I assume the words "Hau ab" and "geh raus" have kind of same meaning. Which one is considered more harsh or strict way to say someone to get out?
Geh raus! comes from rausgehen which in turn comes from herausgehen. In the specified form this is just the imperative, which is not really rude in the literal sense (i.e. offensive). However, it is definitely impolite. It can be turned more polite by adding bitte, i.e. "Gehen Sie bitte (raus)". With the raus, this means the other person has to leave out of some kind of room, building, car, ... .
Hau ab! comes from abhauen which is colloquial and when used in the imperative mood less respectfull / more informal than geh raus!, which in my opinion would qualify as more harsh. This is also more universal, as this does not imply getting out of something (no raus). You can also say this to an animal that is bothering you (although chances you are successful are slim).
A more polite version would be:
Würden Sie bitte gehen? Would you please leave
A rude version (offensive) would be:
Verpiss dich gefälligst! Fuck off already
At the risk of pointing out the obvious: Unless another person is bothering you, it is generally considered impolite to ask someone to leave. You might want hint at it first or use some humor:
Ich glaub ich muss Dich jetzt mal rausschmeißen, es wird langsam spät und ich muss morgen früh raus. (colloquial) I think I need to kick you out now, it's getting late and I have to get up early
If the person then does not leave, you can try the less polite versions.
Geh raus is a friendly way to say you should leave. Hau ab(!) is very harsh and unfriendly.
Geh raus is no real substitute for Hau ab, because there are so many different reasons for going outside, e.g. for smoking.... Note that Sollen wir rausgehen? is a somewhat common invitation for a brawl.
Verschwinde would be a better alternative and while while pretty harsh could also be combined with polite *Sie * addressing.