They would not expect you to fly the ODP on you own accord nor should you presume that it is part of a clearance unless otherwise advised.
Of course, that's not what the AIM says. From AIM 5.2:
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ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC. "
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Or maybe the Pilot/Controller Glossary will help. You know, the one that's part of both the AIM and the ATC Manual?
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OBSTACLE DEPARTURE PROCEDURE (ODP)- A preplanned instrument flight rule (IFR) departure procedure printed for pilot use in textual or graphic form to provide obstruction clearance via the least onerous route from the terminal area to the appropriate en route structure. ODPs are recommended for obstruction clearance and may be flown without ATC clearance unless an alternate departure procedure (SID or radar vector) has been specifically assigned by ATC.
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On the other hand, your controller stared the conversation by saying he didn't know what you were talking about.
Hmmmm. Specific information in the AIM vs. a controller who claims to be clueless. I wonder which one I will rely on.
In a radar environment, the difference won't matter since ATC will almost always issue a radar vector or alternate departure procedure, which negates the ODP.
But if you are =not= given vectors after takeoff or another departure procedure and you don't follow the ODP because no one specifically told you to, we could be reading about you in an interesting NTSB report, all wondering why this instrument pilot had a CFIT accident when there was a printed procedure to keep him out of the rocks.