Upside down models

[JaLnYn]

The output of my gaussian splats seems to be upside down. Here is my colmap script

I saw documentation saying that the data format is different so I've tried flipping the cameras.txt and points3d.txt over the x axis manually but the gaussians remain upside down. Anyone with a similar issue? Am I not converting correctly?

import os
import logging
import argparse
import shutil
from pathlib import Path

def run_command(cmd, error_msg="Command failed"):
   exit_code = os.system(cmd)
   if exit_code != 0:
       logging.error(f"{error_msg} with code {exit_code}. Exiting.")
       exit(exit_code)
   return exit_code

def process_dataset(dataset_name):
   script_dir = os.path.dirname(os.path.abspath(__file__))
   unprocessed_dir = os.path.join(script_dir, "data", "unprocessed", dataset_name)
   processed_dir = os.path.join(script_dir, "data", dataset_name)

   if not os.path.exists(unprocessed_dir):
       print(f"Error: Dataset directory {unprocessed_dir} does not exist")
       return False

   os.makedirs(os.path.join(processed_dir, "images"), exist_ok=True)
   os.makedirs(os.path.join(processed_dir, "sparse"), exist_ok=True)
   os.makedirs(os.path.join(processed_dir, "distorted/sparse"), exist_ok=True)

   print("Copying and renaming images...")
   files = sorted(os.listdir(unprocessed_dir))
   for idx, filename in enumerate(files, 1):
       if filename.lower().endswith(('.jpg', '.jpeg', '.png')):
           old_path = os.path.join(unprocessed_dir, filename)
           new_path = os.path.join(processed_dir, "images", f"frame_{idx:05d}.jpg")
           shutil.copy2(old_path, new_path)

   print("Running feature extraction...")
   cmd = f"colmap feature_extractor" \
         f" --database_path {processed_dir}/distorted/database.db" \
         f" --image_path {processed_dir}/images" \
         f" --ImageReader.single_camera 1" \
         f" --ImageReader.camera_model OPENCV"
   run_command(cmd)

   print("Running feature matching...")
   cmd = f"colmap exhaustive_matcher" \
         f" --database_path {processed_dir}/distorted/database.db"
   run_command(cmd)

   print("Running bundle adjustment...")
   cmd = f"colmap mapper" \
         f" --database_path {processed_dir}/distorted/database.db" \
         f" --image_path {processed_dir}/images" \
         f" --output_path {processed_dir}/distorted/sparse" \
         f" --Mapper.ba_refine_focal_length 1" \
         f" --Mapper.ba_refine_principal_point 1" \
         f" --Mapper.ba_refine_extra_params 1"
   run_command(cmd)

   print("Converting model to modify orientation...")
   cmd = f"colmap model_converter --input_path {processed_dir}/distorted/sparse/0 --output_path {processed_dir}/distorted/sparse/0 --output_type TXT"
   run_command(cmd)

   images_file = f"{processed_dir}/distorted/sparse/0/images.txt"
   with open(images_file, 'r') as f:
       lines = f.readlines()
       for i, line in enumerate(lines):
           if line[0].isdigit():
               parts = line.split()
               qw, qx, qy, qz = map(float, parts[1:5])
               qy, qz = -qy, -qz  # 180-degree rotation around X-axis
               parts[1:5] = map(str, [qw, qx, qy, qz])
               lines[i] = ' '.join(parts) + '\n'

   with open(images_file, 'w') as f:
       f.writelines(lines)

   cmd = f"colmap model_converter --input_path {processed_dir}/distorted/sparse/0 --output_path {processed_dir}/distorted/sparse/0 --output_type BIN"
   run_command(cmd)

   print("Running image undistortion...")
   cmd = f"colmap image_undistorter" \
         f" --image_path {processed_dir}/images" \
         f" --input_path {processed_dir}/distorted/sparse/0" \
         f" --output_path {processed_dir}" \
         f" --output_type COLMAP"
   run_command(cmd)

   print("Organizing sparse reconstruction...")
   sparse_dir = os.path.join(processed_dir, "sparse")
   sparse_0_dir = os.path.join(sparse_dir, "0")
   os.makedirs(sparse_0_dir, exist_ok=True)

   for file in os.listdir(sparse_dir):
       if file == '0':
           continue
       source_file = os.path.join(sparse_dir, file)
       destination_file = os.path.join(sparse_0_dir, file)
       if os.path.isfile(source_file):
           shutil.move(source_file, destination_file)

   print("Creating resized versions...")
   img_dir = os.path.join(processed_dir, "images")
   for scale in [2, 4, 8]:
       scaled_dir = os.path.join(processed_dir, f"images_{scale}")
       os.makedirs(scaled_dir, exist_ok=True)
       
       resize_percent = {2: "50%", 4: "25%", 8: "12.5%"}[scale]
       
       for img in sorted(os.listdir(img_dir)):
           if img.lower().endswith(('.jpg', '.jpeg', '.png')):
               src = os.path.join(img_dir, img)
               dst = os.path.join(scaled_dir, img)
               shutil.copy2(src, dst)
               cmd = f"magick mogrify -resize {resize_percent} {dst}"
               run_command(cmd)

   print("Processing complete!")
   return True

def main():
   parser = argparse.ArgumentParser(description="Process dataset through COLMAP pipeline")
   parser.add_argument("dataset_name", help="Name of the dataset")
   args = parser.parse_args()
   
   process_dataset(args.dataset_name)

if __name__ == "__main__":
   main()

[CaptainArmenia]

I am experiencing exactly the same issue:

This makes the visualization really uncomfortable, as it is impossible to flip it upside-down.

[JaLnYn]

I think it's a visualizer issue? It works when I use nerfstudio splat with the same data.

[brentyi]

If you pip install --upgrade viser there should be a tool for reorienting the viewer. Relevant PR: nerfstudio-project/viser#361

The align_principle_axes function is a possible root cause of this problem: https://github.com/search?q=repo%3Anerfstudio-project%2Fgsplat%20align_principle_axes&type=code