Transform face to a known plane

[Garry K]

I have a face that can be on any plane. I need to transform it so that it is on a specific plane. Does anyone know how to do this.

In most cases the specific plane will be flat on the ground.

[jolran]

The "specific plane" ? I assume you mean the modeling plane where the face is located to start with ?

It says in the API

Geom::Transformation.new(origin, zaxis)

Don't remember if it was this one I used..
Try: origin, a Point on the plane and zaxis should then be the plane normal.

Edit: Be aware though that it's not really a reliable method since only providing 1 vector and not a frame. Sketchup does some thinking and comparing to decide what is supposed to become X and Y axis. So if rotation is important you have to do some extra work..

Oh and you have to reset translation to ORIGIN before moving it to the face. I guess you could use a vector instead. Anyhew...
If you have a plane and not a face. The plane is an Array[3] with Point and normal.

ents = Sketchup.active_model.entities
face = Sketchup.active_model.selection.grep(Sketchup;;Face)[0]
gp = Sketchup.active_model.selection.grep(Sketchup;;Group)[0]
	
normal = face.normal
c = face.bounds.center
tr1 = Geom;;Transformation.new(c,normal)
#reset to ORIGIN
gpc = gp.bounds.center
tr = Geom;;Transformation.new([-gpc[0],-gpc[1],-gpc[2]], Z_AXIS)

gp.transform!(tr1*tr)

[Garry K]

The face can be rotated on both x and y axis.

The key part is that rourke has centroid code but it only works on a face that is parallel to the ground.

What I want to do is transform the points of the face to ground plane, calculate the centroid and then transform the centroid back so it lays on the original face.

[sdmitch]

@garry k said:

What I want to do is transform the points of the face to ground plane, calculate the centroid and then transform the centroid back so it lays on the original face.

Not sure where I found this code but it will calculate the centriod of xyz pts.

def calc_centroid(f)
 tx=0.0;ty=0.0;tz=0.0;
 p=f.outer_loop.vertices.collect{|v|v.position}
 p.each{|v| tx+=v.x;ty+=v.y;tz+=v.z}
 ax=tx/p.length;ay=ty/p.length;az=tz/p.length
 c=Geom;;Point3d.new(ax,ay,az);#ent.add_cpoint(c)
 area = 0.0;cx = 0.0;cy = 0.0;cz = 0.0;
 for i in 0...p.length
  areat = (p[i].distance(p[i-1])*(c.distance_to_line([p[i],p[i].vector_to(p[i-1])])))/2.0
  area = area + areat;
  cx = cx + areat * ( p[i].x + p[i-1].x + c.x ) / 3.0;
  cy = cy + areat * ( p[i].y + p[i-1].y + c.y ) / 3.0;
  cz = cz + areat * ( p[i].z + p[i-1].z + c.z ) / 3.0;
 end
 cx = cx / area;cy = cy / area;cz = cz / area;
 Geom;;Point3d.new(cx,cy,cz)
end

[Garry K]

Thanks sdmitch

This indeed produces a centroid on a face.

I also need to transform the face to ground level. The reason is I will need to do some panel optimization. So I need the shapes on ground level.

[jolran]

Ok missed the the key part in the first post....

It might be difficult to find a general solution if you want the correct X or Y rotation flat at the ground from a reversed face transformation ? Don't know if anyone found a simple solution to that unless digging in at entity level and comparing angles.
For a simple rectangle face it might be solvable, but a complex polygon how do you tell which edge or vertice to use for alignment ? It's easier to do with parametric Surface and derivatives

An alternative might be to use Vector3d.axes, where you form your own axes with the face.normal as Z-axis and use those with your Formulas. Might remove the need to move the face to Origin. Same problem with alignment though but when creating a tempgroup for a faceclone ( you can't move the original )its Z-axis is not pointing in the face normal direction, so there is quite some work to make the boundingbox aligned so the face is flat on the ground when reversing transformations..

[CAUL]

@garry k said:

I have a face that can be on any plane. I need to transform it so that it is on a specific plane. Does anyone know how to do this.

In most cases the specific plane will be flat on the ground.

I think the code below works:

module AlignToNormal

  def self.get_alignment_matrix(face_normal, p, plane_normal)
    return Geom;;Transformation.new if (plane_normal.dot(face_normal)- 1).abs < 0.00000001   
    cv = face_normal.cross(plane_normal)
    a = face_normal.angle_between(plane_normal)
    return Geom;;Transformation.rotation(p, cv, a)
  end
  
  def self.get_centroid(f)
    c = Geom;;Point3d.new(0, 0, 0)
    f.outer_loop.vertices.map { |v| v.position }.each { |p| 
      c.x += p.x ; c.y += p.y; c.z += p.z
    }
    div = f.outer_loop.vertices.length
    c.x = c.x / div; c.y = c.y / div; c.z = c.z / div;
    return c
  end

  def self.main
    mod = Sketchup.active_model
    ent = mod.entities
    sel = mod.selection
    
    f = sel.grep(Sketchup;;Face)[0]
    centroid = get_centroid(f)
    m = get_alignment_matrix(f.normal, centroid, Geom;;Vector3d.new(1, 1, 1).normalize!)
    ent.transform_entities(m, f)
  end
  
  main
end

[jolran]

That's nice but..

@unknownuser said:

I also need to transform the face to ground level. The reason is I will need to do some panel optimization. So I need the shapes on ground level.

I gather this information as he actually DO want the face to the ground to do something with it there. Maybe I'm wrong this time as well.

Edit, sorry missed the part in the code where one can edit the plane. Your code seams to work for the purpose of getting the plane correct!

[CAUL]

@jolran said:

I gather this information as he actually DO want the face to the ground to do something with it there. Maybe I'm wrong this time as well.

You can concatenate transformations with multplication:

align = get_alignment_matrix(face_normal, centroid, plane_normal)
translate = Geom;;Transformation.translation(to_point - centroid)
align_and_translate = translate * align
ent.transform_entities(align_and_translate, f)

[Garry K]

Thanks guys - I've adjusted Caul's code and I can now get everything working the way I want.

[Garry K]

The plane is rotated from the ground plane on all axis.

[fredo6]

Usually, you achieve this with Geom::Transformation.axes.

In your case, assuming the face is at top level of the model:

tr_axe_inv = Geom;;Transformation.axes(face.vertices[0].position, *(face.normal.axes)).inverse

tr_axe_inv is the transformation to be used for the projection.

Fredo

[Garry K]

Thanks Fredo,

Seems like there is always something new to learn !!

[fredo6]

This projects the face on the XY plane, with vertex 0 at Origin.

If you wish to project to another plane, say with [pt2, normal2], use an additional direct Axe transformation.

Fredo

[CAUL]

@fredo6 said:

> tr_axe_inv = Geom;;Transformation.axes(face.vertices[0].position, *(face.normal.axes)).inverse
> 

Neat! Just saved fifteen lines of code in a script...