Can you reach any know arbitrary coordinates in the Grand Line without a Log Pose pointing there?

Question

So, when you travel the Grand Line normal navigation methods don't work because of the chaotic nature of place. Compasses just spin randomly, the weather can change without any warning, currents can make a ship change course without the crew even realizing etc.

For this reason, pirates who attempt traveling the Line rely on a Log Pose, a device that always point to a specific "next" island on a specific route. After crossing the Red Line again and entering the "New World" the Log Pose is then upgraded to handle the even worse conditions: we go from a single needle to three (because some island may just "decide" to become unavailable "because reason").

If you keep following the Log Pose you will eventually reach a "Final Island": Lodestar.

And then... your Log Pose stop working. There is no "next" island to point to, so the device you relied up so far suddenly becomes a decorative piece of furniture.

After you reached Lodestar, you are supposed to discover about the existence of the four Road Poneglyph (assuming a random guy on Zou didn't spoil you before). Using the four Road Poneglyph you are supposed to locate four points on the map...

and Laugh Tale is supposed to be found at the intersection of those four points.

So basically, Roger crew:

• followed the Log Pose up to Lodestar.
• somehow managed to "go back" from Lodestar to the previous islands where the four Road Poneglyph were located (without any way to know in advance that they would need to return there).
• used the info from the four Road Poneglyph to find Laugh Tale.
• somehow managed to reach an arbitrary "island" in the middle of nowhere that no existing Log Pose points to in a place where we have been told so far the only way to reach some point is to have something that points there.

Let's assume that Roger was able to "backtrack" in the Grand Line using multiple vibre cards and Eternal Pose that the crew strategically kept on hand during the journey (btw good luck crossing the red line without a Eternal Pose for Fishman Island, apparently that is the only safe place to travel under the mountains) IF the "Laugh Tale is found at the intersection of the four places indicated by the Road Poneglyph" is to be taken literally as the picture above implies (picture actually taken from the show) this means that to reach Laugh Tale you have to reach an arbitrary set of coordinates in the sea, without any modern GPS systemm, without a working compass, in a sea where apparently you can even be sure you are going in a straight line and where star based navigation just doesn't seem to work "good enough" to be usable (for example during the Alabasta arc Chopper mentions he couldn't see any star at night from his home island because of the permanent winter weather conditions, and Enies Lobby is literally stuck in an "eternal day").

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You see where this is going.

How can anyone be able to reach 47°9′S 126°43′W under such conditions? And to be fair... how did all the pirates that "gave up" backtrack the line to return to their home sea (see: Don Krieg, Zeff) - where they just crazy prepared and kept an Eternal Pose for all the mayor island during their journey onward (this would make Nami suddenly look like a pathetic newbie since she is never shown planning for this... it is "forward or die" for the Straw Hats...). Either the inability to reach a set of specified coordinates in the Grand Line is greatly exaggerated or it should be impossible to reach any point you don't have a Log Pose pointing to.

Am I missing some obvious caveat that could explain this? Are my initial assumptions actually wrong? Or should we just accept that this point has no actual explanation right now and may become relevant in the future?

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Short version:

At the start of the Grand Line we are explicitly told that regular compasses don't work and implicitly that celestial / star based navigation doesn't work either because of the extreme chaotic conditions of the place (notice: there is even a place - Enies Lobby - where it is always day) and you have to use Log Pose that points to specific places to get around. Later, under the same restrictions, we are told that to reach Laugh Tale you have to find out its location and then travel to those coordinates without anything that points there.

Is there any indication of how that is possible so far in the plot? How can you reach any point even with a map if we are told that the Log Pose is the only reliable way to know which direction you are going since traditional instruments can't work (sextants, compasses, celestial navigation etc).

Answer 1

One thing to consider are South Birds. It was a big deal during the Jaya arc that the Straw Hats needed to head due South from Jaya to the Knock Up Stream. They couldn't use their log pose because the log pose only points directly at the next island (Skypiea) with no reference to the compass directions. Nor normal compasses which don't work in the Grand Line due to the magnetic fields of the individual islands causing the needle to go crazy. They're told to wrangle a South Bird and leverage its inexplicable ability to always point South.

South Birds clearly have some mechanism which allows them to determine compass directions unaffected by the magnetic fields of the islands of the Grand Line and would be invaluable for navigating the GL without log/eternal poses (E.G. sailing towards an arbitrary set of coordinates) which honestly beggars the question why they aren't more widely used.

