Hi Jeremy,The most simple solution I found for now is to place forward declarations of hemisphere and your intersects() overloads before #include<boost/geometry.hpp>, so:
Note that hemisphere doesn't have to be defined in the bg::model namespace and that traits are not needed.
P.S. you have a bug here: https://github.com/jeremy-murphy/concave_hull/blob/ master/hemisphere.hpp#L48
You're passing a point to a 2-argument set() function which is used for segments and boxes. Either remove the first argument or pass segment instead of a point.