0
216
ViewsThree js calculate sphere from polar coordinates
I am useing three.js an want to calculate a sphere. I am using two for loops one for theta and one for phi and then transforming the polar coordinates to Cartesian coordinates. For every calculated point I added a Point. The result is not a sphere.
This is the nested for loop:
const distance = 1000;
for (var i = 0; i < 360; i += 10) {
for (let j = 0; j < 360; j += 10) {
let theta = i * (Math.PI / 180);
let phi = j * (Math.PI / 180);
let x = Math.sin(theta) * Math.cos(phi) * distance;
let y = Math.sin(theta) * Math.sin(phi) * distance;
let z = distance * Math.sin(phi);
const lightSphere = new THREE.Mesh(sphereGeometry, sphereMaterial);
lightSphere.position.set(x, y, z);
scn.add(lightSphere);
}
}
And here is the full code, including the result: Link
1 answers
Answer question0
j must be in range [-90, 90] 9instead of [0, 260]. Notice that you are creating slices (360 °) from the South Pole to the North Pole (180 °).
You must compute the sin(theta) and the cos(theta) and multiply both with cos(phi):
let x = Math.sin(theta) * Math.cos(phi) * distance;
let y = Math.sin(theta) * Math.sin(phi) * distance;
let x = Math.cos(theta) * Math.cos(phi) * distance;
let y = Math.sin(theta) * Math.cos(phi) * distance;
Complete algorithm:
const distance = 1000;
for (var i = 0; i < 360; i += 10) {
for (let j = -90; j < 90; j += 10) {
let theta = i * (Math.PI / 180);
let phi = j * (Math.PI / 180);
let x = Math.cos(theta) * Math.cos(phi) * distance;
let y = Math.sin(theta) * Math.cos(phi) * distance;
let z = distance * Math.sin(phi);
const lightSphere = new THREE.Mesh(sphereGeometry, sphereMaterial);
lightSphere.position.set(x, y, z);
scn.add(lightSphere);
}
}
You create circles (slices) using Polar coordinate (distance, theta). The Cartesian coordinate can be get by:
xc = cos(theta) * distance
yc = sin(theta) * distance
Finally you do something similar for the sphere:
x = xc * cos(phi)
y = yc * cos(phi)
z = sin(phi) * distance