Granted just having a working compass is only half the solution, knowing which way is South is well and good but doesn't tell you where you are. This would require tools like astrolabes or sextants which can determine Latitude and Longitude. As far as I recall, we've never seen anyone ever use such tools even though they should work (you only really need it, the sun and the horizon) and they'd be needed to navigate even outside the Grand Line (maps and a compass aren't very useful if you're out at sea and don't know where you are and therefore what direction your destination is). Although, since sailors can navigate the Blues just fine we can probably assume they have some way of knowing where they are, which, supplemented by maps and a compass should be good enough to find a specific spot in the oceans

Answer 2

Four eternal poses should do it. You can use the vectors of the four poses as a low-tech combined GPS system locally from between the four islands. If you can get to at least one of the islands (which having even one eternal pose can help you do) then you can find the one piece if you know the location between the four points on the map. The way you calculate where you are is taking all of the eternal pose vectors and drawing lines from their islands on a map at regular intervals until your four vectors align at the target point. Technically this should be possible even with only three poses. The challenge is that if you need to know the height (or depth) you need a fourth vector to predict a 3D location.

For similar reasons, if they can make use of birds or flying machines they could avoid needing to do any of this and just fly high enough that they can localize the point they're looking for from the sky.

Another way, which you might not have considered is making use of the stillness of the calm belts. If you reach the calm belt and can assess which side of the grand line you are on, you can simply travel straight along the calm belt by using an external force instead of the wind and waves. Presumably then any log pose or compass or other method of navigation should get you back on track regardless of where you end up but there would be no way to know how far you've gotten without some serious engineering work and traditional navigation methods would fail as soon as you entered the grand line again) - another way to localize yourself, a vivre card, or an eternal pose is highly preferable. It is known that various individuals have multiple ways to cross the calm belt from lining ships with seastone to just being incredibly powerful (and able to defeat sea kings). Given the Sunny's ability to launch itself through the air, among other various feats, with some improvements, I suspect it could survive this method.

I should also mention that four vivre cards for four members of the Strawhats or their allies would be sufficient for them to use in place of eternal poses should those individuals head to the four islands. Not sure how this would work for someone like Buggy who can split themselves into multiple pieces. Maybe he could somehow use a vivre card in another way with four parts of himself to find the one piece? Probably easier to use eternal poses though.

Answer 3

Am I missing some obvious caveat that could explain this?

Yes, Maps / Sea Charts. This is what makes Navigators so important to crews even with the existence of Log Poses.

To quote the most relevant parts of the wiki (emphasis mine):

In the world of One Piece, maps are an essential tool for navigation, as they often depict the geography of an individual island, a group of islands or even an entire ocean (in which case, they are sometimes referred as sea charts). In sailing, it is usually the duty of navigators to read and interpret maps during voyages, in order to establish safe navigation routes and avoid natural hazards or getting lost.

The first relevant map shown in the series was one of the Grand Line, which belonged to Buggy, but was stolen by Nami and subsequently used by the Straw Hat Pirates to enter the Grand Line through Reverse Mountain. Another important map was of Skypiea's, which Luffy managed to find in the old remains of the St. Briss and allowed the Straw Hats to consider the idea of Sky Islands.

Nami's entire arc revolves around maps - her dream is to make a map of the entire world, and she was exploited by Arlong due to her great ability to understand and create them.

There may not be any "arbitrary coordinates" in the One Piece world since they don't have GPS, but to reach Laugh Tale based on descriptions from the 4 Road Poneglyphs is exactly what a Navigator is skilled at doing.

This would also explain how Roger's crew backtracked. We don't have confirmation about who on the crew was a Navigator, but since they were the first to circumnavigate the world and find Laugh Tale, it should have been easy to go back the way they came.

Eternal Poses are said to cost a fortune to purchase, so it is probably not used by most crews. Vivre cards do remain a last ditch option, but they only tell you the direction and not anything about distance or obstacles. So it is likely they too would be insufficient / dangerous without some kind of Navigator.

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In the anime, there seems to be a filler arc on the way from Zou to Whole Cake Island which explicitly mentions Nami plotting the route using a map (Episode 775). Not included in the main answer since this isn't 100% canon, but it's certainly believable (though one could argue that Nami was in possession of Big Mom's vivre card).

In case you are wondering how no one just came across Laugh Tale (given enough time) if people can simply traverse the sea using maps, I would speculate this is due to 2 reasons:

1. It is in an unmapped area that has very low traffic
2. It is hidden by some means that can only be countered with information from the Road Poneglyphs

It shouldn't be very hard for someone like Kizaru to just go across the entire sea grid by grid since his Pika Pika No Mi allows him to travel at "the speed of light". Others like Aokiji (who can freeze the water surface) or Brook (who runs on top of water) might take an impossibly long time, but that isn't a concern for Kizaru. Thus, it is likely the island is hidden somehow beyond an unknown location.