Visualize the images.txt results generated in COLMAP

      When scripts/colmap2nerf.py is executed in instant-ngp, an images.txt file will be generated in the colmap_text directory, and each two lines in this file define the information of an image:

IMAGE_ID, QW, QX, QY, QZ, TX, TY, TZ, CAMERA_ID, NAME
POINTS2D[] as (X, Y, POINT3D_ID)

      The second line is the position of the key point (feature point), which is the result of executing "colmap bundle_adjuster", specified in pixel coordinates: if the 3D point identifier (3D point identifier) ​​is -1, it indicates that this key point has not been observed in the reconstruction (observe) to a 3D point.

      Here we take lego as an example, that is, after executing colmap2nerf.py on lego, draw the key point information in images.txt in the image and observe the accuracy. The test code is as follows:

import cv2
import sys
import os
from inspect import currentframe, getframeinfo

def parse_txt(txt_name):
    coordinates = []
    images_name = []

    with open(os.path.join(txt_name), "r") as f:
        i = 0
        for line in f:
            line = line.strip()
            if line[0] == "#":
                continue

            i = i + 1
            if  i % 2 == 1: # get image name
                elems = line.split(" ") # 1-4 is quat, 5-7 is trans, 9ff is filename (9, if filename contains no spaces)
                images_name.append(str(f"{'_'.join(elems[9:])}"))
            if i % 2 == 0: # get coordinates
                elems = line.split(" ")
                if len(elems) % 3 != 0:
                    print(f"Error: image name: {images_name[i//2 - 1]}, 2d point(X, Y, POINT3D_ID): {len(elems)}, LINE: {getframeinfo(currentframe()).lineno}")
                    sys.exit(1)
        
                coordinates.append(elems)

        if len(images_name) != len(coordinates):
            print(f"Error: length unmatch: {len(images_name) != len(coordinates)}, LINE: {getframeinfo(currentframe()).lineno}")
            sys.exit(1)

    return images_name, coordinates

def draw_circle(images_name, corrdinates, images_path, result_path):
    for index in  range(len(images_name)):
        img = cv2.imread(images_path+images_name[index])
        if img is None:
            print(f"Error: fail to imread: {images_path+images_name[index]}, LINE: {getframeinfo(currentframe()).lineno}")
            sys.exit(1)

        points = [] # (X,Y)
        ids = []

        for i in range(len(coordinates[index])):
            if i % 3 == 2:
                ids.append(int(str(corrdinates[index][i])))
            else:
                points.append(float(str(corrdinates[index][i])))

        if len(points) != len(ids) * 2:
            print(f"Error: length unmatch: {len(points)}:{len(ids)}, LINE: {getframeinfo(currentframe()).lineno}")
            sys.exit(1)

        count = 0
        for i in range(len(ids)):
            if ids[i] != -1:
                count = count + 1
                img = cv2.circle(img, (int(points[2*i]), int(points[2*i+1])), 2, (0,0,255), -1)

        os.makedirs(result_path, exist_ok=True)
        cv2.imwrite(result_path+images_name[index], img)
        #cv2.imshow("image", img)
        #cv2.waitKey(0)
        print(f"image:{images_name[index]}, total points: {len(ids)}, valid points: {count}")

if __name__ == "__main__":
    txt_name = "test_data/lego/colmap_text/images.txt"
    images_name, coordinates = parse_txt(txt_name)

    images_path = "test_data/lego/train/"
    result_path = "test_data/lego/result/"
    draw_circle(images_name, coordinates, images_path, result_path)

    print("test finish")

      The terminal output is as follows:

      The output for one of the images looks like this:

      GitHub：https://github.com/fengbingchun/Python_Test