Warn users that if a dataset has no GPS info, but split-merge is enabled

[pierotofy]

split-merge either needs GPS info or a image_groups.txt file to split a dataset.

Otherwise it cannot work. The program should help users understand that instead of failing with :

OpenCV Error: Assertion failed (data0.dims <= 2 && type == CV_32F && K > 0) in kmeans, file /code/SuperBuild/src/opencv/modules/core/src/matrix.cpp, line 2701
Traceback (most recent call last):
  File "/code/SuperBuild/src/opensfm/bin/opensfm", line 34, in <module>
    command.run(args)
  File "/code/SuperBuild/src/opensfm/opensfm/commands/create_submodels.py", line 30, in run
    self._cluster_images(meta_data, data.config['submodel_size'])
  File "/code/SuperBuild/src/opensfm/opensfm/commands/create_submodels.py", line 100, in _cluster_images
    labels, centers = tools.kmeans(positions, K)[1:]
  File "/code/SuperBuild/src/opensfm/opensfm/large/tools.py", line 34, in kmeans
    return cv2.kmeans(samples, nclusters, criteria, attempts, flags)
cv2.error: /code/SuperBuild/src/opencv/modules/core/src/matrix.cpp:2701: error: (-215) data0.dims <= 2 && type == CV_32F && K > 0 in function kmeans

[theoway]

@pierotofy I'd love to make a PR. Here's how I'm thinking of solving it. If you approve it, I'll make the changes then :)

• Add a member variable self.has_geotagged_photos and a function has_gps() that indicates if GPS info is available.
  

  ODM/opendm/types.py

  Lines 94 to 95 in 6fee4be

  	def has_gcp(self):
  	return self.is_georeferenced() and self.gcp is not None and self.gcp.exists()

• Perform a check here:
  

  ODM/stages/splitmerge.py

  Lines 25 to 32 in 6fee4be

  	def process(self, args, outputs):
  	tree = outputs['tree']
  	reconstruction = outputs['reconstruction']
  	photos = reconstruction.photos
  	outputs['large'] = len(photos) > args.split
  	if outputs['large']:

  
  Something like:

if reconstruction.is_georeferenced() and reconstruction.has_geotagged_photos():
    #perform actions
else:
    #log warning or exit

[pierotofy]

Sounds like a good approach!

[theoway]

Sounds like a good approach!

Could you tell me what would be better? Exiting the process or just logging a warning?

[pierotofy]

I would print a warning and try to process the dataset without split-merge.