414258813, 19.109257071294063, 9.554628535647032, 4.777314267823516, 2.388657133911758, 1.194328566955879, 0.5971642834779395];
var tileGrid = new ol.tilegrid.TileGrid({
resolutions: resolutions3857,
tileSize: [256, 256],
extent: proj_3857Extent
origin: [ -20037508.342789244-534.9468834158033, 20037508.342789244 + 338.0657671787776 ]
});
还有一个方法方法就是要基于上面提到的方法进行范围内的纠偏定义，其实再BD09的示例代码里已经可以看到其应用，那么在这里就是需要再参照BD09声明的方式再对GCJ02进行投影定义以及转换定义，这里详细的代码就暂时先不贴出来了，让大家也尝试研究一下。
3.EPSG:4326
该坐标定义主要就是我们比较常见的地理经纬度坐标的定义了，这里坐标的表示单位为degree，对应我们在WGS84的常见的坐标表示。
4.EPSG:3857
该坐标其实与4326相对应，其主要表示我们地理经纬度坐标在平面投影处理下的内容，这里的坐标的表示单位为m，我们也常称其为大地格网坐标。
5.自定义坐标（结合proj4）
这里主要结合了第三方的扩展内容proj4和EPSG的相关标准定义，通过这两块内容的定义，在openlayers中定义用户所需的坐标内容，对数据进行准确的信息展示。
这里提供一个简单的例子:
// 1.定义图纸坐标内容,详见EPSG标准
proj4.defs("EPSG:4548","+proj=tmerc +lat_0=0 +lon_0=117 +k=1 +x_0=500000 +y_0=0 +ellps=GRS80 +units=m +no_defs");
// 2.使用转换方法，打印结果
console.log(proj4("EPSG:4548", "EPSG:4326", [595940.042, 2716202.735]))