(This is a provisional posting!)
PTK deaspiration is simply that in places where RP has (post)aspiration the
aspiration is lost.
This occurs in the onset of STRESSED syllables, and so in quite different places from Glottalization and glottalisng, which occur AFTER stressed syllables. So pea, tea, cool (pHi: tHi: kHu:l where H = raised h) you get pi: ti: ku:l (which sound like like Ice bí dí gúl) - this is a SAfr accent, and also occurs in Indian accents.