Helper function factory to classify morphometric features according to a modified version of Wood 1996 page 120
     
    
    Usage
    classify_features_ff(slope_tolerance = 1, curvature_tolerance = 1e-04)
 
     
    
    Arguments
- slope_tolerance
 
Slope tolerance that defines a 'flat' surface (degrees; default is 1.0). Relevant for the features layer.
 
- curvature_tolerance
 
Curvature tolerance that defines 'planar' surface (default is 0.0001). Relevant for the features layer.
 
 
    
    Value
    A function that can be passed to raster::overlay to classify morphometric features
     
    
    References
    Wood, J., 1996. The geomorphological characterisation of digital elevation models (Ph.D.). University of Leicester.