Smooth the simplified flowline.

[donghuix]

Currently, the simulated flowline has different distance between two adjacent vertices. The distance can be very long over some parts of the flowline, which will result in abrupt change for the channel elevation when deriving the channel slope. It will be useful to add a feature to smooth the simulated flowline, and the user can provide an threshold to determine the minimum distance between any two adjacent vertices.

[changliao1025]

To support this feature, we will add a new algorithm to automatically break an edge into multiple edge if its length exceeds the user provided threshold.
The algorithm will split the edge by two recursively until each sub edge is shorter than the threshold.
The algorithm will be implemented following some discussion from here:

https://gis.stackexchange.com/questions/55166/how-to-calculate-midpoint-given-north-south-latitude-and-east-west-longitude

The algorithm works on a sphere.

[changliao1025]

Pyflowline now has an experiment algorithm to support this feature. The model will scan the simplified flowline and identify the edges (defined by a starting and ending point) that exceed the length threshold. It splits the edge by the middle point one or more times depending on the final length. Other components may also use vector-based algorithms.