scale_analysis.py

import trimesh
import numpy as np
import os
import sys

def analyze_sizes(obj1_path, obj2_path):
    """Analyze size differences between two OBJ files"""
    
    # Check if files exist
    if not os.path.exists(obj1_path):
        print("Error: File {} not found".format(obj1_path))
        return
    if not os.path.exists(obj2_path):
        print("Error: File {} not found".format(obj2_path))
        return
    
    # Load meshes
    print("Loading {}...".format(obj1_path))
    mesh1 = trimesh.load(obj1_path)
    print("Loading {}...".format(obj2_path))
    mesh2 = trimesh.load(obj2_path)
    
    # Get dimensions
    dim1 = mesh1.bounds[1] - mesh1.bounds[0]
    dim2 = mesh2.bounds[1] - mesh2.bounds[0]
    
    # Calculate scale ratios (how much bigger/smaller mesh2 is compared to mesh1)
    scale_ratios = dim2 / np.maximum(dim1, 1e-8)
    
    # Calculate volume and area ratios
    volume_ratio = mesh2.volume / max(mesh1.volume, 1e-8)
    area_ratio = mesh2.area / max(mesh1.area, 1e-8)
    
    # Output results
    print("\nSize Analysis Results:")
    print("-" * 50)
    print("Mesh 1 ({}):".format(os.path.basename(obj1_path)))
    print("  Dimensions (XYZ): {:.4f} x {:.4f} x {:.4f}".format(dim1[0], dim1[1], dim1[2]))
    print("  Volume: {:.4f}".format(mesh1.volume))
    print("  Surface Area: {:.4f}".format(mesh1.area))
    
    print("\nMesh 2 ({}):".format(os.path.basename(obj2_path)))
    print("  Dimensions (XYZ): {:.4f} x {:.4f} x {:.4f}".format(dim2[0], dim2[1], dim2[2]))
    print("  Volume: {:.4f}".format(mesh2.volume))
    print("  Surface Area: {:.4f}".format(mesh2.area))
    
    print("\nScaling Factors (Mesh2/Mesh1):")
    print("  X-axis scale factor: {:.6f}".format(scale_ratios[0]))
    print("  Y-axis scale factor: {:.6f}".format(scale_ratios[1]))
    print("  Z-axis scale factor: {:.6f}".format(scale_ratios[2]))
    print("  Average scale factor: {:.6f}".format(np.mean(scale_ratios)))
    print("  Volume ratio: {:.6f}".format(volume_ratio))
    print("  Surface area ratio: {:.6f}".format(area_ratio))
    
    # Check for uniform scaling
    scale_variation = np.std(scale_ratios)
    if scale_variation < 0.01:
        print("\nScaling appears to be uniform across all dimensions")
    else:
        print("\nNon-uniform scaling detected - different scaling in different dimensions")
        print("Scale variation (std dev): {:.6f}".format(scale_variation))
    
    # Interpretation
    print("\nInterpretation:")
    print("- Scale factor > 1: The second mesh is larger than the first")
    print("- Scale factor < 1: The second mesh is smaller than the first")
    print("- Non-uniform scaling means the object's proportions differ between meshes")

if __name__ == "__main__":
    if len(sys.argv) != 3:
        print("Usage: python scale_analysis.py [reference_obj_file] [comparison_obj_file]")
        sys.exit(1)
    
    analyze_sizes(sys.argv[1], sys.argv[2])