add Visvalingam ref

paper.bib

@@ -91,3 +91,14 @@
   url = {http://demonstrations.wolfram.com/AdaptivePlotting/},
   urldate = {2019-09-10}
 }
+
+@inproceedings{visvalingam1990douglas,
+  title={The Douglas-Peucker Algorithm for Line Simplification: Re-evaluation through Visualization},
+  author={Visvalingam, Mahes and Whyatt, J Duncan},
+  booktitle={Computer Graphics Forum},
+  volume={9},
+  number={3},
+  pages={213--225},
+  year={1990},
+  organization={Wiley Online Library}
+}

paper.md

@@ -95,6 +95,7 @@ It easily integrates with the Jupyter notebook environment and provides tools fo
 ## Line simplification loss
 
 #### The line simplification loss is based on an inverse Visvalingam’s algorithm.
+Inspired by a method commonly employed in digital cartography for coast line simplification, we construct a loss function that does its reverse. [@visvalingam1990douglas]
 <!-- https://bost.ocks.org/mike/simplify/ -->
 
 ## A parallelizable adaptive integration algorithm based on cquad