Your comments

Put this in your component .MouseDown Event:

Dim o as Object = helixViewport.FindNearestVisual(e.GetPosition(helixViewport))

Yes, its possible.

If you work with a complex material, you need to create a MaterialGroup and Add all materials that will make your final material.

To apply the material in your model, you need to do this (

TryCast(mObj.Content, GeometryModel3D).Material = MaterialGroup

TryCast(mObj.Content, GeometryModel3D).BackMaterial = MaterialGroup

If you don't need back, just does not use them.

Example Basic Material with Image:

Dim b As New ImageBrush(TryCast(myImage, BitmapImage))

b.TileMode = 1
b.Viewport = New Rect(0, 0, b.TileMode, b.TileMode)
b.Opacity = 1
vMat = New DiffuseMaterial(b)
TryCast(vMat, DiffuseMaterial).Color = Colors.White

The properties Normals, TextureCoord and Positions are private in Helix DLL, but you can change the code and rebuild, or you can create your own class in your code, copying the code from helix.

The helix works with meshs, so, after you importer the .obj, you have a model. So, you don't work no more with the obj file. You can edit and after export again to another .obj.

Other thing thats important remember: If the obj does not have the normals vector, you have to generate them. When you open the .obj in notepad, you can see if haves normals or not.

A mesh is basically defined for positions, triangleIndices and textureCoord. But you can define the vectors normals too, to build a completed mesh. You can define de normals to each position or to each face, thats depends how do you want your model.

I will explain how works MeshBuilder Class:

1) Positions - Collection of vertices

2) TriangleIndices - Collection of indices from de list of positions. Ex: 1 3 2 means that will be build a triangle with the position 1, 3 and 2 from the list of positions, in this order. (The order has influence to decide if the triangle is in back-side or front-side)

3) TextureCoord - Collection of texture coord. The texture coord works with a point (2D - UV coord)

4) Normals - Collection of vectors normals. The vectors normals has big influence in your mesh. I recommend you to study this, like texture coordinates too.

This is the basic to programer 3D.

To zoom Extents:

CameraHelper.ZoomExtents(helix.Camera, helix.Viewport, 1000)

To change Camera:

cameraPerspective.LookDirection = New Vector3D(0, -10, 0)

cameraPerspective.UpDirection = New Vector3D(0, 0, 1)
cameraPerspective.Position = New Point3D(0, 10, 0)
cameraPerspective.FieldOfView = 45
You have to open the directory Examples, then open Wpf and click with right button and select Set as StartUP Project to run the examples. There's no problem this incompatible.
I started put shadows in my test software. Still have problems but I think that will work fine when I finish. I used this tutorial to start but I did a lot of things different. If someone is trying to make shadows or knows something more, lets go write here to learn more. =)

You can use this:

'All borders are a global variable because have the same Material
Dim border As New LinesVisual3D

Public Sub addRectangles()
addRectangleWithBorder(New Point3D(0, 0, 0), 10, 5)
End Sub

Sub addRectangleWithBorder(ByVal position As Point3D, ByVal width As Double, ByVal Lenght As Double)
Dim rectangle As New RectangleVisual3D

rectangle.Length = Lenght
rectangle.Width = width
rectangle.Origin = New Point3D(0, 0, 0)
rectangle.Material = Materials.Red
rectangle.BackMaterial = Materials.Red

Dim p1, p2, p3, p4 As Point3D

p1 = New Point3D(Lenght / 2, width / 2, 0)
p2 = New Point3D(Lenght / 2, -width / 2, 0)
p3 = New Point3D(-Lenght / 2, -width / 2, 0)
p4 = New Point3D(-Lenght / 2, width / 2, 0)

With border
.Thickness = 2




.Color = Colors.Black
End With

End Sub
Yes, this is a problem. You can use a material group to put differents materials in your model, but is not easy to work. You can join just similar models, and this models dont need to be together. If you have a yellow tube in one point and you have other yellow tube in other point, you can join them. In my project, I work in this mode to a fastest result.
You are using PNG image? Because the helix is not good with png transparency