How the "gSymdifference" of rgoes package calculating the symmetric distance between two polygon

Dear all,

I want to calculate the symmetric distance between two polygon. I learned
that "gSymdifference" and "gArea" of "rgoes" can be used for that purpose.
But I am not getting how this difference is calculated (what are R-codes).

The code I am getting by straight forward typing the "gSymdifference" is
giving me:
function (spgeom1, spgeom2, byid = FALSE, id = NULL, drop_lower_td = FALSE,
unaryUnion_if_byid_false = TRUE, checkValidity = FALSE)
{
if (checkValidity) {
val1 <- gIsValid(spgeom1)
val2 <- gIsValid(spgeom2)
if (!val1)
message(deparse(substitute(spgeom1)), " is invalid")
if (!val2)
message(deparse(substitute(spgeom2)), " is invalid")
if (!all(c(val1, val2)))
stop("Invalid objects found")
}
return(RGEOSBinTopoFunc(spgeom1, spgeom2, byid, id, drop_lower_td,
unaryUnion_if_byid_false, "rgeos_symdifference"))
}
<environment: namespace:rgeos>

The above is not helping for this purpose. Where from I can get the codes
of the functions and get to know how the "gSymdifference" and "gArea" is
calculating the difference?

Thanks a lot for your time.

Sincerely,

Kaushik

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