I wish to display the Fresnel zone in the chart in which I am hoping to rotate an ellipse by an arbitrary angle. I have given the starting and ending x and y coordinates and I want the ellipse to be rotated not at the center but at the starting point. I have taken help from the below link still I am unable to get a proper ellipse rotated with an angle. Any help would be highly appreciated. Also, the x coordinates need to be formatted to bring the ellipse together. But I am unable to manage that too.
Drawing (Fresnel) ellipse and major axis
<html lang="en">
<head>
<meta charset="UTF-8" />
<meta http-equiv="X-UA-Compatible" content="IE=edge" />
<meta name="viewport" content="width=device-width, initial-scale=1.0" />
<title>Document</title>
<script src="https://cdn.jsdelivr.net/npm/chart.js"></script>
<style>
.chart-container {
width: 600px;
}
</style>
</head>
<body>
<div class="chart-container">
<canvas id="myChart"></canvas>
</div>
<script>
var step = (2 * Math.PI) / 30;
console.log("step", step);
f = 217.25; // frequency
x1 = 0;
x2 = 15;
y2 = 250;
y1 = 130;
fr = f * Math.pow(10, 6); // frequency in Hz
c = 2.997925 * Math.pow(10, 8); // speed of light
lambda = c / fr;
xarr = [];
yarr = [];
a = (1 / 2) * Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2)); // radius of major axis
r = Math.sqrt((lambda * a) / 2); // radius of the minor axis
w = Math.atan2(y2 - y1, x2 - x1);
console.log(w);
for (i = 0; i <= 2 * Math.PI; i += step) {
xval = a * Math.cos(i);
yval = r * Math.sin(i);
xnew = (x1 + x2) / 2 + xval * Math.cos(w) - yval * Math.sin(w);
ynew = (y1 + y2) / 2 + xval * Math.sin(w) + yval * Math.cos(w);
xarr.push(xnew);
yarr.push(ynew);
}
console.log(xarr);
const data = {
labels: xarr,
datasets: [
{
data: yarr,
borderColor: "rgba(0,0,0,1)",
},
],
};
const config = {
type: "line",
data: data,
options: {
scales: {
x: {
ticks: {
maxTicksLimit: 5,
beginAtZero: true,
},
},
y: {
beginAtZero: true,
maxTicksLimit: 5,
grid: {
display: true,
},
},
},
},
};
const mychart = new Chart(document.getElementById("myChart"), config);
</script>
</body>
</html>````
You need to make your x axis a linear scale for your use case. By default it is a category axis, which means it just takes your labels aarray as labels. If you make the scale linear it will map the data to the correct point in the axis:
options: {
scales: {
x: {
type: 'linear'
}
}
}
Live example:
var step = (2 * Math.PI) / 30;
f = 217.25; // frequency
x1 = 0;
x2 = 15;
y2 = 250;
y1 = 130;
fr = f * Math.pow(10, 6); // frequency in Hz
c = 2.997925 * Math.pow(10, 8); // speed of light
lambda = c / fr;
xarr = [];
yarr = [];
a = (1 / 2) * Math.sqrt(Math.pow(x2 - x1, 2) + Math.pow(y2 - y1, 2)); // radius of major axis
r = Math.sqrt((lambda * a) / 2); // radius of the minor axis
w = Math.atan2(y2 - y1, x2 - x1);
for (i = 0; i <= 2 * Math.PI; i += step) {
xval = a * Math.cos(i);
yval = r * Math.sin(i);
xnew = ((x1 + x2) / 2 + xval * Math.cos(w) - yval * Math.sin(w)) + 2.335; // Just add the max amount that it goes into negative so it shifts the elipse into a positive x values only
ynew = (y1 + y2) / 2 + xval * Math.sin(w) + yval * Math.cos(w);
xarr.push(xnew);
yarr.push(ynew);
}
var options = {
type: 'line',
data: {
labels: xarr,
datasets: [{
label: '# of Votes',
data: yarr,
borderWidth: 1
}]
},
options: {
scales: {
x: {
type: 'linear'
}
}
}
}
var ctx = document.getElementById('chartJSContainer').getContext('2d');
new Chart(ctx, options);<body>
<canvas id="chartJSContainer" width="600" height="400"></canvas>
<script src="https://cdnjs.cloudflare.com/ajax/libs/Chart.js/3.8.0/chart.js"></script>
</body>