GeoMotionGPT

GeoMotionGPT is a motion-to-text model that converts human motion sequences into natural language descriptions.

Model Components

This model integrates two components:

1. Motion Tokenizer (DVQ-GSST)

• Architecture: Decoder-only Vector Quantizer with Gumbel-Softmax Straight-Through quantization
• Codebook Size: 512 tokens
• Input: 263-dimensional motion features (HumanML3D format)
• Temporal Downsampling: 8x (3 downsampling layers with stride 2)

2. Language Model (Fine-tuned GPT-2)

• Base Model: GPT-2 (124M parameters)
• Task: Motion-to-Text generation
• Training: Fine-tuned with orthogonality regularization (λ=0.01)
• Total Vocab: 50772 tokens (50257 text + 512 motion + 3 special)

Quick Start: Motion Tokenization

from transformers import AutoModelForCausalLM
import torch

# Load the model
model = AutoModelForCausalLM.from_pretrained(
    "zy22b/GeoMotionGPT", 
    trust_remote_code=True
)

# Access the motion tokenizer
motion_tokenizer = model.motion_tokenizer

# Example: Tokenize motion (batch, time, 263)
motion = torch.randn(1, 100, 263)  # Random motion features
with torch.no_grad():
    tokens = motion_tokenizer.encode(motion)  # -> (batch, time//8)
print(f"Motion tokens shape: {tokens.shape}")

# Example: Decode tokens back to motion
with torch.no_grad():
    reconstructed = motion_tokenizer.decode(tokens)  # -> (batch, time, 263)
print(f"Reconstructed shape: {reconstructed.shape}")

Usage with HumanML3D Data

import numpy as np
import torch
from transformers import AutoModelForCausalLM

# Load model
model = AutoModelForCausalLM.from_pretrained(
    "zy22b/GeoMotionGPT", 
    trust_remote_code=True
)
motion_tokenizer = model.motion_tokenizer

# Load HumanML3D motion file
motion = np.load("datasets/humanml3d/new_joint_vecs/000000.npy")  # (T, 263)

# Load normalization parameters
mean = np.load("datasets/humanml3d/Mean.npy")
std = np.load("datasets/humanml3d/Std.npy")

# Normalize
motion_norm = (motion - mean) / std

# Convert to tensor and add batch dimension
motion_tensor = torch.FloatTensor(motion_norm).unsqueeze(0)  # (1, T, 263)

# Tokenize
with torch.no_grad():
    tokens = motion_tokenizer.encode(motion_tensor)
    
print(f"Input shape: {motion_tensor.shape}")   # e.g., torch.Size([1, 116, 263])
print(f"Token shape: {tokens.shape}")          # e.g., torch.Size([1, 14])
print(f"Tokens: {tokens[0].tolist()}")         # e.g., [138, 104, 508, ...]

Full Motion-to-Text Generation

The following is a complete, self-contained script for motion-to-text generation.

Requirements:

pip install torch transformers numpy safetensors huggingface_hub

Complete Code:

"""
GeoMotionGPT: Complete Motion-to-Text Generation
Self-contained script - requires only: torch, transformers, numpy, safetensors
"""

import torch
import numpy as np
from transformers import AutoModelForCausalLM, AutoTokenizer, GPT2LMHeadModel, GPT2Config
from safetensors.torch import load_file


class GeoMotionGPTGenerator:
    """Complete Motion-to-Text Generator using HuggingFace models."""
    
    def __init__(self, device="cuda" if torch.cuda.is_available() else "cpu"):
        self.device = torch.device(device)
        self.text_vocab_size = 50257
        self.motion_codebook_size = 512
        
        # Load motion tokenizer from HuggingFace
        print("Loading motion tokenizer from HuggingFace...")
        hf_model = AutoModelForCausalLM.from_pretrained(
            "zy22b/GeoMotionGPT", 
            trust_remote_code=True
        )
        self.motion_tokenizer = hf_model.motion_tokenizer.to(self.device)
        self.motion_tokenizer.eval()
        
        # Load GPT2 tokenizer
        print("Loading GPT2 tokenizer...")
        self.tokenizer = AutoTokenizer.from_pretrained("gpt2")
        self.tokenizer.pad_token = self.tokenizer.eos_token
        
        # Add motion tokens to tokenizer
        motion_tokens = [f'<motion_id_{i}>' for i in range(self.motion_codebook_size)]
        special_tokens = ['<start_of_motion>', '<end_of_motion>', '<masked_motion>', '<pad_motion>']
        self.tokenizer.add_tokens(motion_tokens)
        self.tokenizer.add_special_tokens({'additional_special_tokens': special_tokens})
        
        # Build language model using transformers GPT2LMHeadModel
        print("Building language model...")
        config = GPT2Config(
            vocab_size=50772,  # 50257 text + 512 motion + 3 special
            n_positions=1024,
            n_embd=768,
            n_layer=12,
            n_head=12,
        )
        self.language_model = GPT2LMHeadModel(config).to(self.device)
        
        # Load weights
        print("Loading language model weights...")
        self._load_weights()
        self.language_model.eval()
        print("Model ready!")
        
    def _load_weights(self):
        """Load language model weights from HuggingFace."""
        from huggingface_hub import hf_hub_download
        
        # Download weights
        weights_path = hf_hub_download(
            repo_id="zy22b/GeoMotionGPT",
            filename="model.safetensors"
        )
        
        state_dict = load_file(weights_path)
        
