CODEWITHSUNDEEP
javamathfloating-pointgpslatitude-longitude
RainbowQoP
RainbowQoP

Reputation: 3

How to precisely calculate distances in Java?

I'm using an implementation of this answer to calculate the distance between two points for my GPS tracking software.

However I've read on numerous StackOverFlow that using double is bad because of the inaccurate float representation of values. Therefore, I'm asking :

Upvotes: 0

Views: 267

Answers (2)

Joni
Joni

Reputation: 111219

No, using BigDecimal instead of double will not significantly improve the accuracy of this algorithm.

The main source of error is a modeling error: you're using a formula that assumes the Earth is a perfect sphere. This means the result can be wrong by as much as 0.5%. The rounding error you get from using double is on the order of 0.000000000001%.

To get more accurate results, you could use for example Vincenty's formulae, which assumes the Earth is an ellipsoid, but it is harder to implement than the great circle distance. To get even more accurate results, you should take into account the local topography, which is even harder.

For further reading: https://en.m.wikipedia.org/wiki/Geographical_distance

Upvotes: 3

Joachim Sauer
Joachim Sauer

Reputation: 308001

Yes, in theory doing any calculations in BigDecimal could lead to better precisions, but that is very unlikely to actually help for several reasons:

  • as you found out there are non-naive algorithms to calculate the distance using only double without an excessive numerical error.
  • the precision of double values for this use case is many orders of magnitude higher than the precision and accuracy of any positional information you might start out with. That means that the measurement error will definitely be bigger than the numerical error caused by using double.

And if you did your calculations in BigDecimal anyway and then converted the result to double, then you'd lose precision, of course, since BigDecimal can be effectively arbitrarily precise, but double can't.

But again: that loss of precision is irrelevant for the use case you describe.

Upvotes: 1

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