Different data structures to represent layers

[mpmisko]

This pull request contains different data structures to represent active points in a layer. These include

• Google dense hash map
• std unordered map
• Lexicographically ordered boost vector
• Custom kd-tree structure using nanoflann. The tree is implemented on top of a hash map pointing to vector elements representing data (for fast indexing and general hash map operations)
• Spatially indexed tree of depth one. To access regions, we use a Google dense hash map. To access within regions, we use point offsets within a region to access a vector.

To select the appropriate data structure modify the Metadata.h header.

[facebook-github-bot]

Thank you for your pull request. We require contributors to sign our Contributor License Agreement, and yours has expired.

Before we can review or merge your code, we need you to email [email protected] with your details so we can update your status.