obj to b3dm Use draco compression

[mylove10086]

Hello, I have completed the conversion of obj to gltf using the draco compression model. But when I converted obj to a 3dtiles b3dm file and used the draco compression model, there was no success. When loading 3dtiles in cesium, the browser prompted ‘Unsupported draco mesh geometry type.’
But I didn't find the documentation about draco compressed 3dtiles on the cesium official website.
I have a question
How do I use draco to compress 3dtiles?

[lilleyse]

@mylove10086 did you use https://github.com/CesiumGS/gltf-pipeline or some other tool to do the draco compression? Could you post the obj and gltf?

[mylove10086]

I refer to https://github.com/KhronosGroup/COLLADA2GLTF to complete the obj conversion gltf and b3dm. However, when using draco to compress b3dm tiles, there is an error when loading in cesium. The error in the browser is ‘Unsupported draco mesh geometry type.’ I do n’t know where the problem is now. I guess it's in gltf:
"extensionsRequired": [
     "KHR_draco_mesh_compression"
   ],
   "extensionsUsed": [
     "KHR_draco_mesh_compression"
   ]. do you have any good advice. Is there a reference to b3dm files done using draco compression?

[mylove10086]

This is part of the b3dm compressed by draco:
{
  "BATCH_LENGTH": 1
} {
  "batchId": [
    0
  ],
  "name": [
    "Plane"
  ],
  "maxPoint": [
    [
      6.4123969078063969,
      0.0,
      6.4123969078063969
    ]
  ],
  "minPoint": [
    [
      -6.4123969078063969,
      0.0,
      -6.4123969078063969
    ]
  ]
}
{
  "asset": {
    "version": "2.0",
    "copyright": "Mylove",
    "generator": "CObj2Gltf @ Mylove"
  },
  "scenes": [
    {
      "nodes": [
        0
      ]
    }
  ],
  "scene": 0,
  "nodes": [
    {
      "name": "Plane_node",
      "mesh": 0
    }
  ],
  "meshes": [
    {
      "name": "Plane_Mesh",
      "primitives": [
        {
          "name": "Plane_primitive",
          "extensions": {
            "KHR_draco_mesh_compression": {
              "bufferView": 0,
              "attributes": {
                "NORMAL": 1,
                "POSITION": 0
              }
            }
          },
          "attributes": {
            "NORMAL": 1,
            "POSITION": 2,
            "_BATCHID": 3
          },
          "indices": 0,
          "mode": 4,
          "material": 0
        }
      ]
    }
  ],
  "accessors": [
    {
      "name": "Plane_indices",
      "count": 6,
      "type": "SCALAR",
      "componentType": 5123,
      "max": [
        3
      ],
      "min": [
        0
      ]
    },
    {
      "name": "Plane_normal",
      "count": 4,
      "type": "VEC3",
      "componentType": 5126,
      "max": [
        0.0,
        1.0,
        0.0
      ],
      "min": [
        0.0,
        1.0,
        0.0
      ]
    },
    {
      "name": "Plane_position",
      "count": 4,
      "type": "VEC3",
      "componentType": 5126,
      "max": [
        6.4123969078063969,
        0.0,
        6.4123969078063969
      ],
      "min": [
        -6.4123969078063969,
        0.0,
        -6.4123969078063969
      ]
    },
    {
      "name": "Plane_batchId",
      "byteOffset": 0,
      "bufferView": 1,
      "count": 4,
      "type": "SCALAR",
      "componentType": 5123,
      "max": [
        0
      ],
      "min": [
        0
      ]
    }
  ],
  "materials": [
    {
      "name": "None",
      "pbrMetallicRoughness": {
        "baseColorFactor": [
          0.800000011920929,
          0.800000011920929,
          0.800000011920929,
          1.0
        ],
        "metallicFactor": 0.0,
        "roughnessFactor": 1.0
      },
      "emissiveFactor": [
        0.0,
        0.0,
        0.0
      ],
      "alphaMode": "OPAQUE"
    }
  ],
  "bufferViews": [
    {
      "buffer": 0,
      "byteLength": 127,
      "byteOffset": 0
    },
    {
      "name": "Plane_batchId_bufferView",
      "buffer": 0,
      "byteLength": 8,
      "byteOffset": 0,
      "byteStride": 0,
      "target": 34962
    }
  ],
  "buffers": [
    {
      "byteLength": 135
    }
  ],
  "extensionsRequired": [
    "KHR_draco_mesh_compression"
  ],
  "extensionsUsed": [
    "KHR_draco_mesh_compression"
  ]
}

[lilleyse]

Here's an example .b3dm and .gltf: 0.zip

[lilleyse]

Does the glTF work before it is converted to a b3dm?

[mylove10086]

When you do not use draco to compress b3dm, it can load and display normally in the browser. Draco compressed gltf is also possible. But draco compressed b3dm cannot be displayed in the browser.

[mylove10086]

I have found the problem by looking at the model 0.b3dm file that you donated. When using draco to compress b3dm, there is no "_BATCHID" compression. Now I have a problem: when using draco to compress _BATCHID, the type of draco should be used:
class GeometryAttribute {
  public:
   // Supported attribute types.
   enum Type {
     INVALID = -1,
     // Named attributes start here. The difference between named and generic
     // attributes is that for named attributes we know their purpose and we
     // can apply some special methods when dealing with them (e.g. during
     // encoding).
     POSITION = 0,
     NORMAL,
     COLOR,
     TEX_COORD,
     // A special id used to mark attributes that are not assigned to any known
     // predefined use case. Such attributes are often used for a shader specific
     // data.
     GENERIC,
     // Total number of different attribute types.
     // Always keep behind all named attributes.
     NAMED_ATTRIBUTES_COUNT,
   };

[mylove10086]

thank you very much for your help. But the draco compressed b3dm model was still unsuccessful. This is my gltf and b3dm model using draco compression, but b3dm cannot be displayed in the browser. Can you find the reason for me.
Uploading 1.zip…

[mylove10086]

1.zip

This is the model I converted

[mylove10086]

谢谢，我已经成功了！
Thank you, I have succeeded!

[yulongyu]

你好 能指点下我怎么转3dtiles格式么