android - 在圆圈中画东西线？

Question

我目前正在构建一个小型指南针应用程序，并使用简单的圆方程绘制了南北线：x= a+r Cos(t) and y= b+ r Sin(t) where t=heading or direction in degree(angle ）。更多信息在 Wiki

到目前为止，我已经设法获得了南北线。这是我的工作

    //canvas.drawLine(startX, startY, stopX, stopY, paint)

    //Drawing North
        canvas.drawLine(cxCompass, cyCompass, 
                (float)(cxCompass + radiusCompass * Math.sin((double)(-direction) * 3.14/180)), 
                (float)(cyCompass - radiusCompass * Math.cos((double)(-direction) * 3.14/180)), 
                paint);

    //Drawing South
        canvas.drawLine(cxCompass, cyCompass, 
                (float)(cxCompass - radiusCompass * Math.sin((double)(-direction) * 3.14/180)), 
                (float)(cyCompass + radiusCompass * Math.cos((double)(-direction) * 3.14/180)), 
                paint);

我的问题：我不知道我们如何获得东西线？

CxCompass, CyCompass：圆心坐标

Answer 1

通过添加 90 度修复了该问题。我很乐意分享

            //Drawing west
        canvas.drawLine(cxCompass, cyCompass, 
                (float)(cxCompass + radiusCompass * Math.sin((double)(-direction-90) * 3.14/180)), 
                (float)(cyCompass - radiusCompass * Math.cos((double)(-direction-90) * 3.14/180)), 
                paint);

        //Drawing east
        canvas.drawLine(cxCompass, cyCompass, 
                (float)(cxCompass - radiusCompass * Math.sin((double)(-direction-90) * 3.14/180)), 
                (float)(cyCompass + radiusCompass * Math.cos((double)(-direction-90) * 3.14/180)), 
                paint);