计算成都市两地间车程在三环内外的分布（片段）

estimates.js.coffee

get_distance = ->
    
    map = new BMap.Map('allmap')
    map.centerAndZoom(new BMap.Point(104.072, 30.663), 13)
    
    old_ads = ... # 地点1的坐标
    new_ads = ... # 地点2的坐标
    
    old_point = new BMap.Point(old_ads[x],old_ads[y])
    new_point = new BMap.Point(new_ads[x],new_ads[y])
        
    get_ratio = (point1,point2) ->
        
        # 根据球面坐标获得平面坐
        get_mecator = (poi) ->
            map.getMapType().getProjection().lngLatToPoint(poi)
        
        # 判断点是否在三环内
        point_in_circle = (pot) ->
            res = (pot.x-dot.x)*(pot.x-dot.x) + (pot.y-dot.y)*(pot.y-dot.y) - r*r
            if res > 0
                false
            else
                true
        
        # 当两地跨域三环时，获取三环外车程比例
        get_cross_rat = (x, x2) ->
            x ||= x2
            if point_in_circle(pot1)
                rat = Math.abs(pot2.x - x) / Math.abs(pot1.x - pot2.x)
            else
                rat = Math.abs(pot1.x - x) / Math.abs(pot1.x - pot2.x)
            rat
        
        # 原点设置为 天府广场地铁站
        #   球面坐标 104.072486, 30.66348
        #   平面坐标(百度) 11585422.2, 3567130.97
        #   计算方式 dot = get_mecator(new BMap.Point(104.072486, 30.66348))
        # 半径设置为 9300
        r = 9300.0
        dot = x: 11585422.2, y: 3567130.97
        pot1 = get_mecator(point1)
        pot2 = get_mecator(point2)
        
        # 两点直线方程 y=kx+d
        k = (pot2.y - pot1.y) / (pot2.x - pot1.x)
        d = pot1.y - k * pot1.x
        
        # 直线与园切点方程 ax2+bx+c=0
        a = 1 + k * k
        b = 2 * (k * d - k * dot.y - dot.x)
        c = dot.x * dot.x + dot.y * dot.y + d * d - 2 * dot.y * d - r * r
        
        det = b * b - 4 * a * c
        if det < 0
            # console.log('无解')
            x1 = null
            x2 = null
        else
            x1 = (Math.sqrt(det) - b) / (2*a)
            x2 = (0 - Math.sqrt(det) - b) / (2*a)
            
            if (x1-pot1.x)*(x1-pot2.x) > 0
                # console.log('x1无用根')
                x1 = null
                
            if (x2-pot1.x)*(x2-pot2.x) > 0
                # console.log('x2无用根')
                x2 = null
        
        if x1? && x2?           # 两点都在三环外，内切三环
            rat = 1 - ( (x1 - x2) / Math.abs(pot1.x - pot2.x) )
        else if x1? || x2?             # 跨越三环
            rat = get_cross_rat(x1, x2)
        else                    # 都在三环内 或 都在三环外但不过三环
            rat = `point_in_circle(pot1) ? 0 : 1`
            
        # console.log('rat='+rat)
        rat
        
    rat = get_ratio(old_point,new_point)
    
    transit = new BMap.DrivingRoute(map, {
        onSearchComplete: (results) ->
            # console.log(results.getPlan(0))
            if transit.getStatus() != BMAP_STATUS_SUCCESS
                return
            distance = results.getPlan(0).getDistance(false) / 1000

            distance_out = Math.ceil( distance * rat )
            distance_in =  Math.round( distance * (1 - rat) )
            distances = [distance_in, distance_out]
            
            # save distances # distances便是结果
            
        });
    transit.search(old_point,new_point)