        # Map weights to model (remove 'language_model.' prefix)
        new_state_dict = {}
        for k, v in state_dict.items():
            if k.startswith("language_model."):
                new_key = k[len("language_model."):]
                new_state_dict[new_key] = v
            
        self.language_model.load_state_dict(new_state_dict, strict=False)
    
    def motion_tokens_to_string(self, tokens: torch.Tensor) -> str:
        """Convert motion token IDs to string format."""
        token_list = tokens[0].cpu().tolist()
        mot_start = f'<motion_id_{self.motion_codebook_size}>'      # <start_of_motion>
        mot_end = f'<motion_id_{self.motion_codebook_size + 1}>'    # <end_of_motion>
        motion_str = ''.join([f'<motion_id_{int(t)}>' for t in token_list])
        return mot_start + motion_str + mot_end
    
    def generate_text(self, motion: np.ndarray, mean: np.ndarray, std: np.ndarray, 
                      max_new_tokens: int = 40) -> str:
        """
        Generate text description from motion sequence.
        
        Args:
            motion: Raw motion array of shape (T, 263)
            mean: Mean for normalization (263,)
            std: Std for normalization (263,)
            max_new_tokens: Maximum tokens to generate
            
        Returns:
            Generated text description
        """
        # Normalize motion
        motion_norm = (motion - mean) / std
        motion_tensor = torch.FloatTensor(motion_norm).unsqueeze(0).to(self.device)
        
        # Tokenize motion
        with torch.no_grad():
            motion_tokens = self.motion_tokenizer.encode(motion_tensor)
        
        # Convert to string and create prompt
        motion_string = self.motion_tokens_to_string(motion_tokens)
        prompt = f"Generate text: {motion_string} \n "
        
        # Tokenize prompt
        input_ids = self.tokenizer.encode(prompt, return_tensors="pt").to(self.device)
        
        # Generate using GPT2's built-in generate
        with torch.no_grad():
            output_ids = self.language_model.generate(
                input_ids,
                max_new_tokens=max_new_tokens,
                do_sample=False,
                eos_token_id=self.tokenizer.eos_token_id,
                pad_token_id=self.tokenizer.pad_token_id,
            )
        
        # Decode output
        generated_ids = output_ids[0, input_ids.shape[1]:]
        
        # Filter to text tokens only
        text_ids = [tid.item() for tid in generated_ids if tid.item() < self.text_vocab_size]
        generated_text = self.tokenizer.decode(text_ids, skip_special_tokens=True)
        
        return generated_text.strip(), motion_tokens[0].tolist()


if __name__ == "__main__":
    import argparse
    
    parser = argparse.ArgumentParser(description="GeoMotionGPT Motion-to-Text Generation")
    parser.add_argument("--motion_file", type=str, required=True,
                        help="Path to HumanML3D motion .npy file")
    parser.add_argument("--mean_file", type=str, default="Mean.npy",
                        help="Path to Mean.npy")
    parser.add_argument("--std_file", type=str, default="Std.npy", 
                        help="Path to Std.npy")
    parser.add_argument("--device", type=str, default="cuda",
                        help="Device to use (cuda/cpu)")
    args = parser.parse_args()
    
    # Initialize generator
    generator = GeoMotionGPTGenerator(device=args.device)
    
    # Load data
    motion = np.load(args.motion_file)
    mean = np.load(args.mean_file)
    std = np.load(args.std_file)
    
    print(f"\nInput motion shape: {motion.shape}")
    
    # Generate text
    text, tokens = generator.generate_text(motion, mean, std)
    
    print(f"Motion tokens ({len(tokens)}): {tokens}")
    print(f"\nGenerated text: {text}")

Example Usage:

python geomotiongpt_inference.py \
    --motion_file datasets/humanml3d/new_joint_vecs/000000.npy \
    --mean_file datasets/humanml3d/Mean.npy \
    --std_file datasets/humanml3d/Std.npy

Expected Output:

Loading motion tokenizer from HuggingFace...
Loading GPT2 tokenizer...
Building language model...
Loading language model weights...
Model ready!

Input motion shape: (116, 263)
Motion tokens (14): [138, 104, 508, 21, 498, 229, 144, 484, 393, 393, 144, 144, 144, 414]

Generated text: a person kicks something with their left foot.

Model Architecture

GeoMotionGPTForCausalLM
├── motion_tokenizer (MotionTokenizer)
│   ├── quantizer (MotionQuantizer)
│   │   └── 1D CNN with ResNet blocks
│   ├── decoder (MotionDecoder) 
│   │   └── 1D Transposed CNN with ResNet blocks
│   └── codebook
│       └── 512-entry codebook
└── language_model (GPT2LMHeadModel)
    └── 12-layer transformer

Training Details

• Motion Tokenizer: Trained on HumanML3D dataset with DVQ-GSST quantization
• Language Model: Fine-tuned GPT-2 with:
  • Orthogonality loss (λ=0.01) for motion token embeddings
  • Codebook-initialized motion embeddings
  • AdamW optimizer (lr=1e-4)

Citation

If you use this model, please cite:

@misc{ye2026geomotiongpt,
      title={GeoMotionGPT: Geometry-Aligned Motion Understanding with Large Language Models}, 
      author={Zhankai Ye and Bofan Li and Yukai Jin and Shuoqiu Li and Wei Wang and Yanfu Zhang and Shangqian Gao and Xin Liu},
      year={2026},
      eprint={2601.07632},
      archivePrefix={arXiv},
      primaryClass={cs.CV},
      url={https://arxiv.org/abs/2601.07632}, 
}

License

MIT License