Obj2Tiles - Converts OBJ file to 3D Tiles format

Obj2Tiles is a fully fledged tool to convert OBJ files to 3D Tiles format. It creates multiple LODs, splits the mesh and repacks the textures.

Installation

You can download precompiled binaries for Windows, Linux and macOS from https://github.com/OpenDroneMap/Obj2Tiles/releases.

Command line parameters

  Input (pos. 0)         Required. Input OBJ file.
  Output (pos. 1)        Required. Output folder.
  
  -s, --stage            (Default: Tiling) Stage to stop at (Decimation, Splitting, Tiling)
  
  -l, --lods             (Default: 3) How many levels of details

  -d, --divisions        (Default: 2) How many tiles divisions
  -z, --zsplit           (Default: false) Splits along z-axis too
  -k, --keeptextures     (Default: false) Keeps original textures
  
  --lat                  Latitude of the mesh
  --lon                  Longitude of the mesh
  --alt                  (Default: 0) Altitude of the mesh (meters)
  -e, --error            (Default: 100), baseError value for root node
  --scale                (Default: 1), scale for data if using units other than meters ( 1200.0/3937.0 for survey ft)  
  
  --y-up-to-z-up         (Default: false) Converts Y-up to Z-up
  
  --use-system-temp      (Default: false) Uses the system temp folder
  --keep-intermediate    (Default: false) Keeps the intermediate files (do not cleanup)
      
  --help                 Display this help screen.
  --version              Display version information.

The pipeline is composed of the following steps:

Decimation

The source obj is decimated using the Fast Quadric Mesh Simplification algorithm (by Mattias Edlund). The algorithm was ported from .NET Framework 3.5 to .NET Core 6.0. The original repo is here.

You can specify how many LODs (levels of detail) you want to generate using the --lods parameter. The decimation levels are generated using this formula:

quality[i] = 1 - ((i + 1) / lods)

For example: with 5 LODs the program will use the following quality levels: 80%, 60%, 40%, 20%. If you specify 1 LOD, the decimation will be skipped.

Splitting

For every decimated mesh, the program splits it recursively along x, y and z axis (optional using the --zsplit flag). Every split is a new mesh with repacked textures (to save space), the bin pack algorithm is by Jukka Jylänki. If you want to preserve the original textures, use the --keeptextures flag (not recommended)

You can control how many times the split is performed by using the --divisions flag. The model will be split into divisions^2 meshes (or divisions^3 if --zsplit is used).

3D Tiles conversion

Each split mesh is converted to B3DM format using ObjConvert. Then the tileset.json is generated using the resulting files. You can specify the --lat and --lon and --alt parameters to set the location of the model. See the Remarks section to find out how to rotate the model.

Running

Obj2Tiles is built using .NET Core 8.0. Releases are available on GitHub for a multitude of platforms (win / linux / mac). You can download the latest release or compile it yourself using the following commands:

git clone https://github.com/OpenDroneMap/Obj2Tiles.git
cd Obj2Tiles
dotnet build -c Release

Examples

You can download the test obj file here. The Brighton Beach textured model generated using OpenDroneMap.

Basic usage (using defaults)

It runs all the pipeline stages and generates the tileset.json file in the output folder.

Obj2Tiles model.obj ./output

Decimation

Stop the pipeline at the decimation stage and generate 8 LODs

Obj2Tiles --stage Decimation --lods 8 model.obj -o ./output

Splitting

Stop the pipeline at the splitting stage and generate 3 divisions per axis

Obj2Tiles --stage Splitting --divisions 3 model.obj ./output

Full pipeline

Run all the pipeline stages and generate the tileset.json file in the output folder.

Obj2Tiles --lods 8 --divisions 3 --lat 40.689434025350025 --lon -74.0444987716782 --alt 120 model.obj ./output

Rotating the model

After generating tileset.json, you can edit the file and change the 4x4 Transform matrix to account for translation, rotation and scaling. This is the matrix structure:

The tiling stage uses this matrix to place the model in the requested geo location:

But you can add scaling:

Or rotation around any of the 3 axes:

By combining these matrices, you can rotate, scale and translate the model.

You can find more details about this topic on BrainVoyager

Remarks

All the pipeline stages are multi threaded to speed up the process. You can stop the pipeline at any stage by providing the --stage flag. If you need to keep the intermediate files, use the --keep-intermediate flag. You can use the --use-system-temp flag to use the system temp folder instead of the output folder.