Hold on here. You don't need data from the game client to pinpoint a location on a planet, all you really need is the coordinates of that location. Therefore, the coordinates of the ship when you land is all you'd need to place a marker that is no different to the way the planetary stations are marked. I understand that you can't record the current coordinates while you're flying since the numbers can change by hundreds every second. In this manner, you would have to physically visit a specific spot in order to mark it. If the coordinates of the ship when it is parked on the ground were stored in the netlog file, we wouldn't be having this conversation and we would be enjoying a very useful addon.
I'm getting a little confused.
If you're suggesting that all we need is to be able to read our parked location when we land, then the Journal already supplies that through with the "Touchdown" event:
Code:
{ "timestamp":"2016-07-22T10:38:46Z", "event":"Touchdown", "Latitude":63.468872, "Longitude":157.599380 }
The problem is, knowing the end location isn't navigation. That would be like suggesting we don't need a GPS in our car because we know the address of where we're going. A navigation system needs to direct you to that location and to do that it needs to know (at a reasonably steady rate) where you currently are in relation to the destination.
The Surface Navigation module uses constant positional updates to provide such guidance and mapping.