that's how I did it:

line 86-88 is probably interesting:

• please note that the x and z pos of the cam is derived with cos and sin, so the cam is rotating around the center (in 3D the floor is a plane in x and z direction; y direction would be above it).
• The y-pos (height) is just a value (depending on mouseY) and not to do with sin or cos

1. //
2. /* camera demonstration:  use mouse / mousewheel / Cursor   */
3. // ============================================================
4. // scene center :
5. int scene_XValue = 250; // nach rechts
6. int scene_YValue = 330; // nach unten
7. int scene_ZValue = -150; // nach hinten
8. // the boxes: 
9. int HoeheEinesBox = 20;
10. int TiefeEinesBox = 22;
11. int BreiteEinesBox = 50;
12. // camera
13. float camHeight = 0;    // height above the Scene
14. float Radius = 250.0;   // radius for camera
15. // =============================================================
16. void setup() {
17.   size(620, 640, OPENGL);
18.   background(153);
19. }
20. void draw() {
21.   background(153);
22.   CheckCameraMouse ();
23.   paintScene();
24. }
25. // ================================================
26. void mouseWheel(MouseEvent event) {
27.   float e = event.getAmount();
28.   // println(e);
29.   Radius+=e*2;
30.   // Wenn zu klein, dann bei -2 einfrieren
31.   if (Radius<-2) {
32.     Radius=-2;
33.   }
34. }
35. void keyPressed() {
36.   // Keyboard
37.   if (key == CODED) {
38.     // Spezialtasten wie z.B. Cursortasten:
39.     if (keyCode == UP ) {
40.       camHeight++;
41.     }
42.     else if (keyCode == DOWN ) {
43.       camHeight--;
44.     }
45.     else if (keyCode == RIGHT ) {
46.       Radius++;
47.     }
48.     else if (keyCode == LEFT ) {
49.       Radius--;
50.       // Wenn zu klein, dann bei -2 einfrieren
51.       if (Radius<-2) {
52.         Radius=-2;
53.       }
54.     }    
55.     else {
56.       //
57.     }
58.   }
59.   else {  
60.     // not key == CODED
61.     // normale Tasten wie 0 oder 1
62.     if (key == '0') {
63.     }   
64.     else if (key == '1') {
65.     }       
66.     else if (key == '2') {
67.     }       
68.     else if (key == '3') {
69.     }       
70.     else {
71.       // do nothing
72.     }
73.   }
74. }
75. // ----------------------------------------------------
76. void CheckCameraMouse () {
77.   // Mouse
78.   //
79.   float angle = map(mouseX, 0, width, 360, 0);
80.   print ("Mouse-pos-X: "+mouseX);
81.   println (" -> angle: " + angle + ".");
82.   //
83.   camHeight = map(mouseY, 0, height, height+400, 0);
84.   //
85.   PVector camPos = new PVector();
86.   camPos.x = Radius*sin(radians(angle)) + scene_XValue;
87.   camPos.y = camHeight;
88.   camPos.z = Radius*cos(radians(angle)) + scene_ZValue;
89.   //
90.   camera (
91.   camPos.x, camPos.y, camPos.z,
92.   scene_XValue, scene_YValue, scene_ZValue,
93.   0.0, 1.0, 0.0
94.     );
95. }
96. // =================================================
97. void paintScene () {
98.   // paint Scene
99.   // 
100.   pushMatrix();
101.   int localHeight = 220;
102.   fill(190, 3, 3);
103.   translate(scene_XValue-0, scene_YValue+(localHeight / 2), scene_ZValue-0);
104.   rotateY(0.0);
105.   box(11, localHeight, 11); // x, y, z
106.   popMatrix();
107.   //
108.   // ein Box: nach hinten an der Zentralstange (Eintrag -19)
109.   pushMatrix();
110.   fill(190, 103, 103);
111.   translate(scene_XValue, scene_YValue+(HoeheEinesBox/2), scene_ZValue-19);
112.   rotateY(0.0);
113.   box(BreiteEinesBox, HoeheEinesBox, TiefeEinesBox); // x, y, z
114.   popMatrix();
115.   //
116.   // ein Box: nach vorn an der Zentralstange (Eintrag+19)
117.   pushMatrix();
118.   fill(190, 3, 92);
119.   translate(scene_XValue+(0), scene_YValue+(HoeheEinesBox/2), scene_ZValue+19);
120.   rotateY(0.0);
121.   box(BreiteEinesBox, HoeheEinesBox, TiefeEinesBox); // x, y, z
122.   popMatrix();
123.   //
124.   // ein Box: nach links(?) an der Zentralstange (Eintrag -19)
125.   pushMatrix();
126.   fill(190, 3, 243);
127.   translate(scene_XValue-19, scene_YValue+(HoeheEinesBox+20), scene_ZValue+19-TiefeEinesBox);
128.   rotateY(0.0);
129.   box(TiefeEinesBox, HoeheEinesBox, BreiteEinesBox); // x, y, z
130.   popMatrix();
131.   //
132.   // ein Box: nach rechts an der Zentralstange (Eintrag +19)
133.   pushMatrix();
134.   fill(190, 3, 243);
135.   translate(scene_XValue+19, scene_YValue+(HoeheEinesBox+20), scene_ZValue+19-TiefeEinesBox);
136.   rotateY(0.0);
137.   box(TiefeEinesBox, HoeheEinesBox, BreiteEinesBox); // x, y, z
138.   popMatrix();
139. }
140. // ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++

