Ken Silverman's Voxlap5 VXL format
06/28/2004: Notes first written (not tested though)
08/02/2004: Tested code for 1st time.. found&fixed major bug!

Here's some C pseudo-code:
//----------------------------------------------------------------------------
typedef struct { double x, y, z; } dpoint3d;
dpoint3d ipos, istr, ihei, ifor;

	//Called at least once for every voxel of the board
	//issolid: 0:air, 1:solid
void setgeom (long x, long y, long z, long issolid) { /*your code here*/ }

	//Called only for surface voxels
	//A surface voxel is any solid voxel with at least 1 air voxel
	//  on one of its 6 sides. All solid voxels at z=0 are automatically
	//  surface voxels, but this is not true for x=0, x=1023, y=0, y=1023,
	//  z=255 (I believe)
	//argb: 32-bit color, high byte is used for shading scale (can be ignored)
void setcol (long x, long y, long z, long argb) { /*printf("%d %d %d: %08x\n",x,y,z,argb);*/ }

long loadvxl (char *filnam)
{
	FILE *fil;
	long i, x, y, z;
	unsigned char *v, *vbuf;

	fil = fopen(filnam,"rb"); if (!fil) return(-1);
	fread(&i,4,1,fil); if (i != 0x09072000) return(-1);
	fread(&i,4,1,fil); if (i != 1024) return(-1);
	fread(&i,4,1,fil); if (i != 1024) return(-1);
	fread(&ipos,24,1,fil); //camera position
	fread(&istr,24,1,fil); //unit right vector
	fread(&ihei,24,1,fil); //unit down vector
	fread(&ifor,24,1,fil); //unit forward vector

		//Allocate huge buffer and load rest of file into it...
	i = filelength(_fileno(fil))-ftell(fil);
	vbuf = (unsigned char *)malloc(i); if (!vbuf) { fclose(fil); return(-1); }
	fread(vbuf,i,1,fil);
	fclose(fil);

		//Set entire board to solid
	for(z=0;z<256;z++)
		for(y=0;y<1024;y++)
			for(x=0;x<1024;x++)
				setgeom(x,y,z,1);

	v = vbuf;
	for(y=0;y<1024;y++)
		for(x=0;x<1024;x++)
		{
			z = 0;
			while (1)
			{
				for(i=z;i<v[1];i++) setgeom(x,y,i,0);
				for(z=v[1];z<=v[2];z++) setcol(x,y,z,*(long *)&v[(z-v[1]+1)<<2]);
				if (!v[0]) break; z = v[2]-v[1]-v[0]+2; v += v[0]*4;
				for(z+=v[3];z<v[3];z++) setcol(x,y,z,*(long *)&v[(z-v[3])<<2]);
			}
			v += ((((long)v[2])-((long)v[1])+2)<<2);
		}

	free(vbuf);
}
//----------------------------------------------------------------------------
You need to write the body of setgeom() and setcol(). Obviously, you can
replace them and write directly to your own data buffers. I just wrote it this
way for simplicity. I recommend you store solid/air geometry data separately
from the colors. For a 1024x1024x256 size, using a 32MB bit array is
reasonable. For colors, probably the easiest thing is to use hashing since
the surface voxels are sparse.

-Ken S.