Plots interactive 3D plot for density of detected calls
against call length (s) and principal frequency (kHz), using bivariate
kernel density estimation provided via the MASS package
     
    
    Usage
    plotSurface(data_path, res = 60)
 
    
    Arguments
    - data_path
- The path to the call data 
- res
- The resolution to render surface plot (default is 60) 
 
    
    Value
    
3D surface plot for the selected call dataset
     
    
    Examples
    if (FALSE) plotSurface(data_path = "path")