beginners... sheesh!

[RipVege]

Dr Erickson: Thanks for making this package available. I have high hopes for using it.

I'm a riparian biologist; not a programmer. I'm trying to use GapFraction to assess forest shading on streams. I've created a LAS object which is a 100m diameter plot of normalized height points around one of my hemispherical photo test plots. I've installed the lidR and GapFraction libraries, and I can run the p.hv function on the test data provided in the GapFraction package, but when I try to run it on my test plot data I get the message:

P.hv(testPlot4)
Error in h(simpleError(msg, call)) :
error in evaluating the argument 'i' in selecting a method for function '[': object of type 'S4' is not subsettable
In addition: Warning message:
In is.na(eval(las)) : is.na() applied to non-(list or vector) of type 'S4'

I've tried several configurations of the input data (select xyzir is current) , but I think this error is more basic than that. My testPlot4 is a LAS object. is that the correct input?