I have a requirement to use the post_visid_high and post_visid_low from Adobe, but I don't exactly know where to find it.
Is ADMS_Measurement.sharedInstance(context).getVisitorID() the same thing? Should I divide it in half to obtain the high and the lower part of post_visid_high/low?
No you won't be able to. What you can send is either the default aid or the marketing cloud visitor ID mid.
Retrieves the Marketing Cloud visitor ID from the visitor ID service.
default visitor ID:
Returns the automatically generated visitor identifier for Analytics.
This is an app-specific unique visitor ID that is generated at the initial launch and is stored and used from that point forward. The ID is preserved between app upgrades, and when the app is uninstalled, it is removed.
But is it possible to extract these 2 values from the Android library directly? I mean I need to send these values to another platform directly from the Android device. Can this be done without involving Data Feed?
You will need to extract Data Feed to find this value. When you said a server call, there is a logic that decide which visitor ID to use. The value that you send for the visitor ID is converted to base10 I believe.