如何找到某一點的角度

Question

我使用start和endangle繪制了svg圈，如下所示，

document.getElementById("circle").setAttribute("d", describeArc(150, 150, 100, 180, 360));
            function getPathArc(center, start, end, radius) {
                        end = end - 0.0001;
                        var degree = end - start;
                        degree = degree < 0 ? (degree + 360) : degree;
                        var clockWise = (degree < 180) ? 0 : 1;
                        return getPiePath(center, degreeToLocation(start, radius, center), degreeToLocation(end, radius, center), radius, clockWise);
            }
            function getPiePath(center, start, end, radius, clockWise) {
                        return 'M ' + start.x + ' ' + start.y + ' A ' + radius + ' ' + radius + ' 0 ' + clockWise + ' 1 ' + end.x + ' ' + end.y;
            };          
            function degreeToLocation(degree, radius, center) {
                    var radian = (degree * Math.PI) / 180;
                    return { 
                        'x' : Math.cos(radian) * radius + center.x,
                        'y': Math.sin(radian) * radius + center.y
                    };
            }           
            function describeArc(x, y, radius, startAngle, endAngle){
                var endAngle = endAngle - startAngle;
                startAngle = startAngle <= 0 ? (360 + startAngle) % 360 : startAngle % 360;
                endAngle = endAngle < 0 ? (360 + endAngle + startAngle) % 360 : Math.abs(endAngle + startAngle) % 360;
                    var direction = getPathArc({'x': x, 'y': y}, startAngle, endAngle, radius);
                    var d = direction;
                    return d;       
            }

這是樣本https://jsfiddle.net/ndmsqmao/3/

我需要為指定點繪制該圓圈的一個刻度線。

比如讓我們考慮一下，

如果它的值從50到100開始意味着我需要繪制第66個值的一個刻度線..如何實現這個？

Answer 1

希望這可以幫助...

var minValue = 50, maxValue = 100, value = 66,
    minAngle = 180, maxAngle = 360, angle;

angle = minAngle + (value - minValue) / (maxValue - minValue) * (maxAngle - minAngle);

alert(angle);

Answer 2

我希望我理解你的問題......

var min = 50;
var max = 100;
var value = 66;

var angle = 180/(max-min)*(value-min)+180;

console.log (angle);