Merge branch 'hexagon_projections' (PR #626)

This merge removes an instance of a hard-wired earth radius in project_hexes,
addressing a potential inconsistency that could lead to Cartesian coordiantes of
elements that do not lie on the surface of the unit sphere. In turn, this could
lead, for example, to failures when processing static fields in the MPAS-Model
init_atmosphere core. Now, the user-specified earth_radius_km value is used
consistently throughout the code where a sphere radius value is required.

Author: mgduda

mesh_tools/hex_projection/project_hexes.f90

@@ -57,7 +57,7 @@ program project_hexes
   integer, allocatable, dimension(:) :: indexToCellID, indexToVertexID, indexToEdgeID
 
   real(dp), allocatable, dimension(:) :: dcEdge, dvEdge
-  real(dp), parameter :: earth_radius = 6378.14_dp*1000.0_dp  ! meters
+  real(dp) :: earth_radius
   real(dp) :: invRadius, invRadius2
 
   real(dp) :: nominalMinDc
@@ -878,6 +878,7 @@ program project_hexes
 
   ! set mesh on a unit sphere - this is what init_atmosphere expects - it will expand it to the full sphere.
 
+  earth_radius = 1000.0_dp*earth_radius_km
   invRadius = 1.0_dp/earth_radius
   invRadius2 = invRadius*invRadius