public void AppendFacets()
{
STLDocument stl1 = null;
STLDocument stl2 = null;
int facetCount = 0;
using (Stream stream = GetData("ASCII.stl")) {
stl1 = STLDocument.Read(stream);
stl2 = STLDocument.Read(stream);
}
ValidateSTL(stl1);
ValidateSTL(stl2);
facetCount = (stl1.Facets.Count + stl2.Facets.Count);
stl1.AppendFacets(stl2);
ValidateSTL(stl1, facetCount);
}