RvtkStatismo: Store your models as external pointers

In RvtkStatismo, statistical shape models are stored as objects of class pPCA and in each call of the underlying statismo functions are converted to StatisticalModel<vtkPolyData> and back, which duplicates memory and reduces speed (not very much, but still …). As I got comfortable with Rcpp’s external pointers (see my recent post), I decided to dump boost::shared_ptr in favor of Rcpp::XPtr with the additional benefit that the pointer can now be directly exposed to R. Pointers to shape models are stored in the newly introduced class pPCA_pointer and methods are added to access and process these objects. For the user it does not make any differences whether dealing with pPCA or pPCA_pointer, except that the pointers can’t be saved in the R work-space (however, using statismoSaveModel is more efficient anyway). The functions statismoBuildModel, statismoLoadModel, statismoConstrainModel and statismoBuildConditionalModel, now have the additional option pointer and return, if pointer=TRUE, an object of class pPCA_pointer.

EDIT: The functions pPCA2pointer and pointer2pPCA allow for convenient conversion between the classes pPCA and pPCA_pointer.

In order to install and test the new features you need to:

1. The development branch of statismo (ubuntu 14.04 users can install it from my ppa:

   sudo apt-add-repository ppa:zarquon42/statismo-develop	   
   sudo apt-get update   
   sudo apt-get install statismo
   

2. the development branch of RvtkStatismo In R issue:

   devtools::install_github("zarquon42b/Rvtkstatismo",ref="develop")