I am big fan for race game. Now I try to build a 3d race game by myself.

I know a little about scene graph principle. But I just do not know how to design the track data? And how to organize these data in OpenGL?

Any ideas? Thanks.

Typically the process is that the track surface is modeled and textured in a 3d modeling package and saved to a common 3d file format. The 3d file format is then processed and the data is loaded into your game. The whole loading the 3d model data aspect is where layers above OpenGL can come in handy. The Open Asset Import Library should be able to help you though: http://assimp.sourceforge.net/

Other elements of the track can also be modeled such as tires and billboards. In some games a 3d level editor is used/created for the purpose of placing the 3d assets in a level. One example is Leadwerks http://www.leadwerks.com/werkspace/page/editor?showbanner=0

In this case you would have a "level" file that would control the position, orientation, and scale of various 3d models as well as other level properties.

I worked on a race game a long time ago. The track and scenary was modelled in 3ds Max and exported as a custom mesh format. Then also in 3ds Max we created the Race lines and overtaking lines which are used by the AI cars.

These were just invisible objects that were spaced along the length of the track that contained information such as the optimal speed that an AI car should be at that particular node. We exported them seperatly using a max script and then they wee read into the engine and used by the AI.

There are some open source racing games about. Look at http://www.speed-dreams.org/

All of the ones I have looked at have two sets of data.

The track is defined as a bunch of meshes so you can view frustrum cull as many as possible

For the physics you usually have a seperate file. The most common format I have come across defines the track as left , right turns ans straight.

So you would have something like

typedef struct Left
{
       float angle;   // number of degrees the turn passes through
       float length;  // length of the arc
       float bank;    // bank angle
       float pitch;    // height change
};

You use a track editor to match the course to the 3D mesh

Actually I had a quick look

Speed dreams seems to use a bicubic patch for each track segment. They store 16 edge points for each track segment and interpolate between the points for the physics system.