I wanted to build a section box inside forge viewer. I have the minx, maxX, minY, maxY through area marking. Also I have minZ and maxZ through level selection (levels[i].elevation – globalOffset.Z).
I want a similar functionality like the default Add Box button in Section Analysis but I want to add the min max co-ordinates 
Can you please help me with this?
Here you go ~ Please refer to the following code snippet to calculate cut plane parameters for the viewer:
const minPt = new THREE.Vector3( -82.73119354248047, -115.42709350585938, -31.42848777770996 ); //!<<< put your point here
const maxPt = new THREE.Vector3( -0.0000020212402347397074, 0, 0 ); //!<<< put your point here
const normals = [
new THREE.Vector3(1, 0, 0),
new THREE.Vector3(0, 1, 0),
new THREE.Vector3(0, 0, 1),
new THREE.Vector3(-1, 0, 0),
new THREE.Vector3(0, -1, 0),
new THREE.Vector3(0, 0, -1)
];
const bbox = new THREE.Box3( minPt, maxPt );
const cutPlanes = [];
for( let i = 0; i < normals.length; i++ ) {
const plane = new THREE.Plane( normals[i], -1 * maxPt.dot( normals[i] ) );
// offset plane with negative normal to form an octant
if( i > 2 ) {
const ptMax = plane.orthoPoint( bbox.max );
const ptMin = plane.orthoPoint( bbox.min );
const size = new THREE.Vector3().subVectors( ptMax, ptMin );
plane.constant -= size.length();
}
const n = new THREE.Vector4( plane.normal.x, plane.normal.y, plane.normal.z, plane.constant );
cutPlanes.push( n );
}
viewer.setCutPlanes( cutPlanes );
