Retrieves the graph a graphical population originate from
popsRetrieveGraph(obj, pops, vis2D = "density", all_siblings = FALSE)
an `IFC_data` object extracted by ExtractFromDAF(extract_features = TRUE) or ExtractFromXIF(extract_features = TRUE).
names of graphical populations present in 'obj'. Note that they should be siblings.
when original graph is not an histogram, whether to display it as "scatter" or "density". Default is "density".
whether to add all 'pop' siblings in the graph. Default is FALSE.
a list of parameters needed to build an IFC graph.