Sims 3:0x015A1849

Header

Start with the RCOL Header: Sims 3:RCOL

Then the GEOM chunk:

long     'GEOM'
long     Version              // 5
long     TailOffset
long     TailSectionSize   // (0x14, 0x44 observed)
long     EmbeddedID     //(0, 0x548394B9 observed)
if(EmbeddedID!=0) {
   long ChunkSize
   byte[ChunkSize]       // starts with 'MTNF'
   }
long   0                      //unknown purpose
long   0                      // unknown purpose
long   NumVerts
long   FCount                            // was named Version, but is number of vertex elements
block  VertexFormat[FCount]      // long, long, byte; documented below 9 bytes/vertex-element-count
struct VertexData[NumVerts]     // follows vertex format block, documented below
block  FaceFmt                         // long ItemCount, byte BytesPerFacepoint
long   NumFacePoints                // means faces*3
word [NumFacePoints][3]         // standard face index (three unsigned words per face) for 2-byte FaceFmt

----------
Tail:
long  flags
long  count1
long  bonehasharray[count1]  // 32-bit hash of used bone names.
long  numtgi
block references[numtgi]  // each is a TGI[sub]64[/sub], a 16-byte quantity, so size is 16*numtgi
                                    // references are to DDS textures and BONE file

VertexFormat

For each vertex count:

long   DataType
long   SubType
byte   BytesPerElement

For DataType:
1  == Position (3 float == 12 bytes)
2  == Normal  (3 float == 12 bytes)
3  == UV       (2 float == 8 bytes)
4  == Bone Assignment (long == 4 bytes)
5  == Weights (4 float == 16 bytes)
6  == Tangent Normal (3 float == 12 bytes)
7  == TagVal (4 packed bytes) -- colour channel data
10 == VertexID (long == 4 bytes)

For SubType
1 == floats
2 == bytes
4 == long

You calculate the offset of each element from the sum of the previous BytesPerElement

Reading Vertex Data Blocks

For each vertex, you need to loop through the VertexFormat as defined, and read the information in order.

The order can be completely arbitary, and varied in size.

Here is some example code in c# to do so:

            for (int i = 0; i < numVerts; i++)
            {

                for (int j = 0; j < vertexFormats.Count; j++)
                {
                    float x = 0;
                    float y = 0;
                    float z = 0;

                    vertexFormat vf = (vertexFormat)vertexFormats[j];
                    switch (vf.dataType)
                    {
                        case 1:
                            x = reader.ReadSingle();
                            z = reader.ReadSingle();
                            y = reader.ReadSingle();
                            sb.AppendLine("  XYZ: " + x.ToString() + " " + y.ToString() + " " + z.ToString() );
                            break;
                        case 2:
                            x = reader.ReadSingle();
                            z = reader.ReadSingle();
                            y = reader.ReadSingle();
                            sb.AppendLine("  Normal: " + x.ToString() + " " + y.ToString() + " " + z.ToString() );
                            break;
                        case 3:
                            float u = reader.ReadSingle();
                            float v = reader.ReadSingle();
                            sb.AppendLine("  UV: " + u.ToString() + " " + v.ToString() );
                            break;
                        case 4:
                            sb.AppendLine("  Bone: " + reader.ReadUInt32().ToString() );
                            break;
                        case 5:
                            float w1 = reader.ReadSingle();
                            float w2 = reader.ReadSingle();
                            float w3 = reader.ReadSingle();
                            float w4 = reader.ReadSingle();
                            sb.AppendLine("  Weights: " + w1.ToString() + " " + w2.ToString() + " " + w3.ToString() + " " + w4.ToString() );
                            break;
                        case 6:
                            x = reader.ReadSingle();
                            z = reader.ReadSingle();
                            y = reader.ReadSingle();
                            sb.AppendLine("  Tangent Normal: " + x.ToString() + " " + y.ToString() + " " + z.ToString() );
                            break;
                        case 7:
                            // Note, not splitting this up yet just reading an int
                            sb.AppendLine("  TagVal: " + reader.ReadUInt32().ToString() );
                            break;
                        case 10:
                            sb.AppendLine("  VertexID: " + reader.ReadUInt32().ToString() );
                            break;

                    }

                }
            }

Note that basically we just look through the VertexFormat, and read the data in order. There is no fixed "vertex format" version, it's all controlled via the vertexformat data.