Without modern electronics, how could you determine your longitude, latitude, and altitude while lost deep underground?

Brief setting notes: it's a "basically earth" type situation, a spinning ball of rock in space with the same size and gravity and atmosphere and magnetic fields and everything else.

The main difference is that there is also a HUGE dungeon-cave system across the continent. No one knows how deep it goes, or how extensive it is. People have been exploring it for hundreds of years, using it for travel and trade, towns have been built around the entrances, and decent amounts of society and industry are built around it. But because of how large it is, and how inherently difficult it is to navigate in caves, only tiny fractions of it have been mapped, and what lies in the deepest depths is largely unknown.

Things are about at a 1890s level of technology, and many people are all trying to solve the problem of underground navigation. When you're travelling underground for weeks and months at a time, knowing where you are can get almost impossible. Compasses help, but they only do so much, and there's no sun or stars to help determine latitude, to say nothing of longitude or altitude (which is often what people really want to know, no use in bragging about how you've been deeper than any other explorer if you don't know how deep you actually are.)

So, given the technology that would realistically exist at about this time, is there some sort of surveying method or mechanism, portable and handy enough to be carried with the average explorer, which lets them know exactly where they are in terms of longitude, latitude, and altitude?

posted over 4 years ago

possiblySerious‭

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