Dissolving Logic for Upstream Watershed Boundary Given LINKNO/streamID

[ptomasula]

Summary

With the modified nest set index now implemented (MSNI) (see #3), the next step is to develop logic to utilize the MSNI to rapidly delineate a watershed polygon given the LINKNO/streamID for a reach. Some of the logic for how to utilize the MNSI is provided in this section of the README file.

The task for this issue is to develop the delineation logic and return a single polygon representing the upstream watershed of a provided reach id (LINKNO/streamID)

Closure Criteria

• Function developed for subsetting the network based on modified nest set index
• Function to combining (dissolving) subset of basins into a single polygon
• Tests developed to verify resultant polygon matches known result
• Performance of logic has been tested and characterized

[ptomasula]

In exploring performance for some of the dissolve logic, it seems likely that we will need to implement some sort of pre-dissolve layer to maintain an acceptable level of performance for larger watersheds. I'll open a new issue to for the development of that logic, though I do provide a draft implementation in 0ab4609.