Scripting : Align along normal

[guillaume laforge <guillaume.laforge.3d(at)gmail.com>]

Hi list :-)

 

I'm learning XSIMath and I can't find how to align an object along the POLYGON normal ? My script seems to work but it doesn't align perfectly along polygon normal :-/. As I'm new to those things I'm wondering if I miss something in the 3d math logic or if in XSI the polygon normal is a special case (compared to normals on points ).

 

Here is my script :

 

//AlignAlongNormal.js
//Select one polygon, run the script and pick an object.
//-----------------------------------------------------

//Get the selected polygon
var polySel = Selection.item(0).subcomponent.componentcollection;
var oPolygonFace = polySel(0);
//Get the Polygon Normal
var oPolygonNode = oPolygonFace.Nodes(0);
var >
//Get the Polygon points
1 );
//-----------------------------------------
//Find the Position.
var oPos = XSIMath.CreateVector3();
for ( var i = 0 ; i < oNborsPoints.count ; i++ )
{
oPos.x = oPos.x+oNborsPoints(i).Position.x;
oPos.y = oPos.y+oNborsPoints(i).Position.y;
oPos.z = oPos.z +oNborsPoints(i).Position.z;
}
oPos.x = oPos.x/oNborsPoints.count;
oPos.y = oPos.y/oNborsPoints.count;
oPos.z = oPos.z /oNborsPoints.count; 

//-------------Align the picked object------------------
//Pick session
var oPicked = PickObject ("Please pick an object") ;
var buttonChoice = oPicked.Value( "ButtonPressed" ) ;
var MyObj = oPicked.item(2);

//Rotation
MyObj.kinematics.global.transform = RotationFromPoly(oNormal) ;

//Position
MyObj.Kinematics.Global.Parameters("posx").value = oPos.x;
MyObj.Kinematics.Global.Parameters("posy").value = oPos.y;
MyObj.Kinematics.Global.Parameters("posz").value = oPos.z;

//**********From Ray-T Function**********
function RotationFromPoly(polyNormal)
{
var upVec = XSIMath.CreateVector3();
upVec.set(0, 1, 0);
var axis = XSIMath.CreateVector3();
axis.cross(upVec, polyNormal);
var angle = Math.acos(upVec.dot(polyNormal));
var rot = XSIMath.CreateRotation();
rot.SetFromAxisAngle(axis, angle);
var transfo = XSIMath.CreateTransform();
transfo.SetRotation(rot);

return transfo;
}

Any advice from experienced user is welcome !

Cheers,

Guillaume Laforge
CG artist | Jr td :)