yjdp-web/public/lib/GeoGlobeSDK/GeoLevel.js

GeoGlobe.INCHES_PER_UNIT["m"] = 1/0.0254;//1/0.025399998;

//获取层级比例尺分母对应的级别
//var lvl_tdt = getLevelFormScale(2.958293554545656E8); //1

function getRealLevel(relativeLvl,scale, units, dpi){
	var lvl = getLevelFormScale(scale, units, dpi);
	return parseInt(relativeLvl) == lvl ? 0 : lvl;
}

//获得级别 scale第一个级别比例尺 units单位
function getLevelFormScale(scale, units, dpi){
	var units = units ? units : "degrees";
	var dpi = dpi ? dpi : 96;
	var resolution = getResolutionFromScale_DPI(scale, units, dpi);
	var lvl = getLevelFormResolution(resolution, units);
	return lvl;
}

function getResolutionFromScale_DPI(scale, units, dpi) {
    var resolution;
    if (scale) {
        if (units == null) {
            units = "degrees";
        }
        var normScale = GeoGlobe.Util.normalizeScale(scale);
        resolution = 1 / (normScale * GeoGlobe.INCHES_PER_UNIT[units] * dpi);
    }
    return resolution;
}

function getLevelFormResolution(resolution, units){
    if (!resolution) {
        return 0;
    }
	var zoom, i, diff;
	var minDiff = Number.POSITIVE_INFINITY;
	var resolutions = getResolutions(units);
	for (i = 0, len = resolutions.length; i < len; i++) {
		//判断当前分辨率与金字塔中分辨率最接近的
        diff = Math.abs(resolutions[i] - resolution);
        if (diff > minDiff) {
            break;
        }
        minDiff = diff;
	}
	zoom = Math.max(0, i - 1);//0和(i - 1)中取大数。
	return zoom ;
}

function getResolutions(units){
	var resolutions = new Array();
	for (var i = 0; i <= 20; i++) {
		resolutions.push(getResolutionForLevel(i, units));
	}
	return resolutions;
}

function getResolutionForLevel(level, units){
	//var topTileWidth = Math.abs(this.topTileToX - this.topTileFromX);//360
	var units = units ? units : "degrees";
	var topTileWidth = 360;//周长360度
	if(units === "m"){
		topTileWidth = 40075016.6855784;//周长40075016.6855784米=20037508.3427892*2 
	}
	var tileSize = 256;//256
	var maxResolution = (topTileWidth / 256);
	return maxResolution / Math.pow(2, level);		
}