How to calculate the SVG Path for an arc (of a cir

Question

Given a circle centered at (200,200), radius 25, how do I draw an arc from 270 degree to 135 degree and one that goes from 270 to 45 degree?

0 degree means it is right on the x-axis (the right side) (meaning it is 3 o' clock position) 270 degree means it is 12 o'clock position, and 90 means it is 6 o'clock position

More generally, what is a path for an arc for part of a circle with

x, y, r, d1, d2, direction

meaning

center (x,y), radius r, degree_start, degree_end, direction

Answer 1

I wanted to comment on @Ahtenus answer, specifically on Ray Hulha comment saying the codepen does not show any arc, but my reputation is not high enough.

The reason for this codepen not working is that its html is faulty with a stroke-width of zero.

I fixed it and added a second example here : http://codepen.io/AnotherLinuxUser/pen/QEJmkN.

The html :

<svg>
    <path id="theSvgArc"/>
    <path id="theSvgArc2"/>
</svg>

The relevant CSS :

svg {
    width  : 500px;
    height : 500px;
}

path {
    stroke-width : 5;
    stroke       : lime;
    fill         : #151515;
}

The javascript :

document.getElementById("theSvgArc").setAttribute("d", describeArc(150, 150, 100, 0, 180));
document.getElementById("theSvgArc2").setAttribute("d", describeArc(300, 150, 100, 45, 190));

Answer 2

I slightly modified the answer of opsb and made in support fill for the circle sector. http://codepen.io/anon/pen/AkoGx

JS

function polarToCartesian(centerX, centerY, radius, angleInDegrees) {
  var angleInRadians = (angleInDegrees-90) * Math.PI / 180.0;

  return {
    x: centerX + (radius * Math.cos(angleInRadians)),
    y: centerY + (radius * Math.sin(angleInRadians))
  };
}

function describeArc(x, y, radius, startAngle, endAngle){

    var start = polarToCartesian(x, y, radius, endAngle);
    var end = polarToCartesian(x, y, radius, startAngle);

    var arcSweep = endAngle - startAngle <= 180 ? "0" : "1";

    var d = [
        "M", start.x, start.y, 
        "A", radius, radius, 0, arcSweep, 0, end.x, end.y,
        "L", x,y,
        "L", start.x, start.y
    ].join(" ");

    return d;       
}

document.getElementById("arc1").setAttribute("d", describeArc(200, 400, 100, 0, 220));

HTML

<svg>
  <path id="arc1" fill="orange" stroke="#446688" stroke-width="0" />
</svg>

Answer 3

@opsb's answers is neat, but the center point is not accurate, moreover, as @Jithin noted, if the angle is 360, then nothing is drawn at all.

@Jithin fixed the 360 issue, but if you selected less than 360 degree, then you'll get a line closing the arc loop, which is not required.

I fixed that, and added some animation in the code below:

function myArc(cx, cy, radius, max){       
       var circle = document.getElementById("arc");
        var e = circle.getAttribute("d");
        var d = " M "+ (cx + radius) + " " + cy;
        var angle=0;
        window.timer = window.setInterval(
        function() {
            var radians= angle * (Math.PI / 180);  // convert degree to radians
            var x = cx + Math.cos(radians) * radius;  
            var y = cy + Math.sin(radians) * radius;
           
            d += " L "+x + " " + y;
            circle.setAttribute("d", d)
            if(angle==max)window.clearInterval(window.timer);
            angle++;
        }
      ,5)
 }     

  myArc(110, 110, 100, 360);
    

<svg xmlns="http://www.w3.org/2000/svg" style="width:220; height:220;"> 
    <path d="" id="arc" fill="none" stroke="red" stroke-width="2" />
</svg>

Answer 4

you can use JSFiddle code i made for answer above:

https://jsfiddle.net/tyw6nfee/

all you need to do is change last line console.log code and give it your own parameter:

  console.log(describeArc(255,255,220,30,180));
  console.log(describeArc(CenterX,CenterY,Radius,startAngle,EndAngle))

Answer 5

A slight modification to @opsb's answer. We cant draw a full circle with this method. ie If we give (0, 360) it will not draw anything at all. So a slight modification made to fix this. It could be useful to display scores that sometimes reach 100%.

function polarToCartesian(centerX, centerY, radius, angleInDegrees) {
  var angleInRadians = (angleInDegrees-90) * Math.PI / 180.0;

  return {
    x: centerX + (radius * Math.cos(angleInRadians)),
    y: centerY + (radius * Math.sin(angleInRadians))
  };
}

function describeArc(x, y, radius, startAngle, endAngle){

    var endAngleOriginal = endAngle;
    if(endAngleOriginal - startAngle === 360){
        endAngle = 359;
    }

    var start = polarToCartesian(x, y, radius, endAngle);
    var end = polarToCartesian(x, y, radius, startAngle);

    var arcSweep = endAngle - startAngle <= 180 ? "0" : "1";

    if(endAngleOriginal - startAngle === 360){
        var d = [
              "M", start.x, start.y, 
              "A", radius, radius, 0, arcSweep, 0, end.x, end.y, "z"
        ].join(" ");
    }
    else{
      var d = [
          "M", start.x, start.y, 
          "A", radius, radius, 0, arcSweep, 0, end.x, end.y
      ].join(" ");
    }

    return d;       
}

document.getElementById("arc1").setAttribute("d", describeArc(120, 120, 100, 0, 359));

Answer 6

An image and some Python

Just to clarify better and offer another solution. Arc [A] command use the current position as a starting point so you have to use Moveto [M] command first.

Then the parameters of Arc are the following:

rx, ry, x-axis-rotation, large-arc-flag, sweep-flag, xf, yf

If we define for example the following svg file:

<svg width="5cm" height="5cm" viewBox="0 0 500 500"

xmlns="http://www.w3.org/2000/svg" version="1.1">

The following code will give you this result:

<g stroke="none" fill="lime">
<path d="
M 250 250
A 100 100 0 0 0 450 250
Z"/> 
</g>

You will set the starting point with M the ending point with the parameters xf and yf of A.

We are looking for circles so we set rx equal to ry doing so basically now it will try to find all the circle of radius rx that intersect the starting and end point.

import numpy as np

def write_svgarc(xcenter,ycenter,r,startangle,endangle,output='arc.svg'):
    if startangle > endangle: 
        raise ValueError("startangle must be smaller than endangle")

    if endangle - startangle < 360:
        large_arc_flag = 0
        radiansconversion = np.pi/180.
        xstartpoint = xcenter + r*np.cos(startangle*radiansconversion)
        ystartpoint = ycenter - r*np.sin(startangle*radiansconversion)
        xendpoint = xcenter + r*np.cos(endangle*radiansconversion)
        yendpoint = ycenter - r*np.sin(endangle*radiansconversion)
        #If we want to plot angles larger than 180 degrees we need this
        if endangle - startangle > 180: large_arc_flag = 1
        with open(output,'a') as f:
            f.write(r"""<path d=" """)
            f.write("M %s %s" %(xstartpoint,ystartpoint))
            f.write("A %s %s 0 %s 0 %s %s" 
                    %(r,r,large_arc_flag,xendpoint,yendpoint))
            f.write("L %s %s" %(xcenter,ycenter))
            f.write(r"""Z"/>""" )

    else:
        with open(output,'a') as f:
            f.write(r"""<circle cx="%s" cy="%s" r="%s"/>"""
                    %(xcenter,ycenter,r))

You can have a more detailed explanation in this post that I wrote.