Processing 1.0 - Processing Discourse - Problems with spherical coordinates

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Index › Programming Questions & Help › OpenGL and 3D Libraries › Problems with spherical coordinates

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Problems with spherical coordinates (Read 995 times)

controller

Problems with spherical coordinates
Apr 15^th, 2006, 8:27pm

Hi!

I don't know why the following code doesn't draw a sphere consisting of a few smaller spheres.

I made comments in the code to further explain what's the problem.

Quote:

void setup() {
framerate(40);
size(300,300,P3D);
background(255);

c = new Circle();
c.p = 75;
}

Circle c;

void draw() {

translate(width/2,height/2,0);

// ********************* //
// Why do these lines not draw a Sphere consisting of
// a few smaller spheres?
for (float p = 0; p<TWO_PI; p += PI/10) {
c.phi = p;
for (float t = 0; t<TWO_PI; t += PI/10) {
c.theta = t;
c.display();
}
}

// if you uncomment the following lines and
// comment the above lines, the program does
// draw a sphere like I want it

/*c.theta += PI/10;

if (c.theta > TWO_PI) {
c.theta = 0;
c.phi += PI/10;
}

c.display();*/

}

class Circle {

float p,theta,phi;
float x,y,z;

Circle() {
p = 0;
theta = 0;
phi = 0;
x = 0;
y = 0;
z = 0;
}

void display() {

SphericalToCartesian();

noStroke();
fill(50);
translate(x,y,z);
sphere(3);
}

void SphericalToCartesian() {
z = p*sin(phi)*cos(theta);
x = p*sin(phi)*sin(theta);
y = p*cos(phi);
}
}

controller YaBB Newbies Offline Posts: 13	Re: Problems with spherical coordinates Reply #1 - Apr 15^th, 2006, 9:35pm Another problem is how to position the spheres steady-going. By now, for example on the top or bottom will be just as many spheres as in the middle, but the radius of the ring they form is much smaller. Anyone got an idea how to solve this problem?

Henrik

Re: Problems with spherical coordinates
Reply #2 - Apr 17^th, 2006, 3:05pm

Hey,
didnt really understand the problem of the first post, but your second problem i've also stumbled over; how to position the spheres 'steady going'.
What you need is some kind of geodesic form, like the icosahedron or anything similar, depending on you resolution. these are spheres where the points are equally spaced apart. I was not able to find a formula for this, so i used Blender to make one, and exported it as an .OBJ file and read it using the OBJLoader library.
Hope this helps

Henrik

controller YaBB Newbies Offline Posts: 13	Re: Problems with spherical coordinates Reply #3 - Apr 17^th, 2006, 3:18pm Hi, thanks for your answer. I know I didn't explain the first problem very good. When you copy the sourcecode into processing and start it, you'll know what the problem is.

st33d

Re: Problems with spherical coordinates
Reply #4 - Apr 17^th, 2006, 5:59pm

You weren't using popMatrix() and pushMatrix();

You intended to start from 0,0,0 and jump out to a point on the sphere. But because you didn't clear the translation from memory and put yourself back at 0,0,0 on the next iteration you proceeded onwards from the edge of the sphere to some ungodly co-ords.

The following code works, it looks quite pretty, well done.
Quote:

Circle c;
void setup() {
framerate(40);
size(300,300,P3D);
background(255);
c = new Circle();
c.p = 75;
}
void draw() {
translate(width/2,height/2,100);
for (float p = 0; p<TWO_PI; p += PI/10) {
c.phi = p;
for (float t = 0; t<TWO_PI; t += PI/10) {
c.theta = t;
c.display();
}
}
}

class Circle {
float p,theta,phi;
float x,y,z;
Circle() {
p = 0;
theta = 0;
phi = 0;
x = 0;
y = 0;
z = 0;
}
void display() {
SphericalToCartesian();
noStroke();
fill(50);
pushMatrix();
translate(x,y,z);
sphere(3);
popMatrix();
}
void SphericalToCartesian() {
z = p*sin(phi)*cos(theta);
x = p*sin(phi)*sin(theta);
y = p*cos(phi);
}
}

A cheap fix for the extra spheres at the polar caps would be to reduce the iterations. Another method might be to look at the source code for Processing's sphere() method. I tried looking myself on dev.processing.org and I've no idea where they keep the bloody thing. Good luck.

controller YaBB Newbies Offline Posts: 13	Re: Problems with spherical coordinates Reply #5 - Apr 17^th, 2006, 6:52pm thank you, that was what I was looking for. I also took a look at dev.processing.org, but I find it very confusing. Unfortunately there's no zipped source code available for processing.

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