3D three.js Create the ground surface of a 3D building - three.js

Question

Following my post last week three.js How to programatically produce a plane from dataset I come back to the community to solve a problem of definition of surface occupied on the ground by a 3D building.
The solution proposed in comments in this post works for this building but is not universal.
To make it universal I chose the following method: when the walls are built I create their clone in another group (see this previous post for walls creation)
// prepare the clones
var clones = new THREE.Group();
scene.add(clones);
var num=0;
// drawing the real walls
var wallGeometry = new THREE.PlaneGeometry(size,(hstair*batims[i][1]));
val = 0xFFFFFF;
opa = 0.5;
if(deltaX > deltaY){val = 0x000000; opa = 0.05;} // shaded wall
var wallMaterial = new THREE.MeshBasicMaterial({color:val,transparent:true, opacity:opa, side:THREE.DoubleSide});
var walls = new THREE.Mesh(wallGeometry, wallMaterial);
walls.position.set((startleft+endleft)/2,(hstair*batims[i][1])/2,(startop+endtop)/2);
walls.rotation.y = -rads;
scene.add(walls);
// add the pseudo-walls to scene
var cloneGeometry=new THREE.PlaneGeometry(long,3);
var cloneMaterial=new THREE.MeshBasicMaterial({color:0xff0000,transparent:true,opacity:0.5,side:THREE.DoubleSide});
var clone=new THREE.Mesh(pseudomursGeometry,pseudomursMaterial);
clone.position.set((startleft+endleft)/2,3,(startop+endtop)/2);
clone.rotation.y=-rads;
clones.add(clone);
num++;
The idea is now to rotate this pseudo-building so that the longest wall is vertical, which allows me to determine the exact floor area occupied with its boundingBox:
var angle=turn=0;
for(i=0; i<dists.length; i++) { // dists is the array of wall lengths
if(dists[i]==longs[0]){ // longs is the reordered lengths array
angle=angles[i][1]; // angle of the longest wall
}
}
// we can now rotate the whole group to put the longest wall vertical
if(angle>0){
turn = angle*-1+(Math.PI/2);
}
else {
turn = angle+(Math.PI/2);
}
clones.rotation.y=turn;
It works perfectly as long as the building has a right angle, whatever its shape: triangle, rectangle, bevel, right angle polygons,
var boundingBox = new THREE.Box3().setFromObject(clones);
var thisarea = boundingBox.getSize();
// area size gives the expected result
console.log('AREA SIZE = '+thisarea.x+' '+thisarea.y+' '+thisarea.z);
...but not when there are no more right angles, for example a trapezoid
The reason is that we rotate the group, and not the cloned walls. I can access and rotate each wall by
for(n=0;n<num;n++){
thisangle = clones.children[n].rotation.y;
clones.children[n].rotation.y = turn-thisangle;
}
But the result is wrong for the others pseudo-walls:
So the question is: how to turn each red pseudo-wall so that the longest one is vertical and the others remain correctly positioned in relation to it? In this way, any building with any shape can be reproduced in 3D with its internal equipment. Any idea on how to achieve this result?

Answer 1

A weird & ugly but well-working solution:
// 1. determines which is the longest side
for(i=0; i<dists.length; i++) {
if(dists[i]==longs[0]){
longest=i;
break; // avoid 2 values if rectangle
}
}
// 2. the group is rotated until the longest side has an angle in degrees
// close to 0 or 180
var letsturn = setInterval(function() {
clones.rotation.y += 0.01;
var group_rotation = THREE.Math.radToDeg(clones.rotation.y); // degrees
var stop = Math.round(angles[longest][0] - group_rotation);
// 3. stop when longest wall is vertical
if( (stop>=179 && stop<=181) || (stop>=-1 && stop<=1) ) {
clearInterval(letsturn);
createPlane() // we can now use boundingBox in reliability
}
}, 1);
et voilà.