Table Top Camera - How do I start?

I have used Roll 20 for a few months using Marketplace maps and others found on the web but would rather use the 3D terrain and a webcam.   A loaded question but how do I get started?  Any helpful videos out there I can check out?  I've looked an haven't had much luck - possibly using wrong terminology.  Any help would be appreciated.   Thanks in advance!  

It sounds like you want to overlay the Roll20 VTT over a livestream webcast? That isn’t possible with Roll20. If I’m misunderstanding let me know. 

Hmmm...   Maybe not smart enough to know the terminology.  Not looking to broadcast or livestream the game. Just wanting to show a 3D map to players (one I would build and then show via a camera - allowing for real time movement of 3D figure) I appreciate the response.  Hopefully I've provided more info as to what I am trying to do and if it is possible.  

You mean a physical 3d map and webcam pointed at it (ala Critical Role?) Programs like OBS allow you to have two cameras going at once if you mean you want one on you and one on the map...

Correct.  One camera on me to interact with players and one on the map.  (I guess CR would be a good example - without the broadcast part)

Sounds like a second account might be a simple solution. If my suspicion is correct, you could log in on a different browser (or private browsing window i.e. incognito on chrome), then in the settings in the game, change the video input device to the alternate camera. In this way, you could perform everything using one computer. Additionally, you could likely get everyone in the game to download the Stylus extension and put a rule that applies to the avatar for that account which could resize it to become rather large (since I imagine the sizes provided via Roll20 might not be large enough) and they could simply turn the rule on and off whenever they want to zoom in/out. If that is indeed a route you're interested in taking that is.

Thank you for the 411.  Looks like no direct method to accomplish what I am looking for.  I will have to give your method a try.