vtlib: Importing 3D Models

Currently Model Functionality

The method vtLoadModel uses OSG to import 3D geometry from a file, and returns it as a node which can be added to the scene, and optionally placed on the terrain.

The most commonly useful formats include the following, depending on which extensions DLLs have been built with the library:

• .3ds (3D Studio)
• .dae (Collada)
• .flt (Open Flight)
• .lwo (LightWave)
• .obj (Alias Wavefront)

These five formats have been tested and known to work reasonably well, within the limitations of each format.  OSG supports a long list of less-common formats as well.

Another option is to export directly to an OSG-specific format:

• osgexport, an open-source exporter from Blender.  It writes the .osg format.
• OSGExp, an open-source exporter from 3DS MAX.  It can write either the ASCII .osg format, or the compact .ive binary format.

If you are using Blender, see How to use Blender with OSG/VTP.

Working with loaded models

First, you will almost certainly want to add your model to the scene graph, by using addChild to add it to some existing node:

vtGroup *root = vtGetScene().GetRoot();
root->addChild(node);

If you are writing your code in a vtTerrain subclass method (your own terrain), you can alternately use vtTerrain::AddNode to add the node to the terrain's scene graph:

void MyTerrain::CreateCustomCulture()
{
    NodePtr node = vtLoadModel(...);
    AddNode(node);
}

To move/scale your model, you can attach it to a transform node:

vtTransform *trans = new vtTransform;
trans->addChild(node);

To control placement of your model on the terrain, you can use the vtTerrain methods provided:

void vtTerrain::PlantModel(vtTransform *model);
void vtTerrain::PlantModelAtPoint(vtTransform *model, const DPoint2 &pos);

The PlantModel method moves your object vertically such that it lies on the terrain surface, PlantModelAtPoint first places the object a specific earth coordinate before planting it down.

Long-term issues with the Art Path into vtlib

• It is of course a vital capability read geometry from popular 3D modeling programs, e.g. 3D Studio MAX.  The problem is that no good, standard 3D file format exists.  They all have limitations and drawbacks.

• Experimental native vtlib format: SOG (only partially developed)
  • Read and write of vtGeode to SOG is implemented
  • Would need to write a MAX plugin to output the new format.  The free library Flexporter should make this much easier.  Unfortunately Flexporter makes it difficult to control the order in which components are output - should be able to work around that.
  • A Blender plugin to export SOG would be even easier.

Blender

There is a 3D modeling package that is popular, and as Free as the VTP - Blender. 
Tested this possibility in August 2006: Blender to OSG.