Implement a network validation/comparison framework

[benducke]

A way to validate (or compare) the output of v.net.models is required. This would best be implemented as a separate module (v.net.validate):

Some ideas:

• Measure fit with markers (proxy evidence).
• Measure fit with (partial) observations of links and nodes.
• Measure fit with assumptions (max. link length, max. connections per node, ...)
• Stability analysis.
• ...

[benducke]

Network similarity metrics might be useful for network comparison (global):

• Similiarity of Connectivity (compare connectivity matrices)
• Similarity of Shape (total/mean/median length; shape indices, ...)
• Similarity of Fit (distance from markers)

[benducke]

Relative assymetry: How many nodes have to be traversed on average to get from any to any node?