Question: Merge function fails due to the "transform" key not being found

[rob-scholten95]

I have been trying to merge four tiles, downloaded through WFS in Blender:

3DBAG tiles:
['9/248/576', '9/248/580', '9/252/576', '9/252/580']

The code i use for loading in the file to be read:

with open(filename, 'r', encoding='utf-8') as file:
	cityjson_cm = cjio.cityjson.load(filename, True)

Now, in this file, I have verified multiple times that there is no "transform" key in the file. Now when I load it in as an normal JSON,

with open(filename, 'r', encoding='utf-8') as file:
	cityjson_cm = cjio.cityjson.load(filename, True)

the 'transform' key does exist. The key also exists when I download the tile from the WFS service:

try:
	response = requests.get(url)
							
	with open(fname, "wb") as file:
		data = response.content
		file.write(data) 
		fnames.append(fname)
			
	except urllib.error.HTTPError as err:
              print(err)

This is the output:

CityJSON version = 2.0
EPSG = 7415
bbox = [ 75588.586 450907.906 -1.835 76602.266 451895.625 56.600 ]
=== CityObjects ===
|-- Building (1663)
    |-- BuildingPart (1668)
===================
materials = False
textures = False
CityJSON version = 2.0
EPSG = 7415
bbox = [ 75585.469 451852.469 -0.438 76606.789 452902.656 45.454 ]
=== CityObjects ===
|-- Building (3555)
    |-- BuildingPart (3557)
===================
materials = False
textures = False
CityJSON version = 2.0
EPSG = 7415
bbox = [ 76529.047 450881.562 -3.081 77629.922 451934.500 41.518 ]
=== CityObjects ===
|-- Building (1372)
    |-- BuildingPart (1374)
===================
materials = False
textures = False

of this code:

with open(filename, 'r', encoding='utf-8') as file:
			#json_cm = json.load(file)
			#print(json_cm['transform'])
			
			cityjson_cm = cjio.cityjson.load(filename, True)
			print(cityjson_cm)

this is the collapsed structure of the downloaded JSON file, where the transform key is visible:

I am probably missing something, but i am desperate. Any help would be greatly appreciated!

[hugoledoux]

It's loaded but it's not printed by that function.

If you do this you should see it:

print(cityjson_cm.transform)

See there how to use it:
https://cjio.readthedocs.io/en/latest/api_tutorial_basics.html#Geometry-boundaries-and-Semantic-Surfaces

Hope this helps

[rob-scholten95]

Hey!

thanks for your help! I can now see the 'transform' information using the solution you proposed. I still can't get it to work properly when trying to merge the different tiles together using merge().

def merge_city_json(filenames):
	
	cms = []

	cm = cityjson.load(filenames[0], transform=True)
	print(f"Loaded a citymodel with {len(cm.cityobjects)} CityObjects")
		
	for p in filenames[1:]:
		_cm = cityjson.load(p, transform=True)
		cms.append(_cm)
		print(f"Loaded a citymodel with {len(_cm.cityobjects)} CityObjects")
			
	cm.merge(cms)  

it results in this error:

Python: Traceback (most recent call last):
  File "F:\Projects\00_Documents\JSON\JSON import using python4.1.blend\Text", line 247, in <module>
  File "F:\Projects\00_Documents\JSON\JSON import using python4.1.blend\Text", line 245, in main
  File "F:\Projects\00_Documents\JSON\JSON import using python4.1.blend\Text", line 172, in merge_city_json
  File "C:\Users\Rob\AppData\Roaming\Python\Python311\site-packages\cjio\cityjson.py", line 1263, in merge
    imp_digits = math.ceil(abs(math.log(self.j["transform"]["scale"][0], 10)))
                                        ~~~~~~^^^^^^^^^^^^^
KeyError: 'transform'

[rob-scholten95]

Still trying to figure this out. On my work machine it works flawlessly, but on my personal machine it always stops with this error. I have double checked the versions and have made multiple venv's with the requirements.txt from my work PC's venv. Anyone any clue?

[balazsdukai]

Hi @rob-scholten95 , could you try:

def merge_city_json(filenames):
	
	cms = []

	cm = cityjson.load(filenames[0], transform=False)
	print(f"Loaded a citymodel with {len(cm.cityobjects)} CityObjects")
		
	for p in filenames[1:]:
		_cm = cityjson.load(p, transform=True)
		cms.append(_cm)
		print(f"Loaded a citymodel with {len(_cm.cityobjects)} CityObjects")
			
	cm.merge(cms)  

You'll find some more material here: https://github.com/3DGI/3dbag-workshop-foss4gnl2021 . The workshop explains how the different parts of cjio work together at the moment.