Using geos inside a Rcpp function

Question

Anyone have a hint in how to use geos inside Rcpp functions (I'm building an R package)? Actually, I'm looking for a better approach then this:

Rcpp::Environment rgeos_env = Environment::namespace_env("rgeos");
Rcpp::Function Dist = rgeos_env["gDistance"];

Contextualizing, I want to calculate distances between spatial polygons, but I do that a lot of times (Monte Carlo Tests) and I want to improve the speed of my code.

You will not gain any speed up calling an _R_ function from _Rcpp_. This is because you have to _stop_ the _C++_ execution, pass objects back to _R_, run the _R_ function, export the results back into _C++_, and then finish the computation. Overall, there is a lot more overhead for little gain. — coatless, Apr 08 '18 at 23:53
Have you tried using the `sf` package which uses `geos` to do spatial calculations? — SymbolixAU, Apr 09 '18 at 00:03
@SymbolixAU, I tried last year, but it was slower than what I had. Thank you for the suggestion. — lcgodoy, Apr 09 '18 at 00:25
It is a _qualitative_ duplicate in the sense that you cannot possibly envision Monte Carlo replications around _calling an R function_ from C++ and somehow betting on the magic pony to make it faster than R. — Dirk Eddelbuettel, Apr 09 '18 at 00:32

score 1 · Accepted Answer · answered Apr 09 '18 at 07:52

1

I see two possible approaches to use geos without going back to R from C++:

Try to link with the rgeos package, c.f. using C function from other package in Rcpp
Do what the rgeos package does, i.e. link with the geos library and call the relevant functions, c.f. https://github.com/cran/rgeos/blob/28403d4d4adbc3bd76c11e4c55dec7e097d74f6d/src/rgeos_misc.c#L50

answered Apr 09 '18 at 07:52

Ralf Stubner

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Thank you for the suggestions, it was very helpful. – lcgodoy Apr 09 '18 at 12:47

Using geos inside a Rcpp function

1 Answers1