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Index › Programming Questions & Help › OpenGL and 3D Libraries › using Vec3D (or 3d directions in general)
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using Vec3D (or 3d directions in general) (Read 1202 times)
gabon
using Vec3D (or 3d directions in general)
Jul 10th, 2008, 3:34pm  
Hi guys, I'm trying to play with 3D vectors, I'm using toxi's ones but my problem is about 3d in general).

I've a motion defined by a Vec3D. I can easily draw the direction of it doing:
Code:

private void drawVec(Vec3D v, Point3D p, float radius)
{
float ax = getContextualAngle(v.x);
float ay = getContextualAngle(v.y);
float az = getContextualAngle(v.z);

float dx = radius * sin(ax);
float dy = radius * sin(ay);
float dz = radius * sin(az);

Point3D newP = new Point3D(p.x + dx, p.y + dy, p.z + dz);
drawLine(0x00FF00, p,newP);
}


where getContextualAngle is simply
Code:

private float getContextualAngle(float vecAngle)
{
// R90 is radians(90)
return map(vecAngle, -1, 1, -R90, R90);
}


I would like to define that circle perpendicular to the vector (each point is equally distant from the next point resulting from the vector).

As start I thought to try and drawing it, so one translated to a point rotating the camera I could simply drawing it, but my problem is of course finding out the rotations to apply. My problem I presume is also in understanding if I have to rotate only on two axis.

Any tips a part study geometry? Smiley


Thanks, chr
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JohnG
Re: using Vec3D (or 3d directions in general)
Reply #1 - Jul 10th, 2008, 3:57pm  
I really have no idea what your first piece of code is doing.. if I wanted to draw a line along the direction of motion, I'd just use:

Code:
void drawVec(Vec3D v, Point3D p)
{
  drawLine(0x00FF00,p,new Point3D(p.x+v.x,p.y+v.y,p.z+v.z));
}


As for drawing a circle perpendicular to this, I did something ages ago that requires working such things out:
http://www.hardcorepawn.com/Anenome/ If you look in the Tube class, there's code which draws a cylinder from point a to point b (in my code they're Vertexes not Point3Ds but I believe it should still be able to copy most of it directly.
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gabon
Re: using Vec3D (or 3d directions in general)
Reply #2 - Jul 10th, 2008, 4:03pm  
Hi John, well, you are absolutely right about the inutility of that code (how newbie I am!) :S

now I converted to:
Code:

drawLine(0x00FF00, p, new Point3D(p.x + v.x * radius, p.y + v.y * radius, p.z + v.z * radius));


I'll check your class, thanks a lot!

chr
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gabon
Re: using Vec3D (or 3d directions in general)
Reply #3 - Jul 10th, 2008, 6:09pm  
I adapted your code to my case, now to draw the perpendicular my method is:

Code:

private void drawVec(Vec3D v, Point3D p, float radius)
{
Point3D next = new Point3D(p.x + v.x * radius, p.y + v.y * radius, p.z + v.z * radius);
drawLine(0x00FF00, p, next);
// draw circle
int RESOLUTION = 20;
float RH = RESOLUTION * .5f;
float heading, pitch;

Point3D[] points = new Point3D[RESOLUTION];

    float len=sqrt((next.x-p.x)*(next.x-p.x)+(next.y-p.y)*(next.y-p.y)+(next.z-p.z)*(next.z-p.z));
    len/=2;
    Point3D mid = new Point3D((p.x + next.x) / 2,
				(p.y + next.y) / 2,
				((p.z + next.z) / 2));
		heading = atan2(v.z, v.x) * -1;
		pitch = atan2(v.y, sqrt((v.x * v.x) + (v.z * v.z)));
    
    float x, y, z;
    int i;
    for(i=0;i<RESOLUTION;i++)
    { 
      // rod is horizontal along X to start
    Point3D cp=new Point3D(-len,radius*cos(i*(PI/RH)),radius*sin(i*PI/RH));
    //pitch, then heading
    x = cp.x;
    y = cp.y;
    cp.x = x*cos(pitch)+y*cos(pitch+HALF_PI);
    cp.y=x*sin(pitch)+y*sin(pitch+HALF_PI);
    z = cp.z;
    x = cp.x;
    cp.z=z*cos(heading)+x*cos(heading+HALF_PI);
    cp.x=z*sin(heading)+x*sin(heading+HALF_PI);

      //move tube so that it goes from one end to the other.      
    cp.x+=mid.x;
    cp.y+=mid.y;
    cp.z+=mid.z;
    points[i] = cp;
    }
    // draw
    fill(255,0,0);
    beginShape();
    Point3D s;
    for(i=0;i<points.length;i++)
    {
      s = points[i];
      vertex(s.x,s.y,s.z);
    }
    endShape();
}


Thanks John, chr
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