Added center, centroid and envelope.
Added center, centroid and envelope.

nbumbarger/dropchop,tgirgin23/dropchop,nbumbarger/dropchop,tgirgin23/dropchop,tgirgin23/dropchop,jrrembert/drop-n-chop,cugos/dropchop,jrrembert/drop-n-chop,nbumbarger/dropchop,cugos/dropchop,jrrembert/drop-n-chop