Greetings, Chrisir

If you need an answer, please send me a personal message since this forum doesn't notify.

Hello Chrisir,

Thx for your reply and your code that I knew, because I fint him on Open Precessing, and I work around for my project 3D camera.
But for the Yaxis, you don't turn around the object, you just go UP and DOWN.

I make a little work to understand the problem and imagine a solution, but nothing happen..I continue the work. Maybe it's a complex algorithm to syncronize the two direction?

I draw a rought to understand the problem, in green that's ok, in red the problem I think. When the sphere witness horizontale is on the front, in the same time the witness sphere verticale are on the back.
https://www.dropbox.com/s/g5aac9u5nscwwfi/rotation3D.jpg

I make a sketch too

1. void setup()
   {
     size(600,600, P3D) ;
     colorMode (HSB, 360,100,100) ;
   }
   
   void draw()
   {
     background(0);
     int distance = 350 ;
     camera(-distance, -distance +200, distance,      width/2, height/2, 0.0,      0.0, 1.0, 0.0);
    
     float size = 300 ;
    
     //red ellipse and  horizontal
       noFill() ;
     strokeWeight(5) ;
     stroke(10,100,100) ;
     PVector p_h = new PVector (width /2, height /2, 0 ) ;
     PVector s_h = new PVector (size, size ) ;
     PVector o_h = new PVector (90, 0, 0 ) ;
     ellipseP3D(p_h, s_h, o_h) ;
     //sphere witness horizontal
     pushMatrix() ;
     translate(AxisRotationPos(mouseX, size /2).x + width /2, 0 + height/2, AxisRotationPos(mouseX, size /2).z) ;
     fill(10,100,100) ; noStroke() ;
     sphere( 30 ) ;
     popMatrix() ;
    
     //white ellipse and vertical
     noFill() ;
     strokeWeight(5) ;
     stroke(20,0,100) ;
     PVector p_v = new PVector (width /2, height /2, 0 ) ;
     PVector s_v = new PVector (size, size ) ;
     PVector o_v = new PVector (0, 90, 0 ) ;
     ellipseP3D(p_v, s_v, o_v) ;
     //sphere witness vertical
     pushMatrix() ;
    // translate(AxisRotationPos(mouseX, size /2).x + width /2, 0 + height/2, AxisRotationPos(mouseX, size /2).z) ;
     translate(0 + width/2, AxisRotationPos(mouseY, size /2).y + width /2, AxisRotationPos(mouseY, size /2).z) ;
     fill(20,0,100) ; noStroke() ;
     sphere( 30 ) ;
     popMatrix() ;
   }
   
   
   
   float cyclusMouse ;
   
   PVector AxisRotationPos(float XY, float distanceToFocus)
   {
     PVector pos = new PVector (0,0,0) ;
    
     cyclusMouse = map(XY, 0, width, 0, TAU) ;
    
     PVector marge = new PVector((width -distanceToFocus *2.0) *.5,(height -distanceToFocus *2.0) *.5) ;
    
     float dataPosXY =  cos(cyclusMouse) *distanceToFocus ;
     float dataPosZ =  sin(cyclusMouse) *distanceToFocus ;
   
     pos = new PVector ( dataPosXY, dataPosXY, dataPosZ ) ;
   
                                  
     return pos ;
   }
2. 
   
3. void ellipseP3D(PVector pos, PVector size, PVector orientation )
   {
     //degree to radian
     float oX = map(orientation.x, 0, 360, 0, TAU ) ;
     float oY = map(orientation.y, 0, 360, 0, TAU ) ;
     float oZ = map(orientation.z, 0, 360, 0, TAU ) ;
    
     pushMatrix() ;
   
     translate (pos.x, pos.y, pos.z) ;
     rotateX(oX) ;
     rotateY(oY) ;
     rotateZ(oZ) ;
     ellipse( 0,0,size.x,size.y) ;
     popMatrix() ;
    
   }
   

I don't know
pretty hard
sorry



Greetings, Chrisir

If you need an answer, please send me a personal message since this forum doesn't notify.